West Texas Jurassic: new fossils are a Texas first
“Welcome to Jurassic World.”
Thanks to Hollywood, the Jurassic Period — with its dinosaurs and other charismatic reptiles — holds a special place in the popular imagination.
But the Jurassic in Texas has long been a blank. Now that's changed. Scientists recently announced the discovery in West Texas of the fossils of a vanished marine reptile called a plesiosaur. It's our first glimpse into the state's Jurassic wildlife.
It's just two weathered fragments of backbone and limb. But it's a landmark find. Steve May, of the University of Texas at Austin's Jackson School, is part of the research team.
“Most paleontologists would tell you this is kind of scrappy stuff,” May said. “It's not like we found a nice, big plesiosaur skeleton laid out with the skull and everything. But you've got to remember there's a 55-million-year interval of Earth history where we had no vertebrates before this.”
Paleontology relies on the surface exposure of fossil-bearing rocks, and Texas has a world-class fossil record. The red rocks of the caprock canyons date to the Triassic Period, more than 200 million years ago — and reveal Triassic creatures. Big Bend National Park abounds in more recent Cretaceous fossils. But rocks from the Jurassic — which lasted from about 200 to 145 million years ago —- simply aren't part of the Texas landscape.
But studying the geological archives, May located an exception — a 13-square-mile exposure of Jurassic rocks in the Malone Mountains, near Sierra Blanca, in Hudspeth County.
“And that's the entire extent of outcrop of Jurassic-age rocks in the state of Texas,” May said. “In the subsurface, there's a lot of Jurassic. But in terms of outcrop, which is how you find fossil vertebrates, there's not much.”
The team traveled to the isolated mountains in 2015 and 2016. They “prospected” on state land. But private landowners also granted access, and it was on one such property – the Jackson family ranch – that they found the plesiosaur bones.
This “short-necked” plesiosaur had a football-shaped body, flippers, a long tail and an alligator-like head. It likely preyed on fish. How big was it?
“Probably on the order of 15 to 20 feet long,” May said. “Not huge, but you'd know it if it was chasing you in that Jurassic shallow marine setting.”
That shallow ocean was the Chihuahua Trough — a narrow band of sea comparable to the Gulf of California, which joined the Pacific, and, sometimes, the Gulf of Mexico. Siltstones, sandstones and limestone were laid down here between 155 and 145 million years ago.
The exposure of these rocks — the Malone Formation — is thanks to the tectonic activity that has shaped our region's mountainous landscapes. The Malone Formation was driven up by the same compressive forces that raised the Rockies.
The team found other Jurassic fossils — including ammonites, squid-like creatures with coiled shells. They found pine cones and other plant material carried into the sea by rivers. And there's likely more to find. May said there's a chance of a “bloat and float” – an entire stegosaurus, brachiosaurus or other dinosaur that died onshore and was carried into the waters.
“I hope that there are others who kind of pick up the challenge now,” he said. “There's a lot of Malone Formation we didn't prospect. I hope some younger paleontologists, with better knees than mine, want to get out there and continue the work.”
For now, the West Texas mountains have opened a new vista into the state's deep past.