Fossil Primates

Ignacio Arenillas & José Antonio Arz. 21st Century Anthropology: A Reference Handbook. Editor: H James Birx. Volume 2. Thousand Oaks, CA: Sage Reference, 2010.

Primates are mammals included in the order Primates, which was defined by Carolus Linneaus in 1758 in order to group lemurs, monkeys, apes, and humans. Except for humans, most Primates live in the tropical or subtropical regions of Africa, Asia, and the Americas. The Primates have been traditionally subdivided into two main informal groups: prosimians and simians. Members of the first group have traits most like those of the earliest Primates; they include tarsiers, lemurs, galagos, lorises, and aye-ayes (among others). The second group includes the New World and Old World monkeys in addition to the apes and humans.

Primates have a general morphology but exhibit a wide range of characteristics. Many species are sexually dimorphic, with females and males differing in size, certain physical traits, and coloration. This dimorphism is mainly exhibited in simians and humans. Primates are characterized by their large brains (particularly in anthropoids) and stereoscopic vision, and most have opposable thumbs. Most of them live in trees, possessing adaptations for climbing. They have various locomotion techniques, such as leaping from tree to tree, walking on four or two limbs, knuckle-walking, and brachiation (swinging between branches of trees).

The order Primates is included in the superorder Euarchontoglires, infraclass Eutheria, class Mammalia, phylum Chordata, and kingdom Animalia. In addition to Primates, the superorder Euarchontoglires (also called Superprimates) includes rodents, rabbits, tree shrews, and colugos. This superorder is divided into two clades: glires and euarchonta, the last of which includes two other sister clades, scadentia (tree shrews or tupaiis) and primatomorpha. This last clade includes three orders, two of them extant: Dermoptera (flying lemurs) and Primates and one fossil, Plesiadapiformes.

Although they do not possess a common diagnostic character, Primates can be grouped together because all of them have a common origin. They show some distinctive progressive evolutionary trends, such as toward the enlargement of the brain, predominance of the visual sense, and improved manipulative capacities. The most primitive Primates may have existed more than 65 million years ago, in the late Cretaceous, and even 85 million years ago according to some DNA molecular-clock studies. The Cretaceous ancestors of Primates were small and generalists in diet and behavior. This allowed them to survive the Cretaceous/Tertiary mass extinction, which ended the dinosaur era. Our ancestors survived by being small, omnivorous, and flexible in their behavior within diversified environments.

The late Paleocene Plesiadapis is suggested as the oldest known fossil Primate (55-58 million years ago), although most paleoprimatologists consider it belonging to a different order (order Plesiadapiformes) closely related not only to the Primates but also to the flying lemurs (order Dermoptera) and perhaps to the bats (order Chiroptera). They are characterized by long tails, agile limbs, rodentlike jaws and teeth, eyes at the side of the head, and no postorbital bar. The order Plesiadapiformes diverged during the Paleocene into several families such as Plesiadapidae, Carpolestidae, Saxonellidae, Microsyopidae, Paromomyidae, and Picrodontidae. Purgatorius, a 65-million-year-old fossil primatomorph, might be the precursor to the Plesiadapiformes and all Primates. They have primatelike characteristics, such as enlarged central incisors and molarlike terminal premolars.

Primates are subdivided into two great suborders: Strepsirrhini and Haplorrhini. Both sister clades, strepsirrhines and haplorrhines, parted ways about 63 million years ago, according to molecular-clock analyses. The first representatives of both groups were prosimians, which have adaptations to preying on small, quick-moving prey in an arboreal setting (visual predation): grasping hands and feet, nails instead of claws, eyes rotated forward (enhancing stereoscopic vision), and the elaboration of visual-sensory pathways. Both strepsirrhines and haplorrhines evolved from the ancestral Primates’ lineage (Plesiadapiformes), which included the most primitive strepsirrhines and the extinct Adapiformes as well as the most primitive haplorrhines and the extinct omomyids. These early Primates split off during the Eocene, an epoch characterized by climatic warming. The Primates’ rain forest habitat was very widespread during the Primates’ acme of the Eocene.

Strepsirrhines

The suborder Strepsirrhini includes the “wet-nosed” Primates (lemurs, lorises, galagos, aye-ayes, indris, etc.), which are considered the most primitive in features and adaptations. Their brain capacity tends to be smaller than that of the haplorrhines, indicating a lower intelligence. Their nose is connected to the upper lip, which is connected to the gum. Their nickname “wet-nosed” comes from the presence of a rhinarium, that is, the wet, naked surface around the nostrils of the nose typical of many mammals. Almost all strepsirrhines have a toothcomb, that is, tightly clustered incisors and canine teeth.

Strepsirrhines are composed of four infraorders: Adapiformes, Chiromyiformes, Lorisiformes, and Lemuriformes. The first group is a fossil taxon typically called adapids; the second includes the enigmatic, extant aye-ayes; the third group is typically called lemurs; and finally, the fourth group includes lorises, indris, and galagos. Strepsirrhines also include some incertae saedis fossil taxa, such as Azibius (middle Eocene), Panobius (middle Eocene), Lushius (late Eocene), and Shizarodon (early Oligocene).

Adapiformes

Infraorder Adapiformes, also called adapids, primarily radiated during the Eocene between 55 and 34 million years ago, although an endemic Asian group, the sivaladapids, survived into the Miocene. Adapid fossils are found in all Holarctic continents (Africa, Eurasia, and North America), together with the great fossil group of Eocene Primates, the omomyids. Adapids have small eye orbits and elongate skulls and were adapted to folivorous or frugivorous diets, which is indicated by their cheek teeth.

Adapiformes are subdivided into five families: Caenopithecidae, Nothactidae, Sivaladapidae, Omanodonidae, and Adapidae. They also include a group of incertae saedis genera, such as Simonsia, Alsatia, and Kohatius of the late Eocene; Hallelemur and Chasselasia of the middle Eocene; and Petrolemur of the late Paleocene to middle Eocene. The family Caenopithecidae includes four genera: early middle Eocene Aframonius, middle Eocene Caenopithecus, and late Eocene Mahgarita as well as middle Eocene Adapoides, whose fossils come from Africa, Eurasia, and North America. They lacked some of the typical specialization of the Adapiformes (in the dentition) but have affinities with the cercamoniine and nothactids.

The family Nothactidae is an extensive group of adapiforms, which is subdivided into three subfamilies, each one with several genera: early Eocene-early Oligocene subfamily Cercamoniinae (including the genera Anchomomys, Buxella, Barnesia, Donrussellia, Europolemur, Agerinia, Pronycticebus, Cercamonius, Protoadapis, Periconodon, andWadilemur), early middle Eocene subfamily Nothactinae (including the genera Cantius, Notharctus, Pelycodus, Copelemur, Smilodectes, and Hesperolemur), and middle late Eocene subfamily Pondaunginae (including the genera Siamopithecus, Amphipithecus, Bugtipithecus, and Pondaungia). They possessed a generally long muzzle, opposable thumbs, big toes, flexible limbs, a long tail, and a supple back. The most famous nothactid is the middle Eocene Notharctus, which had extremely long digits and skeletal proportions that resemble the living lemurs (about 7 kg in weight). Older and smaller (1-3 kg in weight) was the early middle Eocene genus Cantius, a diurnal, arboreal, and quadrupedal prosimian. The primitive cercamoniine Donrussellia might be close to a common ancestor of the adapids.

The family Adapidae includes species that are characterized by forward-facing eyes, a postorbital bar, a large brain, a reduced snout, and vertical incisors. It has been subdivided into two subfamilies: the early late Eocene subfamily Pronycticebinae (including the genera Pronycticebus and Agerinia) and the early Eocene-early Oligocene subfamily Adapinae (including the genera Microadapis, Leptadapis, Adapis, Palaeolemur, Cryptadapis, and Godinotia). The most characteristic member was the late Eocene genus Adapis, a prosimian that was diurnal, folivorous, and a slow arboreal quadruped similar to the slow lorises. Their dental formula was 2/2 (incisors), 1/1 (canines), 4/4 (premolars), 3/3 (molars) = 40 teeth.

Adapiform evolutionary relationships are controversial, but it is widely accepted (according to the postcranial skeleton characteristics) that they belong to the strepsirrhines. However, the most primitive adapiforms lacked many of the anatomical specializations of present strepsirrhines (e.g., lack of a toothcomb), suggesting that they are the basal group of strepsirrhines.

During the late Eocene and mainly during the Eocene-Oligocene transition, the climate changed, becoming very cool. It was a large extinction episode in which many large mammals disappeared, including almost all the adapiforms. The mid- to high-latitude vegetation changed dramatically from broadleaf evergreen rain forest to deciduous forest. Remnant Primates were forced to cluster into smaller forest areas near the equator. Among the survivors, there was a reduced group of adapiforms belonging to the families Omanodonidae and Sivaladapidae. The family Omanodonidae includes only one known genus, the early Oligocene Omanodon, which was related to primitive anthropoids. The family Sivaladapidae includes late Miocene adapiforms of 2 to 5 kg in weight and adapted to a folivorous diet. It has been subdivided into two subfamilies: the middle late Eocene subfamily Hoanghoniinae (including the genera Hoanghonius, Guangxilemur, Rencunius, and Wailekia) and the middle late Miocene subfamily Sivaladapinae (including the genera Sivaladapis, Indraloris, and Sinoadapis).

Lorisiformes

The infraorder Lorisiformes includes African and Asian strepsirrhines typically known as galagos or lorises. They are closely related to both the Chiromyiformes (aye-ayes) and the Lemuriformes (lemurs), but it is currently unknown whether the Chiromyiformes (aye-ayes) represent a form ancestral to both the Lemuriformes and Lorisiformes or are simply related more closely to the Lemuriformes. DNA molecular-clock analyses suggest that chiromyiforms and lemuriforms constitute a clade that diverged from the Lorisiformes about 50 million years ago. The infraorder Lorisiformes included three families, two of them extant: Lorisidae and Galagidae and the fossil family Plesiopithecidae.

The family Plesiopithecidae includes only one known fossil genus: Plesiopithecus (late Eocene species P. teras). The 36-million-year-old genus Plesiopithecus is clearly a strepsirrhine prosimian, although mandibular and molar morphologies resemble those of the archaic members of the anthropoids. Its dental formula was 2/0 (incisors), 1/1 (canines), 4/4 (premolars), 3/3 (molars) = 34 teeth, the canines being very large. It was a frugivorous, lorislike prosimian, probably without close ties to extant strepsirrhines. Molecular-clock analyses suggest that lorisids and galagids diverged about 23 million years ago, so the plesiopithecids may be the last common ancestor of both extant families.

The family Lorisidae includes the modern lorids, such as lorises, pottos, and angwantibos, which live in tropical central Africa and south Asia. They are arboreal, diurnal, and predominantly insectivorous, but they can also consume bird eggs, small vertebrates, fruits, and sap. Their size is short, between 17 and 40 cm in length, and 0.3 to 2 kg in weight. Their face is forward and their eyes are large. Their dental formula is 2/2 (incisors), 1/1 (canines), 3/3 (premolars), 3/3 (molars) = 36 teeth. Their thumbs are opposable, but their index fingers are short. They are subdivided into two great subfamilies: Lorisinae, which includes the extant genera Arctocebus (angwantibos) and Loris (slender loris), and Nycticebinae or Perodicticinae, which includes the extant genera Perodicticus (pottos), Pseudopotto (false pottos), and Nycticebus (slow loris). The first subfamily, Lorisinae, includes besides two other fossil genera, Mioeuoticus (early Miocene) and Karanisia (late Eocene); the second subfamily includes Nycticebinae and the other fossil genus Nycticeboides (late Miocene).

The family Galagidae includes the small, nocturnal lorisiforms known as galagos. They are agile leapers and run swiftly along branches and are omnivorous but mainly insectivorous. They have large eyes, strong hindlimbs, and long tails. Like lorids, their dental formula is 2/2 (incisors), 1/1 (canines), 3/3 (premolars), 3/3 (molars) = 36 teeth. Galagids include four extant genera, Otolemur (greater galagos), Euoticus (needle-clawed bush babies), Galago, and Galagoides (lesser galagos), as well as the three fossil genera Saharagalago (late Eocene), Progalago (early Miocene), and Komba(early middle Miocene).

Chiromyiformes

The infraorder Chiromyiformes includes only one extant species (Daubentonia madagascariensis), which is included in the family Daubentoniidae. They are the aye-ayes, dwellers of rain forests or deciduous forests. They do not exhibit sexual dimorphism, being of 30 to 40 cm in body length and 45 to 55 cm tail lengths. Their face and teeth are rodentlike and their body squirrel-like. The teeth number of Chiromyiformes is very reduced, their dental formula being 1/1 (incisors), 0/0 (canines), 1/0 (premolars), 3/3 (molars) = 9 teeth. They possess opposable thumbs much like other Primates, although both the hallux and fingers are long and slender.

This is an enigmatic group whose phylogenetic relationships are not clear. No fossils of Chiromyiformes have been found. The only other known species, Daubentonia robusta (giant aye-aye), became extinct at the beginning of the 20th century. If they represent a basal group to all the strepsirrhines, then they might have evolved 63 million years ago; but if they are simply a sister clade to Lemuriformes, then they might have evolved 50 million years ago. Molecular-clock analyses suggest that Chiromyiformes and Lemuriformes diverged more than 45 million years ago.

Lemuriformes

The infraorder Lemuriformes includes the typically known lemurs, nicknamed as spirits of the night, or ghosts, due to their large, reflective eyes that shine at night. The infraorder is subdivided into five families: Cheirogaleidae, Megaladapidae, Lepilemuridae, Lemuridae, and Indridae. The scheme of evolutionary relationships supports the hypothesis that strepsirrhines had an African Arabian origin and that lemuriforms likely colonized Madagascar by crossing the Mozambique Channel. DNA molecular-clock analyses suggest that indrids are the more primitive among the extant lemuriforms; indrids are derived from lemurids, as were the cheirogaleids 28 million years ago.

The family Cheirogaleidae includes the dwarf and mouse lemurs, small lemuriforms living in Madagascar that are nocturnal, arboreal, and omnivorous. Their size is only 15 to 30 cm, and they weigh no more than 0.5 kg. Their dental formula is 2/2 (incisors), 1/1 (canines), 3/3 (premolars), 3/3 (molars) = 36 teeth. They comprise five extant genera, Cheirogaleus, Microcebus, Mirza, Allocebus, and Phaner, and one known fossil genus, Bugtilelemur (the late Oligocene species B. mathesoni). Although they include the earliest known fossils of lemuri-forms, DNA molecular-clock analyses suggest that they are a more derived group.

The family Megaladapidae is extinct and includes only one genus: Megaladapis (Pleistocene-Holocene species M. brachycephalus, M. dubius, M. edwarsi, M. grandidieri, M. insignis, and M. madagascariensis). Its species lived in Magadascar and became extinct only 500 years ago. They were large, between 1.3 and 1.5 m in length, and had long arms and fingers (specialized for grasping trees) and legs adapted for vertical climbing. They are closely related to the lepilemurs, which were for a time included with the megaladapids. The family Lepilemuridae includes the sportive lemurs (Lepilemur), a medium-sized lemuri-form with a 30 to 35 cm length and 0.9 kg weight. They are herbivorous, strictly nocturnal, and predominantly arboreal. No fossil species belonging to this family has been found, and sportive lemurs are known only during the recent Holocene.

The Pliocene-Recent family Lemuridae includes the typical lemurs. They are medium-sized lemuriforms, arboreal, quadrupedal, agile, and herbivorous. They are 30 to 55 cm in length and 0.7 to 5 kg in weight. Their hindlimbs are slightly longer than their forelimbs. Their dental formula is 2/2 (incisors), 1/1 (canines), 3/3 (premolars), 3/3 (molars) = 36 teeth. The family includes five extant genera, Hapalemur (bamboo lemurs), Prolemur (greater bamboo lemurs),Lemur (ring-tailed lemurs), Varecia (ruffed lemurs), and Eulemur (brown lemurs), and one recently extinct genus, Pachylemur (Holocene species P. insignis and P. jullyi), which lived in Magadascar and is closely related to Varecia.

The Pleistocene-Recent family Indridae includes large-sized lemuriforms known as indris. There are three extant indrid genera: Indri (indris or babakotos), Avahi (avahis or woolly indris), and Propithecus (sifakas). They are arboreal and herbivorous, and they are large in size but vary in size considerably from species to species. While the avahis are only 30 to 50 cm in length and 0.6 to 1.2 kg in weight, the sifakas are 45 to 55 cm and 4 to 6 kg and the indris are 65 to 80 cm and 8 to 13 kg. Their hind legs are longer than their forelegs, with long and thin hands. Their thumbs cannot be opposed to the other fingers correctly. Their dental formula is 2/2 (incisors), 1/1 (canines), 2/2 (premolars), 3/3 (molars) = 32 teeth. There is a fossil genus, with close ties to extant indris, called Mesopropithecus (Pleistocene- middle Holocene species M. pithecoides, M. globiceps, and M. dolichobrachion), a larger and longer-armed indrid, which became extinct only 500 years ago.

The three extant genera mentioned above and Mesopropithecus have been grouped in the subfamily Indrinae. In addition, another two extinct indrid subfamilies have been considered: Archaeolemurinae, which includes the fossil genera Hydropithecus (Pleistocene-Holocene species H. stenognathus) and Archaeolemur (Pleistocene-Holocene species A. majori and A. edwardsi); and Palaeopropithecinae, known as “sloth lemurs,” which includes the fossil generaArchaeoindris (early Holocene species A. fontoynonti), Babakotia (Holocene species B. radofilai), and Palaeopropithecus (Holocene species P. ingens and P. maximus). All of them document a wide adaptative radiation of lemuriforms in Madagascar from their arrival on the island to little more than 1,000 years ago. Hydropithecus was a large lemuriform up to 13 kg in weight, probably terrestrial, that lived until recently (less than 1,000 years ago), becoming extinct probably before the arrival of humans to the island of Madagascar. Archaeolemur was semiterrestrial, about 17 kg in weight, and clearly related to the living indrids. Both archaeolemurine genera belonged to the ancestral group of the indrids. Palaeopropithecus was a large-sized, climber-hanger lemuriform, with a dental formula of 2/2 (incisors), 1/0 (canines), 2/2 (premolars), 3/3 (molars) = 30 teeth, that is, with a canine lacking on the lower jaw.Archaeoindris was the largest of the Primates of Magadascar, which weighed almost 200 kg and measured around 1.5 m in height. Due to its weight, it should be near-exclusively terrestrial or adapted to slow, ponderous climbing, like the sloths. Babakotia was a medium-sized (approximately 15 kg in weight) indrid whose inferred positional behaviors were primarily slow climbing and hanging. The indrine genus Mesopropithecus was close to these more primitive paleopropithecines.

Haplorrhines

The suborder Haplorrhini includes the “dry-nosed” Primates, that is, prosimian tarsiers and simians, also called anthropoids. Their brain capacity is significantly greater than the strepsirrhines’ brain capacity. Haplorrhines include two great groups or clades sometimes considered as suborders: Tarsiiformes and Anthropoidea. In the latter case, both haplorrhines and strepsirrhines should rise to an upper category, perhaps as semiorders. DNA molecular-clock analyses indicate that tarsiiforms and anthropoids parted ways 58 million years ago.

Tarsiiformes

The Tarsiiformes include the modern tarsiers (genus Tarsius), living on the islands of southeastern Asia. They are the most primitive group of the haplorrhines. They were widespread in the past, their fossils being found in Eurasia and North America and perhaps in Africa. This group is often classified as an infraorder although others consider that this group should be elevated to an upper category (suborder Tarsiiformes). Tarsiiformes represent a link between toothcombed strepsirrhines and the anthropoids. They include only one infraorder: Tarsioidea.

The carpolestid is an extinct family traditionally included in Plesiadapiformes, but it has been considered on some occasions as belonging to Tarsiiformes. Carpolestids are relatively late Paleocene-early Eocene Tarsiiformes-like Plesiadapiformes of Eurasia and North America. Their size was similar to that of a mouse, approximately 0.02 to 0.15 kg in weight. They were characterized by two large upper-posterior premolars and one large lower-posterior premolar. Carpolestids have been considered the ancestor of both tarsioids and anthropoids and classified as a second infraorder (Carpolestoidea) within the clade tarsiiforms. Nevertheless, the phylogenetic relationships of these groups are not clear. Among the known genera are the Carpodaptes of the early Paleocene to early Eocene (62-50 million years ago), Elphidotarsius of the early to the late Paleocene (62-56 million years ago), Carpolester of the middle to late Paleocene (60-56 million years ago), and Chronolestes of the early Eocene (55-49 million years ago).

The infraorder Tarsioidea includes the modern tarsiers or prosimian haplorrhines, which are grouped in the family Tarsiidae. It also comprises fossil species of two other extinct families: Omomyidae and Afrotarsiidae. The family Omomyidae is the most primitive and includes the typically known omomyids, all extinct, that radiated during the Eocene between 55 and 34 million years ago. Their fossils have been found in North America, Eurasia, and possibly Africa and are the most remarkable Primates of the Eocene together with the strepsirrhine adapids. Their size was relatively small, with a weight less than 0.5 kg, although some reached more than 1 kg. They had a large brain, large eye orbits, a narrow gap between the eyes, and a short face with dental arcades. Their dental formula was 2/2 (incisors), 1/1 (canines), 2/2 or 3/3 (premolars), 3/3 (molars) = 32 to 34 teeth. They were frugivorous or folivorous and presumably still had a rhinarium, that is, a wet nose, indicating that they were a very primitive haplorrhine. Many paleoprimatologists consider them a basal member of all haplorrhines, that is, the base of both tarsiiforms and anthropoids. However, others consider them a basal member of only the tarsiiforms, whereas still others consider them related to adapids and carpolestids.

Omomyids have been subdivided into three subfamilies, Anaptomorphinae, Microchoerinaea, and Omomyinae, and a group of incertae saedis genera, probably primitive members of the family Omomyidae. Among these last are includedAltiatlasius of the late Paleocene (58-56 million years ago) and Altanius of the early Eocene (58-56 million years ago). The age of these fossil genera is consistent with the DNA molecular-clock analyses, whether or not they are considered the ancestor of both tarsiiforms and anthropoids. The subfamily Anaptomorphinae includes an extensive group of primitive omomyids, which include Trogolemur of the middle and late Eocene (48-40 million years ago), and both Teilhardina and Tetonius of the early Eocene (58-56 million years ago). Teihardina, an insectivorous tarsier-like omomyid of 0.1 kg in weight, may also be near the base of the radiation that produced all living haplorrhines. Among the genera of the subfamily Microchoerinaea are included Pseudoloris of the middle Eocene to early Oligocene and Necrolemur of the middle to late Eocene. The most extensive group of omomyids is the subfamily Omomyinae, which includes well-known genera such as Omomys and Shoshonius of the early Eocene, Utahia of the early to middle Eocene, Macrotarsius of the middle Eocene to early Oligocene, and Rooneyia of the late Eocene to early Oligocene. The approximately 50-million-year-old genus Shoshonius was a 0.15-kg-in-weight prosimian with a very similar morphology to the modern tarsier. The 50- to 45-million-year-old genus Omomys was more similar to galagos than to tarsiers in its morphology, being 0.3 kg in weight.

The family Tarsiidae includes small prosimians with enormous eyes, very long hindlimbs, and extremely elongated feet. Unlike other prosimians, tarsiers have no tooth-comb for which they were definitively classified within haplorrhines and not within the strepsirrhines like the rest of the prosimians. Their dental formula is 1/1 (incisors), 1/1 (canines), 3/3 (premolars), 3/3 (molars) = 32 teeth. They are primarily insectivorous, although they also eat small vertebrates. The family Tarsiidae includes eight species, including Tarsius syrichta (Philippine tarsier), Tarsius bancanus (Horsfield’s tarsier), Tarsius tarsier (spectral tarsier), and Tarsius pumilus (pygmy tarsier). T. bancanus is a fossil species from the middle Eocene about 45 million years ago. Other extinct fossil species have been found, such as Tarsius eocaenus of the middle Eocene (about 45 million years ago) and Tarsius thailandica of the early Miocene (about 20 million years ago). The other extinct family of the infraorder Tarsioidea, the family Afrotarsiidae, is closely related to extant tarsiers. It is a fossil group of particular interest in questions about the origin of tarsier specializations and the early tarsioid radiations during the early and middle Oligocene (33-26 million years ago). Only one genus, Afrotarsius, and only one species, Afrotarsius chatrathi, of this family are known to date.

Anthropoids

The anthropoids, also called simiiforms, include the simians, that is, the higher Primates, such as the familiarly known monkeys, apes, and humans. Like Tarsiiformes, this group is often classified as an infraorder, the infraorder Anthropoidea, although others consider that it should be elevated to an upper category (suborder Anthropoidea). This taxon is traditionally subdivided into two great infrarorders, Platyrrhini and Catarrhini, but there are some primitive fossil anthropoids whose assignment to one of these two infraorders is debatable.

The most primitive anthropoids belong to the group called informally palaeoanthropoid, which could be considered a new infraorder (“Palaeoanthropoidae”). It includes two families: “Palaeoanthropidae” and Pondaungidae. The first family includes genera such as Myanmarpithecus (middle Eocene species M. yarshensis) and Djebelemur (early Eocene species D. martinezi). The second family has been subdivided into two subfamilies: Siamopithicini, which includes the genus Siamopithecus (late Eocene species S. eocaenus), a primitive, medium-sized (7 kg in weight) palaeoanthropoid; and Pondaungini, which includes the genera Amphipithecus (late Eocene species A. mogaungensis) and Pondaungia (middle late Eocene species P. cotteri and P. savagei) as well as other palaeoanthropoids of medium size (7 kg in weight) and frugivorous.

Platyrrhines and catarrhines split from the ancestral simian line about 50 million years ago (late Eocene), the first ones occupying the New World and the second ones occupying the Old World. DNA molecular-clock analyses suggest that platyrrhines and catarrhines diverged about 40 to 45 million years ago. Earlier fossil members of anthropoids of both platyrrhines and catarrhines had small brain sizes, but the larger brain sizes seen in both groups today must have arisen independently. This documents that large brains evolved separately several times within the Primates.

Platyrrhines

The infraorder Platyrrhini includes the New World monkeys of Central and South America, such as the titis, tamarins, marmosets, capuchins, and so on. They are small or medium-sized anthropoids, which differ from catarrhines mainly by a flat nose and by having 12 premolars instead of 8. Their dental formula is 2/2 (incisors), 1/1 (canines), 3/3 (premolars), 3/3 (molars) = 40 teeth. Almost all platyrrhines are arboreal and show substantial paternal care of the young.

About 50 million years ago, the ancestral anthropoids split into platyrrhines and catarrhines. The first platyrrhines surely migrated across the Atlantic Ocean from Africa to South America, perhaps on a raft of vegetation similar to the vast pieces of floating mangrove forest that storms occasionally break off at present from the tropical African coast. The infraorder Platyrrhini is subdivided into six families: Branisellidae, Callitrichidae, Atelidae, Pitheciidae, Cebidae, and Aotidae (the first of which is one fossil group of primitive platyrrhines). DNA molecular-clock studies indicate that cebids, aotids, and callitrichids constitute a clade, diverging one from another 20 million years ago; cebids are the most primitive group of this clade and callitrichids the most derived. In addition, atelids and pitheciids form other clades. Both clades diverged 25 million years ago.

The extinct family Branisellidae is composed of a single genus, Branisella (late Oligocene species B. boliviana). This genus lived 26 million years ago in South America, and it is an interesting fossil because of its dental similarity with the Oligocene Proteopithecus, a primitive catarrhine. This has allowed paleoprimatologists to hypothesize that the primitive platyrrhine ancestors came to South America from Africa. The modern platyrrhines, which are most closely related in morphology to Branisella, appear to be the callitrichids. Nevertheless, the first platyrrhines should be primitive monkeys close to the branisellids that shared traits common to all the first representatives of each platyrrhine family.

The family Cebidae is an extensive group that includes the capuchin and squirrel monkeys. They are generally arboreal, diurnal, and omnivorous and mainly eat fruits and insects. Their dental formula is 2/2 (incisors), 1/1 (canines), 3/3 (premolars), 3/3 or 2/2 (molars) = 40 to 36 teeth. The family has been subdivided into two extant subfamilies (Saimiriinae and Cebinae) and three other fossil subfamilies (Palaeocebinae, Tremacebinae, and Lagonimiconinae). According to molecular-clock analyses, the two extant subfamilies, saimiriines and cebines, diverged about 20 million years ago.

The subfamily Saimiriinae includes the present Saimiri (squirrel monkeys), which live in tropical forests of Central and South America. They are small, diurnal, arboreal monkeys of 60 to 75 cm (of which 35-40 cm are the tail) and 0.8 to 1.1 kg in weight. They appeared in the middle Miocene, and an extinct species (S. fieldsi) is known. A fossil genus of Saimiriinae is also known, Laventiana (middle Miocene species L. annectens). Laventiana is closely related to Saimiriand Cebus, and it has been considered an intermediate taxon between squirrel monkeys (Saimiri) and callitrichids. The subfamily Cebinae includes the modern Cebus (capuchin monkeys or capuchins), which appeared in the Pleistocene, and a fossil genus Dolichocebus (late Oligocene species D. gaimanensis). Capuchins are small monkeys of about 30 to 45 cm in body length and 4 kg in weight. They are characterized by a prehensile tail and a small brain capacity (about 80 cm3).Dolichocebus lived 25 to 24 million years ago, and it is strongly related to the Saimiriinae lineage.

The extinct subfamily Palaeocebinae includes three genera: Chilecebus (early Miocene species C. carrascoensis), Patasola (middle Miocene species P. magdalenae), and Antillothrix (late Pleistocene-middle Holocene species A. bernensis). The 20-million-year-old genus Chilecebus was a small monkey of about 0.6 kg, with a smaller relative brain size than the brain of modern Cebidae. Patasola shares dental features with callichitrids and saimirines, suggesting that they are the first descendants of the cebids. Antillothrix has close ties to cebid capuchins and is nicknamed the Hispaniola monkey since it was found on the island of Hispaniola.

The extinct subfamily Tremacebinae includes only one genus, Tremacebus (late Oligocene-early Miocene species T. harringtoni), a Patagonian monkey of about 1 m in length closely related to modern night monkeys (Aotus). The extinct subfamily Lagonimiconinae includes a single genus, Lagonimico (middle Miocene species L. conclutatus), a giant tamarin-like cebid of about 1.2 kg that lived 13.5 million years ago.

The family Aotidae includes the modern Aotus (from the middle Miocene). They are the night monkeys, also called owl monkeys or douroucoulis, living in the forests of Central and South America. They are nocturnal, arboreal, quadrupedal, and omnivorous monkeys, including insects and small vertebrates in their diet. They are small to medium-sized monkeys of 50 to 100 cm in length (including a 20-50 cm tail) and 0.5 to 1.3 kg in weight. One fossil species of the middle Miocene is known, the 12-million-year-old Aotus didensis. It could be related to primitive atelid Xenothrix.

The family Callitrichidae includes some types of marmosets and tamarins, which are the smallest of the anthropoids. All of them are arboreal and mainly insectivorous and frugivorous, although some also eat small vertebrates. The family consists of two subfamilies: Callimiconinae and Callitrichinae, which diverged 13 million years ago according to molecular-clock studies. The first one includes the modern genus Callimico (species C. goeldii or Goldei’s marmoset) and the fossil genus Mohanamico (middle Miocene species M. herskovitzi). Callimico is a small Amazonian marmoset of 50 cm in length (30 cm of which are the tail). The second family includes three extant genera, Leontopithecus, Saguinus, and Callithrix, and one fossil genus, Micodon (middle Miocene species M. kiotensis). Callithrix includes the marmosets and is sometimes divided into four species: Callithrix (Atlantic marmosets), Mico (Amazonian marmosets), Callibella (Roosmalen’s dwarf marmosets), and Cebuella (pygmy marmosets). They are very small monkeys, most of which are about 15 to 25 cm in body size and about 0.4 kg in weight. Saguinus includes the tamarins, small omnivorous monkeys of 50 to 70 cm in length (30-40 cm of which are the tail) and about 0.3 to 0.9 kg in weight. Leontopithecus are the lion tamarins, small, diurnal, tree-dweller monkeys of 75 cm in length (45 cm of which are the tail) and about 0.9 kg in weight. No fossil species are known of these genera although the living species have fossils known from the Pleistocene. The middle Miocene genus Mohanamico was a small extinct marmoset of about 1 kg in weight that lived in Amazonia.

The family Pitheciidae includes the titis, saki monkeys, and uakaris. They are small or medium-sized monkeys, diurnal, arboreal, quadrupedal, and predominantly herbivorous (fruits and seeds), although some also eat insects. The family consists of two subfamilies: Pitheciinae and Callicebinae (or Homunculinae). DNA molecular-clock analyses indicate pitheciines and callicebines parted ways 17 million years ago.

The subfamily Pitheciinae consists of three extant genera, Pithecia, Chiropotes, and Cacajao, all of which are known only from the Holocene. Pithecia includes the sakis or saki monkeys, which reach 60 to 100 cm in length (of which 30-50 cm are the tail) and about 1.8 to 2.2 kg in weight and are omnivorous (including small rodents and bats in their diet). They have close ties to Chiropotes, the bearded sakis, medium-sized monkeys of similar length but more weighty (2-4 kg) than Pithecia. Cacajao includes the uakaris, which have tails (15-18 cm) of substantially less length than their bodies (40-45 cm). According to the DNA molecular-clock analyses, the Chiropotes-Cacajao group diverged from the Pitheciagroup about 10 million years ago. In addition, five extinct genera have been recognized within the pitheciines: Soriacebus (early Miocene species S. ameghinorum and S. adriane), Proteropithecia (middle Miocene species P. neuquenensis), Cebupithecia (middle Miocene species C. sermientoi), Nuciraptor (middle Miocene species N. rubricae), and Mohanamico (middle Miocene species M. hershkovitzi). Some of the dental and mandibular characteristics of Soriacebus resemble the callichitrids, while those of Proteropithecia suggest a relationship with callicebines. Mohanamico is a problematic genus that has been related to the callichitrids but also to Aotus.

The subfamily Callicebinae consisted of one modern genus: Callicebus (from the Pleistocene), which is sometimes subdivided into two genera (Callicebus and Torquatus). They are the titis or titi monkeys, small monkeys that have a furry tail (25-55 cm) longer than the body (25-45 cm). The subfamily Callicebinae also includes two extinct genera: Homunculus (early middle Miocene species H. patagonicus) and Carlocebus (early Miocene species C. carmenensis andC. intermedius). The first genus was a diurnal, omnivorous monkey, which seems to be related to both the cebid Tremacebus and the atelid Brachyletes. Carlocebus was another callicebine, predominantly frugivorous, closely related to the modern Callicebus.

The family Atelidae includes the only Primates whose tails are prehensile (in addition to capuchins). They are the howler, spider, and woolly monkeys, which live in the dense rain forests of Central and South America. Atelids are small to medium-sized monkeys, arboreal, diurnal, quadrupedal, and predominantly frugivorous and folivorous, although some species also eat insects. The family Atelidae is subdivided into three subfamilies, one extinct, Xenotrichinae, and two extant, Alouattinae and Atelinae. The subfamily Xenotrichinae recently became extinct, with only one genus and species known: genus Xenothrix (Pleistocene-Holocene species X. mcgregori). Members of Xenothrix are nicknamed the Jamaican monkeys, which share a close affinity with both pithecids and aotids. According to DNA molecular-clock analyses, the two extant subfamilies, alouattines and atelines, diverged about 16 million years ago.

The subfamily Alouattinae includes the modern Alouatta (from the Pleistocene), familiarly called howler monkeys. They have prehensile tails, move quadrupedally (but do not brachiate), and are only folivorous. Alouattines also include three extinct fossils: Protopithecus (late Pleistocene-early Holocene species P. brasiliensis), Paralouatta (early Miocene-late Holocene species P. veronai and P. marinae), and Stirtonia (middle late Miocene species S. tatacoensis and S. victoriae). Protopithecus was a large monkey (25 kg in weight), with characteristics resembling the two atelid subfamilies. Paralouatta seems to be intermediate between the xenotrichines and modern alouattines. Stirtonia could be near the ancestry of the atelines.

The subfamily Atelinae includes the modern Ateles (spider monkeys) and the group formed by the genera Brachyteles(muriquis), Lagothrix (woolly monkeys), and Oreonax (yellow-tailed woolly monkeys). In addition, one extinct genus is known, Caipora (late Pleistocene-early Holocene species C. bambuiorum). The living species are diurnal, arboreal, and omnivorous monkeys, characterized by prehensile tails capable of supporting their entire body weight. Spider monkeys (Ateles) are known from the Pleistocene and are medium-sized monkeys about 90 cm in length (including a 40-cm tail) and 6.5 kg in weight. Muriquis (Brachyteles), also known as woolly spider monkeys, are mainly folivorous monkeys of 40 to 60 cm in length (without their tails) and 4.5 to 9 kg in weight. Woolly monkeys (Lagothrix) are also medium-sized monkeys of 100 to 140 cm in length (of which 60-80 cm are their tails) and 4 to 10 kg in weight. The fossil atelineCaipora seems to be related to the alouattine Protopithecus.

Catarrhines

The infraorder Catarrhini includes the Old World monkeys from Africa and Eurasia (colobus, mandrills, langurs, macaques, baboons, etc.) grouped in the superfamily Cercopithecoidea; the apes (gibbons, orangutans, gorillas, and chimpanzees) and humans are grouped in the super-family Hominoidea, and other fossil taxa are grouped in several superfamilies: Parapithecoidea, Propliopithecoidea, Pliopithecoidea, Dendropithecoidea, and Proconsuloidea. According to DNA molecular-clock analyses, the two living subfamilies, cercopithecoids and hominoids, parted ways about 25 million years ago. According to morphocladistic analyses, the parapithecoids are the most primitive, and from them evolved the propliopithecoids. Both superfamilies have been sometimes grouped as the paracatarrhines, whereas the four other more modern ones represent the eucatarrhines. Among the eucatarrhines, the most primitive are the pliopithecoids, from which evolved the dendropithecoids. These last ones may be the last common ancestor of the cercopithecoids and hominoids, proconsuloids being intermediate between the dendropithecoids and the hominoids.

Parapithecoids

Some paleoprimatologists have considered that the parapithecoids are the last common ancestor of both platyrrhines and catarrhines, although they are probably only the basal group of all catarrhines. The superfamily Parapithecoidea consisted of two families, Eosimiidae and Parapithecidae. The first, Eosimiidae, comprises very small primitive parapithecoids, between 0.03 and 0.3 kg in weight. They were predominantly arboreal and frugivorous. Eosimiids might be close to the ancestors of all catarrhines. Six genera are known: Bahinia (middle Eocene B. pondaungensis), Eosimias(middle Eocene species E. sinensis and E. centennicus), Biretia (late Eocene species B. piveteaui, B. fayumensis, and B. megalopsis), Phenacopithecus (middle late Eocene species P. krishtalkai and P. xueshii), Anthrasimias (early Eocene species A. gujaratensis), and Phileosimias (early Oligocene species B. kalami and B. brahuiorum). The 55- to 54-million-year-old genus Anthrasimias is probably the earliest eosimiid and has strong ties to the omomyids, such as Altiatlasius. The 40-million-year-old genus Phenacopithecus also resembles the omomyids and tarsiers, at least in its jaws, but unlike those had relatively small eyes. The 48-million-year-old genus Eosimias was a small primitive prosimian, 0.07 to 0.16 kg in weight, with catarrhine-like dental and mandibular characters. The 42-million-year-old genus Bahinia also possessed small eyes, suggesting both genera were diurnal. On the contrary, the 37-million-year-old Biretia apparently had orbits nearly as large as those of the tarsiers, evidencing nocturnality. Other traits suggest that Biretia is phylogenetically more advanced in the direction of the parapithecids. The 30-million-year-old Phileosimias is a clear eosimiid, being the latest one, but some dental characteristics still resemble the earlier omomyids and adapiforms.

The family Parapithecidae comprises small, early catarrhines that still retained three premolars. Their dental formula was 2/2 (incisors), 1/1 (canines), 3/3 (premolars), 3/3 (molars) = 36 teeth. They are therefore primitive catarrhines that retained ancestral features like the eosimiids. The family Parapithecidae has five genera known to date: Qatrania (late Eocene-middle Oligocene species Q. wingi and Q. fleaglei), Parapithecus (early middle Oligocene species P. fraasi andP. grangeri), Arsinoea (late Eocene-middle Oligocene species A. kallimos), Serapia (late Eocene-middle Oligocene species S. eocaena), and Apidium (early middle Oligocene species A. phiomense, A. moustafai, and A. bowni). The most well-known genera are Parapithecus and Apidium, the first probably near the base of the parapithecid radiation. The 36- to 32-million-year-ago genus Apidium was the smallest known of the catarrhines, approximately 30 to 40 cm in body length and 0.7 to 1.5 kg in weight. It has a short snout, small eyes, and canine sexual dimorphism. Its individuals were diurnal, quadrupedal, and frugivorous. It seems to have certain affinities to the more modern propliopithecid Aegyptopithecus. Certain dental characteristics of Apidium also resemble the oreopithecids and cercopithecoids but may well have evolved in parallel or convergently in these groups. The 36- to 32-million-year-old genera Qatrania and Arsinoea were also frugivorous but resemble Parapithecus. The 36- to 30-million-year-old genus Parapithecus was a small prosimian (1.5-3 kg in weight) and surely folivorous or a seed eater. The 36- to 32-million-year-old genus Serapia has been considered allied to the propliopithecoids, mainly to Proteopithecus, but its dental traits have allowed it to be grouped with the other parapithecids.

Propliopithecoids

The family Propliopithecoidea may be close to the common ancestry of the later catarrhines (eucatarrhines). They were primitive arboreal catarrhines the size of small cats, with apelike teeth, a small brain, and limbs similar to those of the acrobatic platyrrhine atelines. Their dental formula was already the catarrhine type: 2/2 (incisors), 1/1 (canines), 2/2 (premolars), 3/3 (molars) = 32 teeth. Propliopithecoids consisted of two important families, Oligopithecidae and Propliopithecidae.

The family Oligopithecidae is an extinct propliopithecoid family that includes late Eocene-middle Oligocene species. Its members were mainly insectivorous, according to its dental morphology. They split off the lineage of Old World monkeys and apes sometime after the New World monkeys split off. The family has three genera known to date: Proteopithecus (late Eocene-middle Oligocene species P. sylviae), Catopithecus (late Eocene-middle Oligocene species C. browni), and Oligopithecus (late Eocene-early Oligocene species O. savagei and O. rogeri). The 36- to 32-million-year-old genus Oligopithecus is the best known oligopithecid. They were small monkeys, being 1 to 2 kg in weight, that lived in Africa. Their canines resemble those of the platyrrhine and callitrichines more than those of the catarrhines, their teeth being primitive compared with other haplorrhines. As propliopithecids, they are older than Old World monkeys and apes but are already nearer the common ancestor of the extant catarrhines and cercopithecoids and hominoids. The 37- to 32-million-year-old genus Catopithecus was a 1-kg-weight arboreal, diurnal, quadrupedal oligopithecid. There is an apparently evolutionary transition from primitive Catopithecus to relatively apelike Aegyptopithecus. Similar in morphology and age to Catopithecus is Proteopithecus. Both genera have been sometimes grouped in a new family called Proteopithecidae and considered an intermediate group between propliopithecids and oligopithecids. The evolutionary transition between primitive oligopithecids and derived propliopithecids requires little more than increased body size and the concomitant shift to greater frugivory.

The family Propliopithecidae includes arboreal, quadrupedal, frugivorous catarrhines with characteristics typical of the entire superfamily Propliopithecoidea. It consists of four genera known to date: Algeripithecus (middle Eocene speciesA. minutus), Moeripithecus (Oligocene species M. markgrafi), Aegyptopithecus (late Eocene-early Oligocene species A. zeuxis), and Propliopithecus (late Eocene-middle Oligocene species P. haeckeli, P. chirobates, and P. ankeli). The most famous propliopithecid genera are these two last ones. Aegyptopithecus, nicknamed dawn ape and with a single known species (A. zeuxis), is a propliopithecid that lived 35 to 31 million years ago, predating the divergence between cercopithecoids and hominoids. It is a crucial link between both Eocene cercopithecoids and Miocene hominoids. Its body was small, being around 6 to 8 kg in weight, but with a long tail. Its cranium had a sagittal crest, and its brain capacity was very small (30 cm3 on average), although the brain contained advanced traits when compared with the strepsirrhines. Its canines showed sexual dimorphism. Its individuals were frugivorous (also folivorous), diurnal, arboreal, and quadrupedal, and they practiced suspensory behavior. Propliopithecus was a typical propliopithecid, resembling the present gibbons. They were 40 cm in length, 4 to 6 kg in weight, and diurnal, frugivorous, arboreal, and quadrupedal, with hind-climbing suspensory behavior. Algeripithecus is a single taxon because it is probably the earliest known anthropoid, living 45 million years ago. Moeripithecus is close to Propliopithecus, and some have suggested that it is a juvenile specimen of the genus.

Pliopithecoids

The superfamily Pliopithecoidea is closer to the modern catarrhines or eucatarrhines (cercopithecoids and hominoids) than to the earliest catarrhines or paracatarrhines (parapithecoids and propliopithecoids). Some pliopithecoids had shorter faces and larger brains than propliopithecoids, their brain capacity being larger (around 100 cm3). They participated in the anthropoid Primates radiation that occurred just after the middle Oligocene extinction that was caused by increased glaciation, worldwide cooling, and floral turnovers. The pliopithecoids’ and later anthropoids’ body size, like their brain capacity, was larger than that of earlier anthropoids. They became primarily frugivorous, and their sexual dimorphism suggests that the anthropoids began to live in large, complex, polygamous groups. Learning and social complexity may have served to buffer them from the extremes of the increasing variability of the Oligocene climate.

The superfamily Pliopithecoidea consisted of three families: Palaeopliopithecidae, Pliopithecidae, and Crouzeliidae. The palaeopliopithecid group includes several incertae saedis genera, such as Paidopithex (late Miocene species P. rhenatus), Kalepithecus (early middle Miocene species K. songhorensis), Limnopithecus (early middle Miocene L. legetet and L. evansi), and Kamoyapithecus (late Oligocene K. hamiltoni). The genus Kamoyapithecus is the oldest pliopithecoid, living 28 to 24 million years ago. It was a large-sized catarrhine, being 30 to 40 kg in weight. The 22- to 17-million-year-old genus Limnopithecus has some morphological similarities to Dendropithecus, suggesting phyletic relationships. It was a small African catarrhine of 4 to 5 kg in weight, arboreal, quadrupedal, and frugivorous. Kalepithecus was another small frugivorous palaeopliopithecid, being approximately 5 kg in weight and probably related to the dendropithecoids. The 10- to 9-million-year-old genus Paidopithex shared some traits with both pliopithecids and crouzelids, but its phyletic relationships are not clear.

The family Pliopithecidae is composed of the earliest apes that combined primitive features (small brain, long snout, and a tail in some species) with more advanced features (stereoscopic vision, apelike teeth, and jaws). Their dental formula generally was 2/2 (incisors), 1/1 (canines), 2/2 (premolars), 3/3 (molars) = 32 teeth. Pliopithecids are subdivided into two subfamilies, early middle Miocene Dionysopithecinae and early late Miocene Pliopithecinae. The first one has two known genera: Platodontopithecus (early middle Miocene species P. jianghuaiensis) andDionysopithecus (early middle Miocene species D. shuangouensis and D. orientalis). The 18- to 17-million-year-old genus Dionysopithecus was a small pliopithecid closely related to the dendropithecoid Micropithecus (both genera have been proposed as possible gibbon ancestors).

Another pliopithecid with similar characteristics and age was Platodontopithecus. Three genera are known of the subfamily Pliopithecinae: Egarapithecus (late Miocene species E. narcisoi), Epipliopithecus (early middle Miocene species E. vindobonensis), and Pliopithecus (middle late Miocene species P. antiquus, P. platyodon, P. zhanxiangi, andP. piveteaui.). The most well-known pliopithecid genus is Pliopithecus, which lived in Eurasia 17 to 15 million years ago. Its specimens are characterized by long arms that are well adapted to climbing trees. They seem to have links to the crouzeliid  Anapithecus. The 16- to 15-million-year-old genus Epipliopithecus had long hands and feet and long, curved fingers compared with Pliopithecus and some postcranial characteristics resembling the hominoids. These individuals were very likely agile climbers. The 9-million-year-old genus Egarapithecus had many similarities with the crouzeliids, and some paleoprimatologists include it within this family.

The family Crouzeliidae differs from its ancestors the pliopithecids mainly in dental traits. It has three known genera:Anapithecus (late Miocene species A. hernyaki), Laccopithecus (late Miocene L. robustus), Plesiopliopithecus (middle-late Miocene species P. lockeri and P. priensis), and Crouzelia (middle-late Miocene species C. auscitanensis and C. rhodanica). The 16- to 14-million-year-old genera Plesiopliopithecus and Crouzelia are today considered congeneric. They were small pliopithecoids with smaller teeth than Pliopithecus but with a similar dental formula. The 9- to 8-million-year-old genus Anapithecus was a medium-sized anthropoid, larger than all other pliopithecoids. Finally, the 8-million-year-old genus Laccopithecus was another similar crouzeliid, with canine sexual dimorphism similar to nearly all the other anthropoids. The characteristics of crouzeliids such as Anapithecus are consistent with the general conclusion that the pliopithecoids contain the last common ancestor of the cercopithecoid lineage and the dendropithecoid-proconsuloid-hominoid lineage.

Cercopithecoids

The superfamily Cercopithecoidea comprises the familiarly known Old World monkeys, such as baboons, mandrills, and macaques, which appeared between 25 and 22 million years ago. They are today native to Africa and Asia, inhabiting tropical rain forests, savannas, scrublands, and mountainous terrains. Nevertheless, they are also known in the European fossil record. Cercopithecoids are Primates of medium to large size, being the smallest of the talapoins (Miopithecus) at 35 to 40 cm in length and 0.7 to 1.3 kg in weight, and the largest of the mandrills (Mandrillus), whose males are 90 to 100 cm in length and 30 to 40 kg in weight. Unlike apes, they have a tail, for which they are also nicknamed tailed apes. Their dental formula is 2/2 (incisors), 1/1 (canines), 2/2 (premolars), 3/3 (molars) = 32 teeth, which differentiates them from apes. Most cercopithecoids are at least partially omnivorous, but they prefer a vegetarian diet. The superfamily Cercopithecoidea is composed of three families, one fossil, Victoriapithecidae, and two extant, Colobinidae and Cercopithecidae. Molecular-clock analyses suggest that the two extant families, colobinids and cercopithecids, diverged around 14 million years ago.

The family Victoriapithecidae has three known genera: Victoriapithecus (early middle Miocene species V. macinnesi), Prohylobates (early middle Miocene species P. tandyi and P. simonsi), and Adelopithecus (late Miocene species A. hypsilophus). Victoriapithecus is a single fossil, and it is the oldest cercopithecoid known to date, living 22 million years ago. It already has the typical cercopithecoid dental formula. It showed sexual dimorphism in its canines, its body mass was around 7 kg, and its mandibles were relatively deep compared with other cercopithecoids. Most famous is Prohylobates, a small to medium-sized monkey (4-25 kg) of frugivorous and folivorous diet. The victoriapithecids are the oldest cercopithecoids, all of them coming from Africa. They lived between 22 and 15 million years ago, predating the divergence of the modern families Colobinidae and Cercopithecidae. Prohylobates has been considered a possible ancestor of the colobinids, whereas Victoriapithecus could be a possible ancestor of the cercopithecids.

Unlike the cercopithecids, the colobinids are more restricted in morphology, range, and behavior pattern, and all are leaf eaters with a complicated digestive tract to facilitate the low-nutrition diet. The family Colobinidae is subdivided into three subfamilies: Palaeocolobinae, Colobinae, and Presbytinae, the two last of which have extant species. DNA molecular-clock analyses suggest that colobines and presbytines diverged 10 million years ago.

The subfamily Palaeocolobinae has two extinct genera: Dolichopithecus (late Miocene-late Pliocene species D. gallicusand D. ruscinensis) and Mesopithecus (late Miocene-late Pliocene species M. pentelicus, M. delsoni, and M. monspessulanus). This last genus, Mesopithecus, is a primitive colobinid that lived 11 to 5 million years ago, surely one of the first cercopithecoids entering Eurasia from Africa. It looks similar to the macaque, with a 40-cm length. Their individuals were semiterrestrial and adapted to both walking and climbing. They were probably anscestors of the current gray langurs (Semnopithecus). Another possible descendant is Dolichopithecus, which lived in Eurasia from about 4.5 to 2.5 million years ago. It was terrestrially adapted, even more so than any living colobine.

The subfamily Colobinae includes Old World monkeys, such as the colobines and the langurs. They are mediumsized colobinids with long tails. Most species are arboreal, but some live a more terrestrial life. They are exclusively herbivores (leaves, flowers, fruits), although they occasionally eat insects and other small animals. Colobinids are composed of three extant genera: Colobus (late Miocene-Recent), Piliocolobus (Recent), and Procolobus (Recent). Colobus are the black-and-white colobus and guerezas, which are closely related to the two other genera: Piliocolobus, the red colobus, and Procolobus, the olive colobus. They are medium- and large-sized cercopithecoids, about 125 to 150 cm in length (including a 70-80 cm tail), and between 9 and 20 kg in weight. Five extinct colobin genera are known to date:Microcolobus (late Miocene species M. tugenensis), Cercopithecoides (late Pliocene-middle Pleistocene species C. williamsi and C. kimeui), Libypithecus (late Miocene-early Pliocene species L. markgrafi), Rhinocolobus (middle late Pliocene species R. turkanensis), and Paracolobus (early Pliocene-early Pleistocene species P. chemeroni and P. mutiwa). In addition, one fossil species of Colobus has been found, C. flandrini.

The subfamily Presbytinae includes seven extant genera: Presbytis (late Miocene-Recent), or gray langurs; Semnopithecus (Pliocene-Recent), or surilis; Trachypithecus (late Pliocene-Recent), or lutungs; Pygathrix (early Pleistocene-Recent), or doucs; Rhinopithecus (early Pleistocene-Recent), or snub-nosed monkeys; Simias (Recent), or pig-tailed langurs; and Nasalis (Recent), or proboscis monkeys, also known as long-nosed monkeys. They are medium- to large-sized, diurnal, arboreal, herbivorous or frugivorous monkeys of 90 to 180 cm in length (including a 50-100 cm tail) and between 5 and 25 kg in weight. Like the colobines, they show sexual dimorphism in size. Presbytines also include one extinct genus, Parapresbytis (late Pliocene species P. eohanuman), which seems to be phylogenetically close to the palaeocolobin Dolichopithecus. Several fossil species of Presbytis (P. sivalensis), Trachypithecus (T. robustus and T. sangiranensis), and Rhinopithecus (R. lantianensis) have been also been identified.

The family Cercopithecidae includes a wide variety of forms, all of which share cheek pouches for temporary food storage and usually large incisors reflecting a frugivorous diet. It is subdivided into four subfamilies: Macacinae, Papioninae, Theropithecinae, and Cercopithecinae. Cercopithecids are represented first by the fossil papionine Parapapio, which was a semiterrestrial monkey probably close to the common ancestor of later forms, and then by several species of the highly terrestrial living Theropithecus. DNA molecular-clock analyses indicate that macacines, papionins, and theropithecines constitute a clade that diverged from cercopithecines 10 million years ago. These studies also suggest that macacines, papionins, and theropithecines parted different ways around 7 million years ago.

The subfamily Macacinae is probably the most conservative of the cercopithecids, most species retaining ancestral traits in teeth, skull, and other structures. They are closely related to Parapapio. The subfamily has one extant genus, Macaca(late Miocene-Recent), the macaques, and two fossil genera, Paradolichopithecus (late Pliocene-Pleistocene species P. arvernensis) and Procynocephalus (late Pliocene- early Pleistocene species P. wimani and P. subhimalayensis). In addition, seven fossil species of Macaca have been found: M. florentina, M. prisca, M. majori, M. libyca, M. anders-soni, M. jiangchuanensis, and M. palaeindica. The macaques are diurnal, arboreal, rain forest dwellers, omnivorous, medium-sized monkeys of 50 to 130 cm in length (including a 2-70 cm tail) and between 3 and 10 kg in weight, with sexual dimorphism in size and tail size varying considerably from species to species. They are the most widespread of the Primates, aside from humans. The fossil record of the modern Macaca indicates that they were once even more widespread than today, living in Europe in addition to North Africa and eastern Asia. A large and semiterrestrial relative, Paradolichopithecus, inhabited Europe, central Asia, and perhaps eastern Asia 4 to 1.5 million years ago. Procynocephalus was a terrestrial, large-sized macacine savanna dweller and a root, fruit, and grass eater.

The subfamily Papioninae includes species that are omnivorous, diurnal, and mostly terrestrial or semiterrestrial, although most mangabeys are arboreal and frugivorous. It has five extant genera: Papio (early Pliocene-Recent), or baboons; Mandrillus (Recent), or mandrills and drills; Lophocebus (Recent), or crested mangabeys; Rungwecebus (Recent), or kipunjis; and Cercocebus (late Pliocene- Recent), or white-eyelid mangabeys. They are medium- to large-sized monkeys of 90 to 180 cm in length (including a 50-100 cm tail) and between 8 and 60 kg in weight. They have a pronounced sexual dimorphism. No fossil species of Mandrillus, Lophocebus, Rungwecebus, or Cercocebus have been found. However, two fossil species of Papio are known, P. izodi and P. robinsoni. The subfamily Papioninae comprises, besides three extinct known genera, Parapapio (late Miocene-lower Pleistocene species P. broomi, P. joseni, P. whitei, P. antiquus, and P. ado), Dinopithecus (late Pliocene-lower Pleistocene species D. ingens), and Gorgopithecus (late Pliocene-lower Pleistocene species G. major). Parapapio was a medium- to large-sized, semi-terrestrial cercopithecid, and appears to be near the common ancestor of all papionines. Dinopithecus is one of the largest cercopithecids known, except for modern Theropithecus, is also semiterrestrial, and has a robust skull including a sagittal crest and strong nuchal crest. Gorgopithecus, nicknamed the giant baboon, was a large papionine, probably semiterrestrial, and inhabited an open environment.

The subfamily Theropithecinae is probably a recent descendant of the papionines. They are very close to Papio as suggested by molecular studies; both theropithecines and papionines diverged 4 million years ago. Theropithecinae has one extant genus: Theropithecus (early Pliocene-Recent), known as geladas, and two fossil genera, Simopithecus (Pliocene species S. darti, S. oswaldi, S. leakeyi, and S. delsoni) and Omopithecus (Pliocene-early Pleistocene species O. brumpti, O. baringensis, and O. quadrirostris). No fossil species of Theropithecus has been found, but the genus is known from 4 million years ago. Geladas are herbivorous, largely terrestrial, large-sized monkeys of 65 to 75 cm in body length, 45 to 50 cm in tail length, and between 12 and 20 kg in weight, with sexual dimorphism in size. They have the most opposable thumbs of any of the catarrhines, except for humans. The 4- to 2-million-year-old genus Simopithecus is closely related to Theropithecus, with identical terrestrial locomotor strategies, although Simopithecus possibly used arboreal substrates. The 3.5- to 1.5-million-year-old genus Omopithecus has close ties to Papio, showing the close phylogenetic relationship between papionines and theropithecines.

The subfamily Cercopithecinae is the least represented in the fossil record, except for some fossils of Cercopithecus. It is composed of four living genera: Allenopithecus (Recent), or Allen’s swamp monkeys; Cercopithecus (late Pliocene-Recent), or guenons and Mona monkeys; Chlorocebus (Recent), or vervet monkeys; Erythrocebus (Recent), or patas monkeys; and Miopithecus (Recent), or telapoins. Most are omnivorous and arboreal although Erythrocebus is among the most terrestrial of all cercopithecids, and some Cercopithecus are partially folivorous. Except for the telapoins, they are medium-sized monkeys of 90 to 140 cm in length (including a 50-75 cm tail), and between 4 and 8 kg in weight, with great sexual dimorphism. Telapoins (Miopithecus) are the smallest Old World monkeys, with typically 30 to 45 cm in body length and between 0.8 and 1.3 kg in weight.

Dendropithecoids

The extinct superfamily Dendropithecoidea is composed of one family, Dendropithecidae, with three genera: Dendropithecus (late Oligocene-middle Miocene species D. macinnesi), Micropithecus (middle Miocene species M. clarki and M. leakeyorum), and Simiolus (early middle Miocene species S. enjiessi). They possessed significant sexual dimorphism in size, and their dental formula was 2/2 (incisors), 1/1 (canines), 3/3 (premolars), 3/3 (molars) = 34 teeth. Their canines were strongly bilaterally compressed, their limb bones were slender, and the humerus had a relatively straight shaft.

The African genus Dendropithecus, the most typical dendropithecid, lived 25 to 17 million years ago. It was a small to medium-sized anthropoid, approximating to macaques and gibbons in size (5-9 kg in weight). Its individuals were active, arboreal, quadrupedal Primates, capable of powerful climbing activities and with at least some degree of forelimb suspension. Many traits resemble Proconsul, with which they seem to be closely related. The 20- to 19-million-year-old genus Micropithecus was a small dendropithecid 3 to 4 kg in weight and more adapted to a folivorous diet. Finally,Simiolus was the other small African dendropithecid (4-7 kg in weight) that lived 18 to 16.5 million years ago. It had a face shorter than that of other dendropithecids, and like them, its individuals were arboreal and quadrupedal. It is closely related to Dendropithecus but also probably to the proconsulid Rangwapithecus.

Many of the dendropithecid characteristics can be interpreted as being primitive traits of the catarrhines. The primitive pliopithecoid Kamoyapithecus seems to be related to the dendropithecids. Therefore, they are surely an intermediate group between primitive propliopithecoidpliopithecoids and more modern proconsuloids.

Proconsuloids

Proconsuloids have been considered for a long time to be the earliest probable members of the family Hominoidea. Nevertheless, many paleoprimatologists and paleoanthropologists prefer to consider them, at the moment, within a separate family, the family Proconsuloidea. It comprises taxa that range in size from small chimpanzees to small gorillas. They were members of a major radiation of catarrhines that occurred during the early Miocene, which resemble modern species. The Miocene climate became warmer and drier than the previous cool Oligocene, and the African collision with Europe allowed faunal dispersion from Africa to Eurasia. New, more modern anthropoids, such as the proconsuloids, appeared. Proconsuloids have postcranial skeleton traits more derived than those of their probable ancestors, the dendropithecoids, mainly in the fore-limbs. Their dental formula was 2/2 (incisors), 1/1 (canines), 2/2 (premolars), 3/3 (molars) = 32 teeth, that is, with a reduced premolar compared with the dendropithecoids.

The superfamily Proconsuloidea includes African Arabian taxa and is composed of two families: Proconsulidae and Griphopithecidae. They are often placed in the superfamily Hominoidea because they share derived dental features with the modern great apes. Nevertheless, many paleoprimatologists have questions considering whether they are hominoids because they lack apelike features in the postcranial skeleton, such as the elbow, shoulder, hip, and knee joints.

The family Proconsulidae is subdivided into three subfamilies: Proconsulinae, Afropithecinae, and Nyanzapithecinae. It is accepted that the proconsulines are the most primitive and evolved from afropithecines to nyanzapithecines. The first subfamily has two known genera: Morotopithecus (early Miocene species M. bishopi) and Proconsul (early Miocene species P. africanus, P. nyanzae, P. major, and P. heseloni). The 21- to 15-million-year-old genus Morotopithecus was a large-sized catarrhine (35-55 kg in weight) and comparable to Proconsul major in dental size but possibly smaller in body size. The femoral and phalangeal bones are similar to Proconsul, suggesting an arboreal habit. Morotopithecus has been considered as a possible ancestor of the hominoids based on the presence of shared, derived characteristics of the postcranial skeleton, particularly the lumbar vertebra, linking it with extant apes. The genus Proconsul is the best known proconsulid, and its species lived in the rain forests of Africa between 20 and 17 million years ago. They were medium-sized anthropoids with a range in weight from 10 to 40 kg and up to 60 kg in weight in Proconsul major. They have thin tooth enamel, a light build with narrow chest, short forelimbs, and sexual dimorphism in their teeth (mainly in canines). Their brain was slightly larger than the brains of other catarrhines, except for the hominoids. For example, the brain capacity of P. africanus was approximately 170 cm3. They were arboreal, quadrupedal, and frugivorous. Unlike other Proconsul species, P. nyanzae might have lived in a dry, open woodland environment. P. major is considered to be the probable ancestor of Afropithecus.

The subfamily Afropithecinae has five genera known to date: Heliopithecus (early middle Miocene species H. leakeyi), Nacholapithecus (middle Miocene species N. kerioi), Equatorius (middle Miocene species E. africanus), Afropithecus(early middle Miocene A. turkanensis), and Otavipithecus (middle Miocene O. namibiensis). The most representative member of the subfamily is Afropithecus, an African Arabian proconsulid that lived 18 to 16 million years ago. Except forP. major, it was generally larger than Proconsul (about 20-50 kg in weight) and possessed a long, narrow snout and small eye orbits. Based on its teeth, it is known that its diet consisted of nuts, as well as frugivorous and herbivorous foodstuffs. Its individuals were arboreal and quadrupedal. They had affinities with Heliopithecus, and their distinctive teeth morphology aligns them toward the kenyapithecid-hominoid lineage. The 17- to 16-million-year-old genus Heliopithecus was smaller than Afropithecus, with premolars relatively large compared with Afropithecus and Proconsul. It seems to be related to the proconsulid Morotopithecus, which differs in its dental morphology. Heliopithecus is surely the most primitive afropithecin. The 15- to 14-million-year-old genus Nacholapithecus was a medium-sized afropithecine about 11 to 22 kg in weight. It had proportionally large forelimbs and long pedal digits, suggesting it was a good climber adapted to an arboreal life. The 15.5- to 14-million-year-old genus Equatorius, approximately 25 to 30 kg in weight, is also related to Kenyapithecus. It was more terrestrial than Afropithecus. The 13- to 12-million-year-old genus Otavipithecus was another large-sized (14-20 kg in weight) arboreal, quadrupedal primitive proconsuloid. It has certain mandibular similarities with the griphopithecid Kenyapithecus and even the hominoid Sivapithecus, although it seems to be an afropithecid.

The subfamily Nyanzapithecinae differs from other proconsulids mainly by the dental morphology (molars and premolars). It has four known genera: Nyanzapithecus (early middle Miocene species N. vancouveringorum, N. pickfordi, and N. harrisoni), Mabokopithecus (middle Miocene M. clarki), Rangwapithecus (Miocene species R. gordoni), and Turkanapithecus (early Miocene species T. kalakolensis). The 18.5- to 13-million-year-old genus Nyanzapithecus was a small to medium-sized proconsulid, being 6 to 11 kg in weight. The three species ofNyanzapithecus seem to represent a phyletic series of increasing specialization from early Miocene N. vancouveringorum through N. pickfordi to N. harrisoni in the middle Miocene. Another proconsulid, the 16- to 15-million-year-old Mabokopithecus, was smaller than Nyanzapithecus; both genera are closely related. The 18- to 16.5-million-year-old genus Turkanapithecus had a body size comparable to the modern colobus, being approximately 10 kg in weight, with a face relatively shorter than the other proconsulids. Its individuals were typically arboreal, quadrupedal proconsulids but possibly with enhanced climbing capabilities. The oldest proconsulid was the 20- to 19-million-year-old Rangwapithecus, which had a similar morphology to Proconsul and like it was also arboreal. It was a rain-forest-dweller proconsulid of medium size, being about 15 kg in weight, whose dental morphology suggests a folivorous diet.

The family Griphopithecidae, also called Kenyapithecidae, has been often included within the superfamily Hominoidea since it is the proconsuloid group with more ties to the apes. Whether the representatives of proconsulids or afropithecids can be considered the earliest hominoids still remains problematic, but the griphopithecids, or kenyapithecids, seem to be the basal group from which the earliest hominoids originated. The family Griphopithecidae comprises two African genera, Kenyapithecus (middle Miocene species K. wickeri) and Griphopithecus (middle Miocene species G. darwini, G. alpani, and G. africanus), and perhaps also includes a third genera, Samburupithecus (late Miocene species S. kiptalami). Kenyapithecus is a significant griphopithecid that lived 14 million years ago. Its dental morphology is similar to that of the modern Old World monkeys. It has macaquelike limbs adapted for a knuckle-walking mode of semiterres-trial locomotion. These individuals probably inhabited drier, more open woodland environments. Kenyapithecus had thicker molar enamel, a more robust mandible, and large upper premolars compared with those of the early Miocene proconsulids. Some paleoprimatologists suggest that this taxon is the common ancestor of all the great apes (hominoids), but others consider that it is more primitive and only slightly more modern than Proconsul. The 17- to 16-million-year-old genus Griphopithecus is poorly known, but it was a large European proconsuloid closely linked to the African Kenyapithecus, although probably more primitive. The 11- to 10-million-year-old genus Samburupithecus resembles modern African apes, and some paleoprimatologists have suggested that it is also close in morphology to the possible ancestor of hominoids.

Hominoids

The superfamily Hominoidea comprises the small and great apes, which are agile climbers of trees except for gorillas and humans. They are omnivorous, with a diet mainly consisting of fruits, sees, and leaves, although in most cases some quantities of meat and invertebrates are included. Except for humans, which have spread to all parts of the world, the hominoids are native to Africa and Asia. Most species have a tropical rain forest habitat.

All members of this superfamily have a large braincase. Except for humans, most have a prominent face and prognathous jaw, that is, their mandible protrudes farther out than the maxilla, and their nostrils are close together and face forward and downward. The dental formula is the same for all hominoids: 2/2 (incisors), 1/1 (canines), 2/2 (premolars), 3/3 (molars) = 32 teeth. Generally, their incisors are broad, and their canines are never developed into tusks. Nevertheless, their size varies greatly among species, being especially large in gorillas and markedly small in humans. The small size of human teeth and jaws could be adaptations due to eating cooked food, which may have begun as far back as millions of years ago. Unlike the hylobates, the pongids and hominids are larger Primates with great sexual dimorphism, the males being on average larger and stronger than the females. Nevertheless, the degree of sexual dimorphism varies greatly from species to species.

Although the evolutionary history of the hominoids is poorly known, it is accepted that the earliest fossil apes can be linked to the modern hylobates. In contrast to the paucity of available fossils of hominoids over the past 5 million years, there is much evidence from the Miocene (23-5 million years ago). This fossil record shows that hominoids were much more common and diverse than they are today. The superfamily Hominoidea includes five families, three of them extant, Hylobatidae (gibbons), Pongidae (orangutans), and Hominidae (humans, chimpanzees, and gorillas), and two extinct, Oreopithecidae and Dryopithecidae. Other classifications also include orangutans in the hominids, using the names Ponginae and Homininae to subdivide Hominidae into two subfamilies. Molecular-clock analyses suggest that the hylobates and the pongid-hominid clade diverged about 18 million years ago, and pongids and hominids diverged from each other about 14 million years ago. These molecular data would be consistent whether or not the 17- to 14-million-year-old proconsuloid family Griphopithecidae, or Kenyapithecidae, is included within the superfamily Hominoidea as its basal group. Probably the entire superfamily Proconsuloidea should be included within the hominoids, which has been often proposed, since the 21- to 15-million-year-old Morotopithecus seems to be very near to the probable ancestor of the hylobates, whereas the kenyapithecids could be ancestors of the rest of the hominoid families.

Hylobatids

The hylobates are the small or lesser apes of the family Hylobatidae, extensively known as gibbons and siamangs. They are smaller than the great apes, and their anatomical characteristics are superficially closer to the monkeys than they are to the great apes. They have long hands and feet, and their fur is usually black, gray, or brownish, often with white markings on the hands, feet, and face. Hylobate skulls resemble those of the rest of the hominoids (short rostra, enlarged braincase, and large orbits that face forward). Generally, they do not exhibit sexual dimorphism, with males and females being very similar in size and shape. Nevertheless, some gibbon species have sexual dichromatic differentiation in the male and female fur. They are social animals and strongly territorial, defending their boundaries with vigorous visual and vocal displays. They are habile in their primary mode of locomotion, that is, brachiation, swinging from branch to branch for distances of up to 15 m. They are the fastest and most agile of all tree-dwelling, nonflying mammals. Their diet consists mainly of fruits but also includes insects and leaves.

The hylobates appeared in the middle Miocene and include four extant genera, Hylobates, Nomascus, Symphalangus, and Hoolock, although some taxonomists consider that these are merely four species of only one genus, Hylobates. The genus Hylobates includes several species of Southeast Asia gibbons (H. lar, H. moloch, H. pileatus, H. agilis, H. muelleri, and H. klosii), which often have a ring of white fur around their face, and a size range of 40 to 70 cm in height and 5 to 8 kg in weight. The genus Nomascus includes six species of southeastern Asia gibbons (N. concolor, N. leucogenis, N. siki, N. nasutus, N. hainani, and N. gabriellae), some black with a distinct black tuft of crown fur (black crested gibbons) and some with distinct light-colored cheek patches (white-cheeked and yellow-cheeked gibbons). The genus Symphalangus includes the siamangs (S. syndactylus) of Thailand, Malaysia, and Sumatra; they are larger (twice the size of other gibbons, reaching 1 m in height and 23 kg in weight), with two fingers fused together on each hand, and they have large gular sacs (which can be inflated to the size of their heads to make loud resonating calls or songs). The genus Hoolock includes the hoolocks or hoolock gibbons (H. hoolock and H. leuconedys) of northeast India, Bangladesh, southwest China, and Myanmar; they reach a size of 60 to 90 cm in height and 6 to 9 kg in weight, and they are the only gibbons that have sexual dimorphism (males are black colored with considerably white brows, and females have a grey-brown fur, which is darker at the chest and neck). There is another gibbon genus called Bunopithecus, which includes the extinct species B. sericus, discovered in China but found all over southern Eurasia. The two hoolock species were once included in this genus, but they have recently been removed from Bunopithecus to be grouped in the genusHoolock.

Dryopithecids

The family Dryopithecidae comprises the best-known European fossil hominoids, but they also lived in eastern Africa and Asia. Their dental morphology is roughly intermediate between the early Miocene proconsulids (e.g., Proconsul) from Africa and the later pongids (e.g., Sivapithecus) from Asia. They had thin rather than thick enamel in their cheek teeth, gracile canines, narrow incisors, relatively short premaxilla, and a relatively gracile mandible. Their dental formula was 2/2 (incisors), 1/1 (canines), 2/2 (premolars), 3/3 (molars) = 32 teeth. They resemble the hominoids in many cranial features, including the development of a supraorbital ridge. Their postcranial skeleton is similar to the pongids (e.g., modern orangutans), indicating that they were suspensory. They may include the ancestor of all hominoids, which include the lesser apes (gibbons and siamangs), the great apes or pongids (orangutans, gorillas, chimpanzees, and bonobos), and humans. Many paleoanthropologists consider that the dryopithecids are, in fact, in the evolutionary direction toward hominids.

Dryopithecids include two known genera, Pierolapithecus (middle Miocene species P. catalaunicus) and Dryopithecus (early late Miocene species D. wuduensis, D. fontani, D. brancoi, D. laietanus, and D. crusafonti), and perhaps also include Udabnopithecus (late Miocene species U. garedziensis). Dryopithecus, the most well-known dryopithecid, lived 13 to 7 million years ago in Europe and Asia; these individuals were about 70 to 120 cm in length and 35 kg in weight. They had a 150-cm3 brain capacity, large eye orbits, and a light supraorbital ridge. The face exhibited certain klinorhynchy, that is, the face tilted downward in profile. They were brachiators, like modern orangutans and gibbons, but were never knuckle-walkers like chimpanzees and gorillas. They were tree-dwelling apes that ate berries and fruits. Dryopithecus laietanus, also called Hispanopithecus laietanus, seem to be more like orangutans than the other apes, with very long forelimbs and relatively short femora. The 13-million-year-old genus Pierolapithecus is closely related to the common ancestor of pongids and hominids. They were 30 to 35 kg in weight and 120 m in length and had a wide, flat rib cage, a stiff lower spine, flexible wrists, and shoulder blades that lay along the back. These are special adaptations for tree climbing, just like those found in the great apes of today. The 8.8-million-year-old genus Udabnopithecus is an interesting fossil since it could be a link between the dryopithecids and pongids in Eurasia. Its individuals inhabited a semiarid environment.

Oreopithecids

The family Oreopithecidae includes a single known fossil genus, Oreopithecus, which is represented by only one known species, O. bambolii. Oreopithecus evolved in isolation, over at least 2 million years, on an island in the Mediterranean where Tuscany (Italy) is found today. It lived between 10 and 8 million years ago (late Miocene) in a swampy habitat and adapted to both suspensory arborealism and bipedalism. Oreopithecus was 30 to 35 kg in weight and 1.10 to 1.20 m in height. Its skull possessed a small and globular neurocranium, with a cranial capacity between 275 and 530 cm3. Moreover, it had a relatively short snout, elevated nasal bones, vertical orbital plane, gracile facial bones, a large attachment surface for the masseter muscle, and a sagittal crest, indicating a heavy masticatory apparatus. Its canines had a size comparable to the rest of its dentition. Its postcranial anatomy was characterized by a broad thorax, a short trunk, and long fingers. It had a lumbar curve, suggesting that it adapted to upright walking. Because of these characteristics, this species is a considerable anomaly since it represents an independent development of bipedality, and its taxonomic placement is unsettled. Most paleoanthropologists consider it an extinct great ape without descendants, perhaps derived from Dryopithecus just before the split from the orangutans. Some paleoanthropologists include the oreopithecids within the family Dryopithecidae as a very derived group.

Pongids

The family Pongidae contains several genera, and all but one are now extinct. The extant genus is Pongo (orangutans) with two known species: P. pymaeus and P. abelii. They are native to Indonesia and Malaysia, being Pongo pymaeusfrom the island of Borneo and Pongo abelii from the island of Sumatra.

Orangutan skulls have a prominent sagittal crest, which is a ridge of bone running lengthwise along the midline of the top of the skull at the sagittal suture, whose presence indicates that there are exceptionally strong jaw muscles (mainly temporal muscles, which are one of the main chewing muscles). Orangutan brain capacity is 275 to 500 cm3. Orangutans are large apes and exhibit considerable sexual dimorphism in size, with the P. abelii adult males 1.65 to 1.75 m in height and 90 to 120 kg in weight and the adult females 1.25 to 1.35 m in height and 40 to 50 kg in weight. P. pymaeus individuals are smaller, with adult males 1.30 to 1.40 m in height and 50 to 100 kg in weight and adult females 1.10 to 1.20 m in height and 35 to 45 kg in weight. Their arms, which can grow up to 2 m in length, are twice as long as their legs. Their feet are designed like hands, and both their hands and feet are long, narrow, and strong, being used in a hooklike fashion when grasping branches. Their thumbs are fully opposable. Orangutans are quadrupedal when on the ground, but unlike chimpanzees and gorillas, they are not true knuckle-walkers; they walk on the ground by shuffling on their palms with their fingers curved inward. Males have secondary sexual characteristics, such as long fur, cheek pads, and a throat pouch.

Orangutans are arboreal dwellers, spending nearly all of their time in the trees, living typically in tropical-subtropical moist broadleaf forests. They are mainly frugivorous. Sumatran orangutans (P. abelii) are more frugivorous and especially more insectivorous than the Bornean orangutans (P. pymaeus). The Borneo orangutans have a more varied diet, which includes leaves, shoots, seeds, birds’ eggs, insects, and bark. Their gestation period is 8.5 months, and their life span is between 35 and 40 years. The individuals are sexually mature at the age of 6 to 7 years. They are infants from 0 to 4 years, juveniles from 4 to 7 years, adolescent males from 7 to 10 years, and adolescent females from 7 to 12 years. Several genetic differences separate the two species of orangutan (P. abelli and P. pymaeus). The species parted from one another 2.3 million years ago. The DNA sequences of humans and orangutans differ in only 3.6% of their genomes, that is, in their complete DNA sequences, suggesting that pongids and hominids (the orangutan-gorilla-chimpanzee-bonobo and human group) diverged about 10 to 11 million years ago. Like the other great apes, orangutans are very intelligent, being capable of using feeding tools. Some psychology specialists consider that the orangutan is the most intelligent extant animal in the world other than the human being; therefore, the orangutan is more intelligent than the chimpanzee, bonobo, or gorilla. They have developed a great symbolic capability and even a complex culture in which adult orangutans teach younger ones how to make tools and find food.

The family Pongidae comprises two subfamilies, Palaeoponginae and Ponginae, which include preponderantly fossil species. The subfamily Palaeoponginae includes four known genera: Rudapithecus (late Miocene species R. hungaricus), Bovdapithecus (late Miocene species B. altipalatus), Graecopithecus (late Miocene species G. freybergi), andOuranopithecus (late Miocene species O. macedoniensis). The 11- to 10-million-year-old genera Rudapithecus and Bovdapithecus were palaeopongines of 45 to 60 kg in weight and have been considered closely related to the dryopithecids. The 10- to 8-million-year-old genus Graecopithecus shows the downwardly bent face (klinorhynchy) typical of African apes and also very thick molar enamel, as expected in an early hominid. The 10- to 8-million-year-old genus Ouranopithecus was a larger-sized pongid, with males probably between 80 and 100 kg in weight. It also has intermediate traits between the dryopithecids and the pongids. It has a large, broad face with a prominent supraorbital ridge and square-shaped eye orbits and exhibits clear sexual dimorphism. Some paleoanthropologists have considered that it also has a relationship with hominids, particularly with gorillas. Graecopithecus and especially Ouranopithecusmay lie near the split between the Pongidae and the Hominidae or already be in the hominid lineage.

The subfamily Pongidae includes three Asian groups, two extinct (Lufengpithecini and Sivapithecini) and one extant (Pongini). The group Lufengpithecini is apparently the most primitive. It includes two genera: Lufengpithecus (late Miocene species L. lufengensis, L. keiyuanensis, and L. hudienensis) and Ankarapithecus (late Miocene species A. meteai). The 8- to 7-million-year-old genus Lufengpithecus was a large pongid about 50 kg in weight, with slightly greater sexual dimorphism than in living apes. Its cranial characteristics show greater similarities to Dryopithecus, such as a broad interorbital region, vertical frontal, and the lack of a broad interorbital torus. The 10-million-year-old genus Ankarapithecus appears to be intermediate between the dryopithecids-paleopongines and the sivapithecins. Lufengpithecinis are considered a primitive sister group to the clade formed by the sivapithecini and pongini, with Ankarapithecus more closely related to this clade.

The group sivapithecini includes two genera: Sivapithecus (middle late Miocene species S. brevirostris, S. punjabicus, S. indicus, S. sivalensis, and S. parvada) and Gigantopithecus (late Miocene-middle Pleistocene species G. blacki, G. giganteus, and G. bilaspurensis). The genus Sivapithecus was an arboreal pongid that lived between 13 and 8.5 million years ago. It was the size of a chimpanzee (50-90 kg in weight), but with the facial morphology of an orangutan. It shows facial, palatal, and dental architectures clearly specialized in the orangutan direction. However, unlike the great apes, Sivapithecus lacks the complex arm-bone features related to suspensory behavior and forelimb flexibility, suggesting the pongid was more adapted to quadrupedalism. The genus Gigantopithecus was a huge, herbivorous ape that lived between 1 and 0.3 million years ago in southeastern Asia. Its specimens represent the largest apes that ever lived, reaching 1.8 to 3 m in height and about 250 to 550 kg in weight, the largest being three times heavier than a modern gorilla. They coexisted with Homo erectus in Asia, and some cryptozoologists have related them to legendary Primates like Yeti and Bigfoot.

The group Pongini includes two genera: the fossil Khoratpithecus (late Miocene species K. chiangmuanensis and K. piriyai) and the above-mentioned extant Pongo (from middle Pleistocene to Recent). The 9- to 7-million-year-old genus Khoratpithecus shares unique derived characteristics with orangutans, supporting the close relationships of both taxa. It was a large ape of approximately 0.9 to 1.2 m in height and 40 to 80 kg in weight. Its traits suggest that it is an intermediate between Lufengpithecus and modern Pongo. The genus Pongo originated during the Pleistocene 2 million years ago. Although modern Pongo are currently found only on Borneo and Sumatra, the Pongo fossil record indicates that orangutans once had a wider distribution, also having been found in Java, Vietnam, and China. A 1-million-year-old fossil species, Pongo hooijeri, is known from Vietnam, and several Pleistocene fossils of extant species have been described from southeastern Asia.

Hominids

The earliest evolution of the hominids is not well-known, with the notable exception of humans, which have a relatively complete fossil record extending back more than 4 million years. The evolutionary history of the pongids is, by comparison, much better documented. Most hominid species are omnivorous, but their feeding base is vegetarian (mainly fruits). The smallest living species of hominids is the bonobos (Pan paniscus), also known as pygmy chimpanzees, weighing 30 to 40 kg. The largest ones are the gorillas, with males weighing 140 to 180 kg.

The family Hominidae is subdivided into two subfamilies: Gorillinae and Homininae. The first one includes the genus Gorilla and a recently discovered fossil genus, Chororapithecus (late Miocene species C. abyssinicus). The genus Gorilla includes two extant species: G. gorilla and G. beringei. The first are known as the western gorillas (living in the Republic of Congo, Gabon, Equatorial Guinea, and Cameroon), the most populous species of gorillas, while the second ones are the eastern gorillas (living in the eastern Congo, Kinshasha, Uganda, and Rwanda).

Gorillas are the largest of the living Primates with great sexual dimorphism in size, the adult males 1.65 to 1.80 m in height and 140 to 210 kg in weight and the adult females 1.35 to 1.45 m in height and 90 to 120 kg in weight. The cranial capacity of gorillas is 340 to 750 cm3. The eastern gorilla (Gorilla beringei) is more darkly colored than the western gorilla (Gorilla gorilla). Gorilla skulls have a prominent mandibular prognathism and a great supraorbital ridge and a prominent sagittal crest. The gestation period of the gorillas is 8.5 months. Infants stay with their mothers for 3 to 4 years, and the females mature sexually at 10 to 12 years and males at 11 to 13 years. Their life span is between 30 and 50 years. Gorillas, like chimpanzees, move around quadrupedally by knuckle-walking. They are fundamentally herbivores, eating leaves (foliovores) but also fruits and shoots. Their large sagittal crest and long canines allow them to crush hard plants. Nevertheless, some gorillas may ingest small insects. Gorillas are considered highly intelligent, with some individuals in captivity being capable of using a subset of sign language.

The DNA sequences of humans and gorillas differ in about 1.6% of their genes, but in only 2.3% of their genomes, that is, in their complete DNA sequences, thus being the next closest living relative to humans after the chimpanzees. This suggests that the human-chimpanzee clade and the gorilla shared a common ancestor about 8 million years ago. However, a significant fossil species of about 11 to 10 million years ago has been recently discovered: Chororapithecus abyssinicus. Its dental traits strongly indicate that it is the earliest species of the subfamily Gorillinae, suggesting that the last common ancestor between hominines (chimpanzees and humans) and gorillines may have lived more than 10 million years ago, that is, 2 million years earlier than the previously believed date of divergence based on DNA molecular-clock calibrations.

The subfamily Homininae is subdivided into two groups: Panini and Hominini. The group Panini consists of the genus Pan, which includes two extant species commonly named chimpanzees: P. troglodytes and P. paniscus. The first one is the common chimpanzee, which lives in the forests of central and West Africa. The second one is the bonobo, or pygmy, chimpanzee, which lives in the Congo. Pan troglodytes, or the common chimpanzee, is found not only in the tropical forests but also on the savannas of central and West Africa, although its habitat has been dramatically reduced in recent decades. Adults can measure up to 1.60 m in height in males and 1.30 m in females and weigh 40 to 70 kg in males, and 25 to 50 kg in females. The cranial capacity of chimpanzees is 275 to 500 cm3. Except for the face and palms of the hands and soles of the feet, the common chimpanzee body is covered by coarse, dark brown hair. They are omnivorous, eating small prey and insects, but their diet is mainly vegetarian (fruits, seeds, leaves, etc.). Common chimpanzees are both arboreal and terrestrial, their habitual gait quadrupedal although they can walk upright for short distances. They live in communities that range from 20 to more than 150 members in fission-fusion societies (the social groups sleep in one locality together but forage in small groups, going off in different directions during the day). Their gestation period is 8 months and their life span is 40 to 45 years. They are infants from 0 to 4 years, juveniles from 4 to 7 years, adolescent males from 7 to 15 years, and adolescent females from 7 to 13 years in age. The individuals (females and males) mature sexually at 9 to 10 years. It has been long known that the chimpanzees use tools, including modified branches to capture squirrels; recent studies suggest that the chimpanzees made stone tools at least 4 million years ago. It has been shown that they have an incipient consciousness, being manipulative and capable of deception as well as being capable of using symbols and understanding aspects of human language.

Bonobos (Pan paniscus) are smaller and more gracile than common chimpanzees, 75 to 85 cm in height and 35 to 45 kg in weight in adult males, and 70 to 75 cm in height and 25 to 35 kg in weight in adult females. They have brow ridges above the eyes less prominent than those of the common chimpanzees and black faces with pink lips, small ears, wide nostrils, and long hair on their heads. They walk upright about 25% of the time during ground locomotion. Their physical characteristics (slim upper body, narrow shoulders, thin neck, and long legs when compared with the common chimpanzees) and posture give the bonobos an appearance more closely resembling humans. Bonobos are mainly frugivorous, but they supplement their diet with leaves, meat of small vertebrates, and invertebrates.

The DNA sequences of the human and the common chimpanzee are very similar, differing about 2.7% in their genes and only 1% in their genomes. This suggests that humans and chimpanzees are more closely related than humans are with the gorillas, and they shared a common ancestor about 5 to 6 million years ago. Moreover, DNA molecular-clock evidence also suggests that Pan troglodytes and the other chimpanzee species Pan paniscus (bonobos) separated from each other less than 1 million years ago. It’s possible that the formation of the Congo River 1.5 to 2 million years ago led to the speciation of P. paniscus. Until recently, no fossils of chimpanzees had been found. However, middle late Pleistocene fossils found in Uganda and Kenya may become the first fossils of the genus Pan.

Finally, the group Hominini includes seven known genera: Sahelanthropus, Orrorin, Ardipithecus, Australopithecus, Paranthropus, Kenyanthropus, and Homo, of which only the last one has extant species, our own (Homo sapiens). It is notable that the 7.4- to 6-million-year-old genus Sahelanthropus has been considered the last common ancestor of Pan and Homo. The hominin lineage has a trend toward a larger and more developed brain, shorter legs and arms, and ever more complex social behavior, intelligence, and technology. The description, fossil record, and evolutionary history of this hominid group are analyzed in the chapter “Hominid Description.”