Ancient primates took refuge in Big Bend
By MEGAN WILDE / The Big Bend Gazette (November 2008)
Around 44 million years ago, when North American primates were perishing as the climate cooled and dried, a unique group of primates found refuge and proliferated amid the tropical forests and heaving volcanoes that blanketed far West Texas.
That’s the latest chapter in primate history revealed by new fossil evidence found in south Brewster County. Chris Kirk, a University of Texas at Austin physical anthropologist, uncovered chunks of jaw bone and two molars embedded in the pastel-banded canyons of the Devil’s Graveyard Formation northwest of Big Bend National Park. Kirk and Duke University anthropologist Blythe Williams recently determined the 44- to 43-million-year-old remains belonged to a new genus and species of primate, Diablomomys dalquesti, that they believe lived only in the Big Bend region. Their findings were published recently in the Journal of Human Evolution.
According to the anthropologists, Diablomomys was quite small, subsisting on a diet of insects and fruit as it roamed the night-time tropical forest. These creatures were members of one of two North American primate groups, called the omomyoids, which probably occupied a dead-end branch on their evolutionary family tree. Williams said the omomyoids’ closest living relatives may be tiny bug-eyed tarsiers, monkeys, apes and humans.
Diablomomys was not the only prehistoric primate resident of Big Bend, Kirk explained. So far, fossil evidence of at least three other primate species has been unearthed here, including the crushed skulls of another genus unique to the Devil’s Graveyard. That genus, Mahgarita, belonged to the other North American primate group, the adapoids, which Williams said are relatives of modern-day lemurs and lorises. And so, living in the Trans-Pecos were four representatives of both omomyoid and adapoid primates, and at least two of those species have been found nowhere else on the continent.
“That suggests this part of West Texas was an interesting place back then,” Kirk said.
What’s most interesting, he and Williams said, is that diverse community thrived here during an era researchers previously thought primates were vanishing from North America. The primate fossils Kirk and other researchers have found in the Big Bend region date from around 44 or 43 million years ago, the dramatic finale of the Eocene epoch.
The Eocene was the warmest period in Earth’s relatively recent history, lasting from about 55 to 34 million years ago, Kirk explained. Primates flourished in the tropical forests that covered North America during the early Eocene millennia, and Kirk said thousands of primate fossils have been found across the continent from that period.
But the primate party ended when the Eocene drew to a close. Antarctica split off from South America, and a vast, super-cold ocean current began to form around the polar continent, Kirk explained. That created a planetary air conditioner that caused the single biggest drop in global temperature ever. As North America chilled and dried, the tropics retracted southward.
“Where you had seen primates and other tropically adapted species in the north – boom! suddenly they’re gone,” Kirk said. “At the same time, you actually see a blossoming of primates in some lower latitude areas.”
A trove of fossil evidence yielded in West Texas has shown that this region in particular remained humid and warm into the late Eocene, making it an island-like refuge of choice primate habitat, Kirk explained. Here volcanoes puckered and pleated the earth’s crust – creating many of the mountain ranges we recognize today – and huge palm-lined rivers wound sluggishly through lowland rainforests. In that environment, Diablomomys and Mahgarita appeared on the evolutionary scene and joined other primates who had followed the shrinking tropics to far West Texas.
“Elsewhere at this time primates are declining in numbers and diversity, but it’s nice enough still in West Texas that they’re not only surviving, they’re diversifying,” Kirk said. “That’s what’s so cool.”
More information on Kirk’s work at the Dalquest Research Site is at https://webspace.utexas.edu/kirkec/www/dalquest.html. Kirk said he’s always looking for new field sites and welcomes anyone curious about fossils on their property to contact him.