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CENOZOIC ERA

NEOGENE PERIOD

Miocene Epoch

23-5 million years ago

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apesapeape

A great variety of apes evolved in the Miocene, including the bipedal Oreopithecus.

During the Miocene, apes experienced their greatest radiation with as many as 30 species existed, inhabiting broad regions of Africa, Asia, and Europe. During the Late Miocene, climatic changes that increased seasonality (and gradually replaced many forests with grasslands) and competition from an ever increasing number of monkey species caused a decline in the diversity of ape species (Gibbons, 1997). The primitive apes Nacholapithecus (15 million years ago) and Proconsul (18 million years ago) lacked tails, indicating that the loss of the tail was one of the first modifications in ancestral apes (Natatsuka, 2004; Ishida, 2004).


Proconsul is an ape known from Uganda and Kenya from 22-17 million years ago. Postcranially, it was more similar to apes than monkeys and had several apelike jaw and tooth characteristics. Its thumb was opposable. Some characteristics were similar to those of the hominids (its P3 tooth, the degree of encephalization, the head of its humerus, its trochlea, hallux, ulna, and the absence of a tail). There were a number of species of Proconsul: P. africanus was baboon sized, P. major was largest species and was gorilla sized, and P. hamiltoni which is tentatively dated at 24-27 million years which would make it the oldest ape (Walker, 1983; Caroll, 1988; Andrews, 1992).

Family Proconsulidae includes all Early Miocene apes. It includes the species Dendropithecus, Dionysopithecus (found in Asia), Limnopithecus (whose denticia was similar to that of Proconsul), Micropithecus, and Rangwapithecus. Micropithecus is the smallest known ape (living or fossil) and its face is similar to modern gibbons (Fleagle, 1978). Proconsul and Afropithecus were probably arboreal apes. The modified hands of Nacholapithecus kerioi indicate that it adapted for climbing and was more arboreal than other Miocene apes. Kenyapithecus was more adapted to terrestrial locomotion than other Miocene apes (Nakatsukasa, 2003).

Family Oreopithecidae includes the apes Nyanzapithecus from the Early-Middle Miocene from Africa and Oreopithecus from the late Miocene from Europe. Oreopithecus is a hominoid from the Late Miocene (7-9 million years ago) from Italy. It was bipedal and had a number of hip adaptations which supported this locomotion such as cancellous bone architecture, a long ischial spine, a prominent anterior inferior iliac spine, a short ischium, and a short pubic symphysis (Rook, 1999). Given that both early hominids and Oreopithecus independently evolved bipedality, it is not surprising Oreopithecus hands were modified to improve their grasping ability in ways similar to those observed in early hominids (Moya-Sola, 1999).

Turkanopithecus was a medium-sized ape whose relationships to other groups of apes are not yet clear (Leakey, 1986b).


Some feel that the Family Pliopithecidae is related to the ancestors of gibbons. Laccopithecus is known from the Late Miocene from Asia. Pliopithecus was known from the Middle to Late Miocene from Europe. These apes had 7 lumbar vertebrae compared to 5 in humans and had specialized characters such as lower molar form, sideways orbital openings, and long bones.


Dryopithecus is known from the Mid-Late Miocene from Africa and Europe
23 to 9 million years ago. The legs of Dryopithecus were more derived than those of Proconsul, Morotopithecus, Equatorius/Kenyapithecus, and Sivapithecus (Maclatchy, 2001). It is classified in the clade with the African apes and diverged from the hominid lineage before the last common ancestor of the African apes and humans. Preliminary evidence suggests that its brain size was consistent with that of other great apes (Kordos, 2001; Moya Sola, 1993; Andrews, 1976). It had long arms and short hands and was adapted for swinging at low speeds. Other species in the dryopithecine tribe included Afropithecus, Heliopithecus, Otavipithecus, Kenyapithecus, and Griphopithecus (Leakey, 1986; Benefit, 1995; Ward, 1999)
Gigantopithecus is known from the Middle Miocene to Pleistocene from Asia.
It was associated with woodland habitat and apparently adapted to the Miocene climate change. From its teeth and mandibles, it is the largest ape that ever existed (since teeth are twice the size of gorilla teeth, it may have reached 11-12 feet in height). It coexisted in Asia with Homo erectus (Ciochon, 1996).

Sivapithecus existed in the Mid-Late Miocene from Africa, Asia, and Europe. Many believe it to be ancestral to orangutans (or at least very closely related to their ancestors) on the basis of a number of traits such as maxillary sinus, temporo-mandibular joint, zygomatic bone, temporal bone, facial profile, orbital shape, and palatal shape. Ramapithecus from Eurasia was a species very closely related to Sivapithecus (some feel they are the same genus) (Leakey, 1985; Pilbeam 1977, Pilbeam, 1982; Pilbeam, 1990; Andrews, 1977; Raza, 1983; Walker, 1973; Benefit, 1995).


Fossils of an ancestral chimp femur and a four-million year old gorilla tooth are known (First fossil chimp, 2004).


POSSIBLE HOMINID ANCESTORS AMONG MIOCENE APES
In recent years, more complete skeletons of Dryopithecus and Kenyapithecus have been found which demonstrate closer affinities to the hominids than had previously been described. If Dryopithecus were an ancestor to modern apes, its position would be before the split between African apes and hominids. Kenyapithecus shows signs of being a semi-terrestrial quadruped, perhaps the first to spend significant time on the ground. Kenyapithecus diverged from lineage leading to the higher apes after Proconsul and Griphopithecus but before Sivapithecus. Kenyapithecus africanus, a 27 kg ape from 15 mya, has been renamed Equatorius africanus. It is similar to Proconsul and less derived than Kenyapithecus wickeri (Benefit, 1995; McCrossin 1993; McCrossin 2001; Ward, 1999). Graecopithecus may have been a member of the African ape clade although further analysis is required to determine whether thick tooth enamel is a primitive or derived condition. Humans possess thick enamel on their teeth unlike other African apes which was interpreted to be an adaptation of the human lineage. It now appears that this trait was a primitive condition in higher apes (such as Sivapithecus) which was secondarily lost in gorillas and chimps (Andrews, 1992; Martin 1985).
Morotopithecus was an ape that lived 20 million years ago. Its vertebrae and glenoid cavity similar to modern apes and humans while its proximal femur and other characteristics are primitive. It is more derived than Proconsul and some feel that it is a common ancestor to apes and hominids before orangutan lineage separated (Menon, 1997;. Gebo, 1997) The lumbar vertebrae of Morotopithecus are more similar to those of living apes than are the vertebrae of Proconsul (Sanders, 1994). Morotopithecus seems to be a primitive great ape, more derived than gibbons. If this is true, it means that great ape and gibbon lineages had diverged by 20 million years ago, which is 2 million years earlier that what had previously been thought (Young, 2004).
Ouranopithecus lived 9-10 million years ago. Its canines are smaller than any recent or extinct apes. Its tooth enamel, tooth occlusal pattern, and other characteristics are similar to Australopithecus (de Bonis, 1990; McCrossin, 2001).

Ankarapithecus lived about 9.8 million years ago. Some characters such as the narrow interorbital region, flat zygomatic region, and elongated premaxilla are similar to orangutans. Some characteristics such as a supraorbital torus and frontal sinus are similar to gorillas and chimpanzees (Alpagut, 1996).

Samburupithecus kiptalami was a hominoid about the size of a gorilla known from the upper Miocene of Kenya. In some dental and oral features, it is more similar to primitive fossil apes while in others it is more similar to modern apes and hominids (Ishida, 1997).