Thescelosaurines were a group of small to medium-sized, herbivorous dinosaurs that inhabited North America during the Late Cretaceous. The recently discovered thescelosaurine species Fona Herzogae shows that these dinosaurs spent at least part of their time in underground burrows.
Fona HerzogaePhoto: Jorge Gonzalez.
Fona Herzogae lived about 99 million years ago (Cretaceous Period) in the area that is now Utah.
At that time, the area was a vast floodplain ecosystem sandwiched between the shores of a vast inland ocean to the east and active volcanoes and mountains to the west. It was a warm, wet, muddy environment with numerous rivers flowing through it.
Paleontologists from North Carolina State University and the North Carolina Museum of Natural Sciences excavated the fossil — and other specimens of the same species — in the Mussentuchit Member of the Cedar Mountain Formation, beginning in 2013.
The preservation of these fossils, along with some characteristic features, alerted them to the possibility that they might be digging.
Fona Herzogae was a small, herbivorous dinosaur, about the size of a large dog, with a simple body.
It lacks the bells and whistles typical of its highly ornamented relatives, such as horned dinosaurs, armored dinosaurs, and crested dinosaurs. But that doesn’t mean Fona Herzogae was boring.
Fona Herzogae shares several anatomical features with animals known for digging or burrowing, including large biceps muscles, strong muscle attachments on the hips and legs, fused bones along the pelvis — likely to aid in stability while digging — and hind limbs that are proportionately larger than its forelimbs. But that’s not the only evidence that this animal spent time underground.
“The fossil record favors larger animals, largely because in floodplains like the Mussentuchit, small bones often get scattered on the surface, rotted away, or eaten before being buried and fossilized,” says Haviv Avrahami, a PhD student at NC State and a digital technician for the North Carolina Museum of Natural Sciences’ new Dueling Dinosaurs Program.
“But Fona Herzogae is often found complete, with many of the bones preserved in the original death pose, chest down and forelimbs spread, and in exceptionally good condition.”
“If the animal had already been in a burrow underground before its death, this type of preservation would have been more likely.”
Dr. Lindsay Zanno, an associate professor at NC State, chief of paleontology at the North Carolina Museum of Natural Sciences, and corresponding author on the work, agrees.
“Fona Herzogae “Skeletons are much more common in this area than we would expect for a small animal with fragile bones,” says Dr. Zanno.
“The best explanation for why we find so many of them and why we find them in small bundles of multiple individuals is that they lived underground at least part of the time.”
“Actually, Fona Herzogae has done the heavy lifting for us by burying itself all over this area.”
Although researchers have discovered the underground caves of Fona Herzogaethe tunnels and the room of his closest relative, Oryctodromeushave been found in Idaho and Montana. These finds support the idea that Fona Herzogae also used caves.
Fona Herzogae is also a distant relative of another famous fossil from North Carolina: Willo, a Thescelosaurus neglected specimen currently in the museum and also thought to have adaptations for a semi-fossil – or partially subterranean – lifestyle.
“Thescelosaurus neglected stood at the end of this line — Fona Herzogae is its ancestor from about 35 million years earlier,” says Avrahami.
The researchers believe Fona Herzogae is essential for increasing our understanding of Cretaceous ecosystems.
“Fona Herzogae “It gives us insight into the third dimension that an animal can inhabit by moving underground,” says Avrahami.
“It adds to the richness of the fossil record and expands the known diversity of small herbivores, which remain poorly understood despite being incredibly integral components of Cretaceous ecosystems.”
“People often have a myopic view of dinosaurs that is not aligned with science,” says Dr. Zanno.
“We now know that dinosaurs ranged in diversity from small tree-dwelling gliders and nocturnal hunters to sloth-like grazers and, yes, even underground shelters.”
The work appears in The anatomical report.
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Haviv M. Avrahami and allA new semi-fossil thescelosaurine dinosaur from the Cenomanian Mussentuchit Member of the Cedar Mountain Formation, Utah. The anatomical reportpublished online July 9, 2024; doi: 10.1002/ar.25505
This article is a version of a press release from North Carolina State University.