NATURE NOTES:
Ancient Primates of the Big Bend

By Andrew Stuart

Naturalists know that the Big Bend’s harsh conditions mask a tremendous diversity of living things. The Chihuahuan Desert is home to plants and animals found nowhere else on earth.

But did you know it was once home to an assortment of distinctive, endemic primates? Today, excavations are shedding light on this surprising part of West Texas history.

As primates ourselves, we can’t help but take a special interest in the history of these mammals. It’s a story that stretches back 65 million years.

Scientists say primates emerged in Southeast Asia in the early Paleocene Epoch, just after the disappearance of the dinosaurs.

For ages, they were limited to the Asian jungles. But about 56 million years ago, the planet warmed significantly. At this time – the beginning of the Eocene Epoch – the Arctic Ocean would have been warm enough for a summer swim.

In these balmy conditions, forests spread across the globe. And so did forest creatures – including primates.

As early as the 1880s, scientists were finding primate fossils in Wyoming. Many were “notharctids” – extinct primates related to modern-day lemurs and lorises. But the planet cooled as the Eocene progressed, and primates vanished from the Northern Rockies by the late Eocene.

But in West Texas, it was a different story.

Chris Kirk is a paleontologist at the University of Texas at Austin. In a decade of excavations, he’s discovered many new primates in the Big Bend.

It’s almost an embarrassment of riches – the number of taxa that are previously unknown to science that have come out of those West Texas sediments,” Kirk said. “It’s eight hours from my home in Austin, and you can go and sit down on day one and pick up a new genus of primate. There are not that many places where you can go and do that in this day and age.”

The center of Kirk’s study has been the Dalquest Desert Research Station, straddling the Brewster-and-Presidio County line south of Marfa. The 3,000-acre property is owned by Midwestern State University, in Wichita Falls.

In a canyon called the Devil’s Graveyard, Kirk and his colleagues and students have recovered the teeth, jaw bones and bits of crania of ancient primates.

What were these creatures?

In the daytime, Kirk said, the forests of Eocene West Texas were alive with the sound of primates called adapoids. They weighed up to 12 pounds. A second group – the omomyoids – were nocturnal.

Adapoids tend to be the larger, day-active fruit- and leaf-eating primates,” Kirk said, “and omomyoids tend to be these smaller, nocturnal, insect-, gum- and fruit-eating primates. You can imagine things like living tarsiers or bush babies for omomyoids, and things like living ruffed lemurs or ring-tailed lemurs for the adapoids.”

Kirk named one of his finds “Mescalerolemur horneri.” The ancestor of this adapoid migrated across the Bering Land Bridge – and made its home in West Texas. It established its own evolutionary line. A descendant, named Mahgarita stevensi, continued to live here into the late Eocene – 38 million years ago. Kirk has also discovered new omomyoid primates.

 

So it appears that what we’re sampling is an entire primate fauna – a community of primates – that is sufficiently distinct from other fossil localities where you find primates of similar age in North America,” he said. “There is very little resemblance between the primates that you find in the Devil’s Graveyard and primates that you find in other places.”

Why was there such a unique community of primates here? Scientists don’t know for sure. But as the planet grew drier, West Texas may have been an isolated outpost of tropical forests.

By the close of the Eocene, the forests were replaced by savannah. The West Texas primates disappeared – leaving no descendants.

But today, the fossils of the Big Bend are adding to the story of primate development. Kirk said that, as a native Texan, that’s a source of pride.

One of the things I like most about my job is the ability to inform my fellow Texans – ‘Hey, we’ve got this amazing, rich fossil record that’s part of our natural history and part of heritage here in Texas,’” Kirk said. “The fact that most Texans don’t know this story is part of what makes it compelling to me.”

It’s another example of West Texas’ rich natural history.