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Study of Ancient Primate Counters "Darwinus" Discovery

A scientific analysis of a recently discovered adapiform, an ancient primate, reveals that the fossil, called Afradapis, is not on the evolutionary lineage of anthropoids (Old World Monkeys and higher primates, including humans) but instead more closely to lemurs and lorises.

Led by Stony Brook University paleontologist Erik R. Seiffert, Ph.D., the research supports the more commonly held theory on adapiform evolution and refutes a claim earlier in 2009 by scientists that described another adapiform, called Darwinius, as a direct link to the lineage leading to higher primates. The study findings are reported in the October 22 issue of Nature.

The study of Afradapis, recently discovered in northern Egypt, involves a complete analysis of the jaw and teeth that reconstructs the most likely evolutionary tree of the 37 million year-old fossil. Dr. Seiffert and colleagues used a scientific method called parsimony evidence that compares Afradapis’ jaw and teeth across 117 living and extinct primates.

“Our analysis is the first to incorporate evidence from all the key players in the anthropoid origins debate, that is all of the fossil species that have been proposed as possible early anthropoids, including a large sampling of adapiform primates,” says Dr. Seiffert, Assistant Professor in the Department of Anatomical Sciences, Stony Brook University. “The adapiform lineage that includes Darwinius and Afradapis has been particularly controversial, and we are finding new evidence that allows us to be increasingly confident that the anatomical features that these adapiforms share with anthropoids are due to convergent evolution and not common ancestry.”

The controversy on the adapiform evolutionary line escalated when a team of European and American paleontologists reported in the May 19, 2009, online edition of PloS One that their two-year analysis of Darwinius indicates the adapiform is the first link to all humans, supporting a common ancestry theory. Some media publicized their finding that the “missing link” to anthropoids had been found.

Conversely, Dr. Seiffert and colleagues’ analysis of Afradapis, and thus ancient adapiforms, supports the convergence evolutionary theory and contributes to a growing body of evidence that indicates that convergent evolution was a common phenomenon in early primate evolution. Convergent evolution is a process in which organisms and animals become similar in shape or structure, in response to similar environmental conditions, despite that their evolutionary lineage is different.

Dr. Seiffert explains that the common ancestry theory of adapiforms linking them more closely to higher primates than lemurs hinges on features such as fusion of the two halves of the jaw, reduction and loss of the first frew premolar teeth, and the presence of front teeth (incisors) that are shaped like a spatula. However, he points out that the study of Afradapis shows the fusion of the two halves of the jaw clearly evolved convergently in adapiforms and anthropoids, as even the earliest anthropoids have unfused mandibles.

“Incisor teeth that are shaped like a spatula might have been present in the last common ancestor or all primates, and so would not specifically support a link between adapiforms and anthropoids,” adds Dr. Seiffert. “Our analysis also indicates that the reduction and/or loss of the first few premolars must have evolved convergently in adapiforms and anthropoids because of some of Afradapis’ close relatives retain a full complement of four premolars on each side of the jaw, as in many other early mammalian relatives of primates.”

In the anatomical analysis published in Nature titled “Convergent evolution of anthropoid-like adaptations in Eocene adapiform primates,” the authors point out that at the very least Afradapis, the largest non-anthropoid primate ever documented in Afro-Arabia, provides surprising new evidence for primitive primate diversity in the Eocene era of Africa. They also contend that their findings raise the possibility that ecological competition between adapiforms and higher primates, based on environmental and geography changes, led to anatomical adaptations by both and played an important roles during early primate evolution.

The research for the study was supported by the Research Foundation of the State University of New York, and grants from the U.S. National Science Foundation and The Leakey Foundation.

In addition to Dr. Seiffert, co-authors of the study include: Jonathan M. G. Perry, Department of Anatomy, Midwestern University; Elwyn L. Simons, Division of Fossil Primates, Duke Lemur Center, Duke University; and Doug M. Boyer, Department of Ecology & Evolution, Stony Brook University.

The Department of Anatomical Sciences is one of 25 departments within Stony Brook University School of Medicine. The department includes graduate and doctoral programs in Anatomical Sciences. Fields of study include research on human evolutionary anatomy, morphology and vertebrate paleontology. Many faculty members in the department are also participants in an interdepartmental graduate program in anthropological sciences that is recognized worldwide for its faculty and research strengths in functional morphology and human evolution.

Greg Filiano | Newswise Science News
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