Several massive, three-toed footprints etched in limestone were discovered near Big Sandy Creek during cleanup after the July 5 flood. Some of the dinosaur tracks were hidden by brush; others had been covered in sediment that was scoured away by floodwaters.
"It's one of those sort of bittersweet things about our job, is that it's the cataclysmic events that often preserve fossils in the first place and then also are exposing them," Matthew Brown, a paleontologist at UT Austin, said.
The footprints were created some 115 million years ago, Brown said, when what is now a neighborhood in Northwest Travis County was a beach on the Western Interior Seaway.
The tracks were likely made by an Acrocanthosaurus, the largest carnivore in North America during the Early Cretaceous period. They had slender bodies that stretched about 35 feet, small arms and sharp, serrated teeth to sink into prey. Several large round imprints that Brown believes are from a Paluxysaurus, a giant long-necked herbivore, were also found.
Acrocanthosaurus haven't gotten the pop-culture moment that, say, a T-Rex has. There are differences between the two, but Brown said they are mostly comparable.
"If they were chasing any one of us you wouldn't be able to tell the difference," he said.
Dinosaur tracks aren't uncommon in Central Texas. Brown said the footprints are most likely related to a known dinosaur trackway in Leander. Historically, they've been revealed by extreme weather events — a major drought in the summer of 2022 unveiled a set of Acrocanthosaurus tracks an hour away from Fort Worth.
Brown said the footprints offer insight into the animals' behavior. Several parallel sets of tracks were found in Big Sandy Creek, meaning either multiple dinosaurs were traveling together or one dinosaur was pacing. Paleontologists can study the spacing of the footprints to glean if the Acrocanthosaurus was chasing the Paluxysaurus.
Some of the tracks were previously identified by paleontologists in the '80s. Others have never been seen before. Brown said UT paleontologists plan to return to the site and use new technology — like drones and laser-surface scanning — to see what information they can uncover.
"We are used to new discoveries overturning our long-held ideas on a semiregular basis," Brown said. "And that's part of the exciting thing for us, is finding new stuff and having to reframe our perspective."
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