LECTURE 2: BEFORE HOMO
The evolutionary history of the primates can be traced back for some 85 million years, as one of the oldest of all surviving placental mammal groups. Most paleontologists consider that primates share a common ancestor with the bats,[citation needed] another extremely ancient lineage, and that this ancestor probably lived during the late Cretaceous, together with the last dinosaurs. The oldest known primates come from North America, but they were widespread in Eurasia and Africa as well, during the tropical conditions of the Paleocene and Eocene.
With the beginning of modern climates, marked by the formation of the first Antarctic ice in the early Oligocene around 40 million years ago, primates went extinct everywhere but Africa and southern Asia. One such primate from this time was Notharctus. Fossil evidence found in Germany 20 years ago was determined to be about 16.5 million years old, some 1.5 million years older than similar species from East Africa.[6] It suggests that the primate lineage of the great apes first appeared in Eurasia and not Africa .
The discoveries suggest that the early ancestors of the hominids (the family of great apes and humans) migrated to Eurasia from Africa about 17 million years ago, just before these two continents were cut off from each other by an expansion of the Mediterranean Sea. Begun[6] says that these primates flourished in Eurasia and that their lineage leading to the African apes and humans—Dryopithecus—migrated south from Europe or Western Asia into Africa. The surviving tropical population, which is seen most completely in the upper Eocene and lowermost Oligocene fossil beds of the Fayum depression southwest of Cairo, 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.
The earliest known catarrhine is Kamoyapithecus from uppermost Oligocene at Eragaleit in the northern Kenya rift valley, dated to 24 mya (millions of years before present). Its ancestry is generally thought to be close to such genera as Aegyptopithecus, Propliopithecus, and Parapithecus from the Fayum, at around 35 mya. There are no fossils from the intervening 11 million years. No near ancestor to South American platyrrhines, whose fossil record begins at around 30 mya, can be identified among the North African fossil species, and possibly lies in other forms that lived in West Africa that were caught up in the still-mysterious transatlantic sweepstakes that sent primates, rodents, boa constrictors, and cichlid fishes from Africa to South America sometime in the Oligocene.
In the early Miocene, after 22 mya, many kinds of arboreally adapted primitive catarrhines from East Africa suggest a long history of prior diversification. Because the fossils at 20 mya include fragments attributed to Victoriapithecus, the earliest cercopithecoid; the other forms are (by default) grouped as hominoids, without clear evidence as to which are closest to living apes and humans. Among the presently recognized genera in this group, which ranges up to 13 mya, we find Proconsul, Rangwapithecus, Dendropithecus, Limnopithecus, Nacholapithecus, Equatorius, Nyanzapithecus, Afropithecus, Heliopithecus, and Kenyapithecus, all from East Africa. The presence of other generalized non-cercopithecids of middle Miocene age from sites far distant—Otavipithecus from cave deposits in Namibia, and Pierolapithecus and Dryopithecus from France, Spain and Austria—is evidence of a wide diversity of forms across Africa and the Mediterranean basin during the relatively warm and equable climatic regimes of the early and middle Miocene.
The youngest of the Miocene hominoids, Oreopithecus, is from 9 mya coal beds in Italy.
Molecular evidence indicates that the lineage of gibbons (family Hylobatidae) became distinct between 18 and 12 Ma, and that of orangutans (subfamily Ponginae) at about 12 Ma; we have no fossils that clearly document the ancestry of gibbons, which may have originated in a so far unknown South East Asian hominid population, but fossil proto-orangutans may be represented by Ramapithecus from India and Griphopithecus from Turkey, dated to around 10 Ma.
It has been suggested that species close to last common ancestors of gorillas, chimpanzees and humans may be represented by Nakalipithecus fossils found in Kenya and Ouranopithecus found in Greece. Molecular evidence suggests that between 8 and 4 mya, first 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.[7] The fossil record of gorillas and chimpanzees is quite limited [8]. Both poor preservation (rain forest soils tend to be acidic and dissolve bone) and sampling bias probably contribute to this problem.
Other Hominines, however, likely adapted (along with antelopes, hyenas, dogs, pigs, elephants, and horses) to the somewhat drier environments outside the equatorial belt (which contracted after about 8 million years ago; reference needed) and their fossils are relatively well known. The earliest are Sahelanthropus tchadensis (7–6 mya) and Orrorin tugenensis (6 mya), followed by:
- Ardipithecus (5.5–4.4 mya), with species Ar. kadabba and Ar. ramidus;
- Australopithecus (4–2 mya), with species Au. anamensis, Au. afarensis, Au. africanus, Au. bahrelghazali, and Au. garhi;
- Kenyanthropus (3-2.7 mya), with species Kenyanthropus platyops
- Paranthropus (3–1.2 mya), with species P. aethiopicus, P. boisei, and P. robustus;
- Homo (2 mya–present), with species Homo habilis, Homo rudolfensis, Homo ergaster, Homo georgicus, Homo antecessor, Homo cepranensis, Homo erectus, Homo heidelbergensis, Homo rhodesiensis, Homo sapiens neanderthalensis, Homo sapiens idaltu, Archaic Homo sapiens, Homo floresiensis
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