The Evolution Of Primate Locomotion And Body Configuration Essay

The Evolution Of Primate Locomotion And Body Configuration - Essay Example In 1956, while searching through a collection of fossils at the American Museum of Natural History, I came across a small piece of forehead bone, identified as a "possible primate," that had lain neglected for half a century. It had been recovered from the Fayum badlands, sixty miles southwest of Cairo, Egypt, by an amateur collector named Richard Markgraf. The rock in which it was found was known to belong to the geological epoch we call the Oligocene (now estimated to have lasted from 34 to 23 million years ago). Although only the size of a quarter, the fossil displayed two defining characteristics of the Anthropoidea, or higher primates--the large evolutionary group that includes monkeys, apes, and humans. I could tell that the right and left frontal (forehead) bones in this small animal were fused along the midline suture into a single bone, as is the case in all the higher primates. And on the right side, just enough of the rim of the eye socket was preserved for me to establish that it was fully enclosed in the back by bony plates (the eyeballs of more primitive primates are normally encircled by just a thin bar of bone). Neither feature had been previously documented in so old a fossil. Better late than never, the small piece of bone joined a short list of other fossils discovered in the Fayum between 1906 and 1910 that also appeared to belong to higher primates. The best of the other fossils--both nearly complete mandibles--belonged to two small species named Parapithecus fraasi and Propliopithecus haeckeli. Both have lower molars with anthropoidean features--in particular, they are broad and flat and have five cusps. (Miyamoto 197-220) In addition, Propliopithecus has the same number of the different types of teeth as other Old World anthropoideans, and the two sides of the lower jaw are solidly fused together in the front, another important characteristic of higher primates. My interest sparked by these tantalizing finds, I began doing fieldwork in the Fayum more than thirty years ago. Since then, my teams and I have succeeded in gathering hundreds of additional primate fossils, documenting the presence of eleven primate species in Oligocene deposits that are 30 to 33 million years old. The largest of these species, a close relative of Propliopithecus, is Aegyptopithecus zeuxis, a cat-size creature that appears to stand at or near the base of the family tree of the Old World monkeys, apes, and humans. We have collected several skulls and faces of Aegyptopithecus, as well as many bones from the rest of its skeleton (see "Dawn Ape of the Fayum," Natural History, May 1984). Many of the eleven Oligocene species have anthropoidean features, including the fused frontal bone, enclosed eye socket, lower jaws that are solidly fused together in the front, and the broadened and flattened lower molars with five principal cusps. In certain details, the upper molars also resemble those of more recent higher primates. Another anthropoidean characteristic is the manner in which the bony ring encircling the eardrum lines the auditory opening at the side of the skull. The eleven species are diverse in many respects, however. By 1985, I had accumulated enough evidence to say that they fell into several different taxonomic families or subfamilies. Given that so much diversity had evolved, I had to conclude that the common ancestor of all the higher primates must go back a long way in Africa. This was only the beginning, however, for in 1983 a Fayum site called Locality 41 had been discovered. Its exposed deposits came from a much deeper layer than those of