APES

MIOCENE  APES      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). While some features of Proconsul (such as its teeth, long arms, mobile shoulder and elbow, gasping toes, lack of an ischial expansion on the hip) were more similar to those of modern apes, other features were more similar to those of Old World monkeys (hip, length of the back, back mobility, narrow trunk, kneecaps, leg, and semicircular canals). Analysis of the sacrum indicates that it lacked an external tail like all modern apes. Proconsul probably weighed 25-30 pounds and was adapted for life in trees. Its teeth suggest that it primarily depended on fruit rather than leaves (Walker, 2005; Kingdon, 2003).

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).   THE APE PELVIS

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; Kohler, 2003). 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.

A 12.5-13 million year old ape fossil named Pierolapithecus may represent the common ancestor of the great apes after the gibbon lineage separated from that of other apes. It might have weighed about 75 pounds and retained a number of primitive ancestral features (Wilford, 2004).       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).

The skulls of fetal and infant apes are more rounded and highly domed than those of adult apes (as evident in the photo of an orangutan fetal skull below). Some have proposed that the development of a more rounded skull in hominids was a retention of a juvenile trait rather than the development of a new one. Fossils of an ancestral chimp femur and a four-million year old gorilla tooth are known (First fossil chimp, 2004). A late Pleistocene femur once classified as human is now thought to represent a chimp fossil (DeSilva, 2006). Genetic analyses indicate that the chimp and human lineages diverged from 5 to 7 million years ago and the ape and Old World monkey lineaged diverged between 24 and 35 million years ago (Kumar, 2005). At functionally important DNA sites, humans and chimp sequences are 99.4% identical while at less important sites, the homology is 98.4% homologous. Of the DNA sequences which can be aligned between the human and chimp genomes, only 1% of the DNA bases differ. Because of the insertions and deletions, the total difference in the genomes is about 4%. Based the extremely close genetic similarity between humans and chimps, it has been argued that chimps should be classified in the genus Homo (Wildman, 2003; Culotta, 2005) Common chimpanzees and bonobos use similar facial and vocal signals. In contrast, gestures are more variable within a species and between the two species and are thus probably under a greater amount of voluntary control. Monkeys use facial and vocal signals but not gestures. It is possible that the use of gestures in apes laid the foundations for human language (Pollick, 2007). Although chimps and other primates have a greater capacity for tool use and language ability than is observed in their wild behavior (Guy, 2006). Tool use occurs in a variety of animals but is most advanced in chimps (Pruetz, 2007). Chimps are the only animals other than humans which habitually use tools to hunt vertebrate animals. Male, female, and immature chimps have been observed to fashion spear-like tools from tree branches to hunt for nocturnal prosimians hiding in the crevices they hide in during the day. Tool preparation can include several steps such as trimming off side branches and trimming the tip of the spear (Pruetz, 2007).  Stone tools have been identified in an African rainforest which date to more than four thousand years old. The structure of the tools and nut remains (which include sources typically used by chimps and others used exclusively by chimps) indicate that these were used by chimps rather than by humans. Modern chimps in the region continue to use rocks for nut cracking, suggesting that this behavior has been passed on for more than 200 generations. The concept of a "Chimpanzee Stone Age" leads to the interesting hypothesis that the use primitive stone tools might have arisen prior to the first hominids (Mercader, 2007). 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). In the Middle Miocene, Kenyapithecus and Equatorius both possessed anatomical features which would allow them to spend more time on the ground. Kenyapithecus possessed modified shoulder muscles and a scapulo-clavicular joint consistent with a semi-terrestrial lifestyle. Although its legs were adapated to vertical climbing, indicating that it spent some time in trees, its arms lacked the adaptations consistent with a hanging lifestyle. The ape Nacholapithecus was adapted for an arboreal lifestyle (Senut, 2003).      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).