TUKUL 3: Palaeoanthropology

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Proconsul heseloni

Before Homo

The evolutionary history of the primates can be traced back for some 85 million years. The oldest primates are known from North America, but they were widespread in Eurasia and Africa as well, during the tropical conditions of the Palaeocene and Eocene. With the beginning of modern climates, marked by the formation of the first Antarctic ice in the early Oligocene around 40 Myr, primates extinguished everywhere with the exception of Africa and southern Asia.

The discoveries suggest that the early ancestors of the Hominids migrated to Eurasia from Africa about 17 Myr, just before these two continents were cut off from each other by an expansion of the Mediterranean Sea.

Location of Rusinga Island, Kenya
The surviving tropical population gave rise to all living primates—lemurs of Madagascar, lorises of Southeast Asia, galagos or "bush babies" of Africa, and the anthropoids; platyrrhines or New World monkeys, and catarrhines or Old World monkeys and the great apes and humans. In the early Miocene, after 22 Myr, many kinds of arboreal adapted primitive catarrhines from East Africa suggest a long history of prior diversification. Among the presently recognized genera in this group, which ranges up to 13 Myr, we find Proconsul from East Africa. The youngest of the Miocene hominoids, Oreopithecus, is known from 9 Myr coal beds in Italy. Molecular evidence indicates that the lineage of gibbons (family Hylobatidae) became distinct between 18 and 12 Myr, that of orang-utans (subfamily Ponginae) at about 12 Myr. Between 8 and 4 Myr, the gorillas and then the chimpanzee (genus Pan) split off from the line leading to the humans. Human DNA is 98.4 percent identical to the DNA of chimpanzees. We have no fossil record, however, of either groups of African great apes, possibly because bones do not fossilize in rain forest environments.

Proconsul heseloni

Proconsul, from the Early and Middle Miocene of East Africa, is widely regarded as the most primitive representative of the Hominoidea. However, a review of the historical development of this viewpoint shows that the proposed relationship of Proconsul to extant hominoids has long been an unquestioned assumption without adequate evidence. There appears to be relatively few characters that can be advanced in support of such a phylogenetic link. Relative brain size in Proconsul heseloni can be shown to be close to the mean value for extant anthropoids. Also, given the range of diversity seen in modern anthropoids, it would appear that the degree of encephalization is of limited utility as a character in phylogenetic analysis, and can be shown to be much more intimately correlated with behavioral or ecological attributes, such as diet. On the other hand, there are a number of derived cranial and postcranial characters shared by all extant catarrhines that are absent in Proconsul. In addition, extant catarrhines share a number of important derived features of the cranial base and facial skeleton, whereas Proconsul retains a more primitive platyrrhine-like morphology in these respects. One can conclude from these new observations that Proconsul is not a primitive hominoid, as has generally been inferred, but is rather a stem catarrhine that diverged prior to the last common ancestor of all extant members of the Catarrhini.

Proconsul heseloni - 14 Myr


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