By Katrina Dix
As Caldwell Buntin, Ph.D., neared the finish line for his doctorate in ocean and earth sciences at Թϱ last year, he spent hundreds of hours scrutinizing a computer screen through 3D lenses clipped to his glasses, .
In geological terms, he hit the jackpot, finding 25 new sets of tracks and massively expanding the foundation laid by leading paleontologist Martin Lockley, Ph.D. In 2016, Dr. Lockley found two sets of scrapings from two-legged creatures called theropods and determined after ruling out other possibilities such as digging for food and water or marking their territories.
While conducting fieldwork on site with Dr. Lockley in 2021, Dr. Buntin found a third set of scrapings. Based on the numbers found at larger sites, he thought he might be able to spot a few more. Instead, shortly after Dr. Lockley died in 2023, Dr. Buntin quickly found dozens in digital images.
“It was intimidating to find these knowing I couldn’t talk to him and get his opinion,” he said. “And then just being a student, it was a little disconcerting. It was exciting, but at the same time it made me really nervous.”
Using geological survey images accurate down to a grain of sand, he searched an area about 500 meters square — around the size of a pool for swimming laps — at Dinosaur Ridge in Colorado, one of the foremost in North America.
“The main problem was that as of February 2024, the state of Colorado has a moratorium on walking on any surface that has dinosaur trackways. So now everything is all digital,” Dr. Buntin said.
He used technology called photogrammetry, which projects overlapping photos into three-dimensional space, runs them through a computer program and creates a model of the planet’s surface.
The scrapings, which Dr. Buntin said the dinosaures likely made within a three-month period eons ago, were preserved through a combination of moist earth, iron staining from a microbial mat on the surface of the ground, and individual bacterial cells that secreted a kind of glue.
“You have the combination of a bio-glue as well as the sediment being wet, and then bacteria can start to create cement while still growing,” he said. “It starts to lithify, or turn to rock, while it’s still exposed to air.”
Dr. Buntin and one of his co-authors, Tom Moklestad, Ph.D., think the theropods were building nests to show off for potential mates, and then performing a courtship dance around them. The same behavior is seen today in plovers, a wetland bird, he said.
Theropods could range in size from tiny, feathered bipeds all the way up to Tyrannosaurus rex, but the researchers believe these markings are from animals about the size of a modern-day ostrich — possibly Ornithomimus, which may have looked like an ostrich, too.
“We don’t have any direct evidence of nesting. We have really shallow scrapes, and in addition to those, we have these nearly circular bowl-shaped structures with them every time,” he said. “But we don’t have eggs, and if we do find something that resembles an egg, we can’t sample, either here or at the other sites, and we can’t walk on the surfaces to check what they are. It’s kind of a pickle.”
Similar marks have been found at three other sites, some much larger than Dinosaur Ridge. But those are on federally protected land, where researchers are only allowed occasional visits — and Dinosaur Ridge is not.
Any evidence of dinosaur mating is extremely rare, and very little is known about it, Dr. Buntin said — especially for theropods, for which only about two dozen nesting sites have been found. He thinks this was a courtship site rather than a nesting site because when a colony nests together, the nests are typically evenly spaced, he said. In courtship, where there’s competition for mates, the remnants are closely clustered.
“One of the biggest hurdles with trying to call them nests is that no rims have been described yet,” Dr. Buntin said. “Usually, with any of the nests that have been described, there’s been some kind of rim on the outside. We’re also looking for any egg material or even just traces of an egg being there, and for one of these we think we might have that.”
He plans to look at the other sites where similar scrapings have been found, and if they find similar potential egg traces there as well, it could support the argument that these were nests.
Dr. Buntin is hopeful the moratorium may be lifted in the next couple of years, allowing him to visit the trackways again and examine the evidence he’s found with his own eyes — which he said seem to be fine despite the months of 3D screen time — and not just through a computer screen.