New primate fossil found in Texas

U. TEXAS-AUSTIN (US) — A prehistoric primate that lived in the badlands of west Texas about 43 million years ago was more bush baby than human.

The previously unknown species, Mescalerolemur horneri, weighed only about 370 grams and would have most closely resembled a small present-day lemur. Mescalerolemur is a member of an extinct primate group—the adapiforms—that were found throughout the Northern Hemisphere in the Eocene.

Just like Mahgarita stevensi, a younger fossil primate found in 1973 in the same area called the Devil’s Graveyard, Mescalerolemur is more closely related to Eurasian and African adapiforms than those from North America.

“These Texas primates are unlike any other Eocene primate community that has ever been found in terms of the species that are represented,” says Chris Kirk, associate professor of anthropology at the University of Texas at Austin.

“The presence of both Mescalerolemur and Mahgarita, which are only found in the Big Bend region of Texas, comes after the more common adapiforms from the Eocene of North America had already become extinct. This is significant because it provides further evidence of faunal interchange between North America and East Asia during the Middle Eocene.”

By the end of the Eocene, primates and other tropically adapted species had all but disappeared from North America due to climatic cooling, so Kirk is sampling the last burst of diversity in North American primates. With its lower latitudes and more equable climate, West Texas offered warm-adapted species a greater chance of survival after the cooling began.

The research is reported in the Journal of Human Evolution.

The first isolated tooth of Mescalerolemur was found in 2005. Since then, many more primate fossils have been recovered at a locality called Purple Bench, a site that is three to four million years older than the Devil’s Graveyard sediments that had previously produced Mahgarita stevensi.

“I initially thought that we had found a new, smaller species of Mahgarita,” Kirk says.

However, as more specimens were prepared at the Texas Memorial Museum, it was determined that it was not just a new species but a new genus previously unknown to science.

Mescalerolemur’s dental anatomy reveals a close evolutionary relationship with adapiform primates from Eurasia and Africa, including Darwinius masillae, a German fossil primate previously claimed to be a human ancestor.

However, the discovery of Mescalerolemur provides further evidence that adapiform primates like Darwinius are more closely related to living lemurs and bush babies than they are to humans.

For example, the right and left halves of Mescalerolemur’s lower jaws were two separate bones with a joint along the midline, a common trait for lemurs and bush babies. Mahgarita stevensi, the closest fossil relative of Mescalerolemur, had a completely fused jaw joint like that of humans.

“Because Mescalerolemur and Mahgarita are close relatives, fusion of the lower jaws in Mahgarita must have occurred independently from that observed in humans and their relatives, the monkeys and apes,” Kirk says.

Researchers from Duke University contributed to the study.

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