99 million-year-old fossil reveals new dinosaur species that lived in burrows

Millions of years ago, dinosaurs ruled the Earth. But not all were above-ground giants; some were small and liked to spend their time in underground burrows.

Paleontologists from North Carolina State University and the North Carolina Museum of Natural Sciences unearthed a new dinosaur species from the Cedar Mountain Formation in Utah.

This new species, called Fona herzogae , existed 99 million years ago in Utah. Along with this fossil, scientists discovered several more remains of different individuals belonging to the same species in the region.

“ Fona skeletons are way more common in this area than we would predict for a small animal with fragile bones,” said Lindsay Zanno, head of paleontology at the North Carolina Museum of Natural Sciences.

Zanno added: “The best explanation for why we find so many of them, and recover them in small bundles of multiple individuals, is that they were living at least part of the time underground. Essentially, Fona did the hard work for us, by burying itself all over this area.”

Dog-sized herbivore

The well-preserved fossil along with anatomical features suggests that these dinosaurs likely spent part of their lives in underground burrows. This form of partially subterranean living is referred to as semifossorial.

The species is the ancestor of Thescelosaurus , a genus of goat-sized dinosaurs that emerged around the end of the Late Cretaceous era in North America.

Fona’s fossilized remains point towards a burrowing lifestyle. Powerful bicep muscles, robust muscle attachment points on the hips and legs, a fused pelvis for stability while digging, and hindlimbs considerably larger than the forelimbs – all suggest Fona was well-equipped for life beneath the surface.

The examination of the specimen suggests that Fona was a large dog-sized herbivore, simpler in appearance than its flashy horned and armored cousins.

This newly described species is a distant cousin of another dinosaur that lived partially underground. Named Willo (Thescelosaurus neglectus), this dinosaur was also unearthed by North Carolina researchers.

Well-preserved remains

Unlike larger dinosaurs whose bones are more likely to fossilize, Fona’s complete skeletons suggest they died and were buried underground, possibly in their burrows.

“The bias in the fossil record is toward bigger animals, primarily because in floodplain environments like the Mussentuchit, small bones on the surface will often scatter, rot away, or become scavenged before burial and fossilization,” explained Haviv Avrahami, a Ph.D. student at NC State.

“But Fona is often found complete, with many of its bones preserved in the original death pose, chest down with splayed forelimbs, and in exceptionally good condition,” Avrahami said. “If it had already been underground in a burrow before death, it would have made this type of preservation more likely.”

Though paleontologists haven’t pinpointed its burrows yet. They have identified tunnels and chambers of its close relative, Oryctodromeus, in Idaho and Montana. This strengthens the case for Fona’s burrowing behavior.

The discovery sheds light on a hidden aspect of life during the mid-Cretaceous period, providing a more complete picture of both the above-ground and subterranean animals.

“It [Fona] adds to the richness of the fossil record and expands the known diversity of small-bodied herbivores, which remain poorly understood despite being incredibly integral components of Cretaceous ecosystems,” concluded Avrahami in the press release.

The findings have been published in the journal The Anatomical Record .