Bones of Ground-Based Ape Unearthed - Brief Article

USA Today (Society for the Advancement of Education), June, 2000

ANTHROPOLOGY

The earliest fossil of a groundbased Base ape has been identified by University of Illinois at Chicago researcher Jay Kelley and colleagues at Northeastern Ohio Universities College of Medicine, Yale University, and Northern Arizona University. They have classified the fossil ape as a new hominoid genus from the middle Miocene epoch and named it Equatorius. Recognition of the new genus was prompted by the discovery of the partial skeleton of a fossil ape by a team led by Yale's Andrew Hill and Northeastern's Steve Ward. The skeleton is from an approximately 15,000,000-year-old site at Kipsaramon, in the Tugen Hills of western Kenya.

The limb anatomy of Equatorius indicates that members of this genus were at least partly adapted for life on the ground. Moreover, facial and jaw features were a key in the characterization of the new genus. "Recognizing the distinctiveness of Equatorius provides a more accurate framework to assess the wealth of new fossil material from the middle Miocene that is being uncovered," explains Kelley, the research team's expert on oral anatomy.

Prior to this discovery, the species now included in Equatorius had been placed in another hominoid genus from the African middle Miocene, Kenyapithecus. There had been conflicting opinions about the relationship of Kenyapithecus to great apes and humans. Some evidence from the paleontological record showed a close relationship, even suggesting that it was an early member of this group of species with a common evolutionary ancestry. Other evidence seemed to show that there was a much more distant relationship between Kenyapithecus and living great apes and humans. "It is now clear that one of the reasons for this diversity of opinion was that the Kenyapithecus sample actually contained two genera," Kelley points out. "Specimens of one of the genera are fairly primitive and those of the other genus are more derived. The sample was giving off mixed signals."

The partial skeleton from Kipsaramon includes much of the forelimbs and shoulders, as well as portions of the vertebral column and most of the lower jaw and dentition, making it the first specimen from the middle Miocene (approximately 16,000,000 to 11,000,000 years ago) to preserve associated cranial and post-cranial remains. This enabled Kelley and his associates to compare the Kipsaramon skeleton with remains from all of the other African middle Miocene sites, especially the small Kenyapithecus sample from Ft. Ternan in Kenya, which consists almost entirely of teeth and jaw fragments.

Kenyapithecus shares some features with living great apes that the more primitive Equatorius does not. These include relatively slender, high-crowned canine teeth and robust incisors, and a restructuring of the bony anatomy of the zygomatic area of the face, which, among other things, alters the length and position of some of the chewing muscles.