New fossil primate species found in West Texas

A lemur-like creature, among the last of North American primates, once lived in tropical West Texas over 43 million years ago.

A new kind of primate, that lived 43 million years ago, has been discovered in the Big Bend region of West Texas. Named Mescalerolemur horneri, it was among the last primates endemic to North America. This petite creature, weighing just 370 grams, is related to modern-day lemurs found only in Madagascar.

Greater Dwarf Lemur (Cheirogaleus major). It was about the same size, and probably resembled Mescalerolemur horneri. Image Credit: Adam Britt via Wikimedia Commons.

The discovery was published online in May 2011, in the Journal of Human Evolution by Chris Kirk, of at University of Texas at Austin, and his collaborators.

The first Mescalerolemur fossil, a tooth, was found in 2005 by a University of Texas student at a location called Purple Bench in Big Bend. More fossils were later uncovered by Kirk and his student volunteers. At first, Kirk thought he had found a new smaller species of another known primate from that region, but as he studied more fossils, he began to realize that he was not just looking at a different species, but an entirely new genus (a collection of species with similar characteristics).

For much of the Eocene, a geological epoch spanning 56 to 34 million years ago, Earth was a warmer moister place, with much of the continents covered in forests. Tropical forests of North America were home to many warm-adapted animal species including primates.

Mescalerolemur, and another primate also found at Big Bend, Mahgarita stevensi, belong to an extinct primate group known as adaptiforms. This group occupied much of the Northern Hemisphere during the Eocene. Mescalerolemur and Mahgarita, however, were closely related to European and Asian adaptiforms rather than North American adaptiforms from earlier in the Eocene. This indicated that animal migrations from East Asia to North America were occurring during the Eocene when the Bering land bridge – now submerged under the Bering Sea – between east Siberia and Alaska, was exposed during periods of lower sea level.

Around the middle of the Eocene, the climate began to cool down, and towards the end of the epoch, much of the tropical flora and fauna in North America had become extinct due to cooler temperatures. The West Texas region was one of the last stands for tropical species in North America.

Mescalerolemur horneri‘s partial upper jaw (in two pieces, at left) and partial lower jaw (at right) (scale bar is 2 mm). Image Credit: University of Texas at Austin.

Said Kirk in a press release,

These Texas primates are unlike any other Eocene primate community that has ever been found in terms of the species that are represented. 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.

Mescalerolemur horneri‘s partial right lower jaw (scale bar is 2 mm). Image Credit: University of Texas at Austin.

Fossil remains of an animal that lived 43 million years ago have revealed a new primate species that once inhabited the ancient tropical forests of West Texas. Named Mescalerolemur horneri, this diminutive primate, weighing just 370 grams, was related to modern-day lemurs. It was not a descendant of other primates that had once lived in North America, instead, its ancestors came from Asia, crossing the exposed Bering land bridge that connected Siberia to Alaska. It was among the last of North America’s primates to go extinct during a period of global cooling towards the end of the Eocene, a geologic epoch spanning 56 to 34 million years ago.

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