Thescelosaurini were a group of small to medium-sized plant-eating dinosaurs that inhabited North America during the Late Cretaceous epoch. A newly discovered species of scelosaurine Fona herzogae shows evidence that these dinosaurs spent at least part of their time in underground burrows.
Fona herzogae. Image credit: Jorge Gonzalez.
Fona herzogae lived approximately 99 million years ago (Cretaceous period) in what is now Utah.
At the time, the area was a large floodplain ecosystem sandwiched between the shores of a mighty inland ocean to the east and active volcanoes and mountains to the west. It was a warm, humid, muddy environment with numerous rivers flowing through it.
Paleontologists from North Carolina State University and the North Carolina Museum of Natural Sciences discovered 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 distinguishing features, alerted them to the possibility of burrowing.
Fona herzogae was a small-bodied, plant-eating dinosaur about the size of a large dog with a simple body plan.
It lacks the bells and whistles that characterize its highly decorated relatives such as horned dinosaurs, armored dinosaurs, and crested dinosaurs. But that doesn’t mean Fona herzogae it was boring.
Fona herzogae it shares several anatomical features with animals known for digging or burrowing, such as large biceps muscles, strong muscle attachment points on the hips and legs, fused bones along the pelvis—probably helping with stability when digging—and hind limbs that are proportionally larger than forelimbs extremities. But this is not the only evidence that this animal spent time underground.
“The bias in the fossil record is toward larger animals, primarily because in floodplain environments like the Mussentuchit, small bones at the surface are often scattered, rotted, or picked up before burial and fossilization,” says Haviv Avrahami, Ph.D. student at NC State and digital technician for the new Dueling Dinosaurs program at the North Carolina Museum of Natural Sciences.
“But Fona herzogae is often found complete, with many bones preserved in their original postmortem position, chest down with the forelimbs extended, and in exceptionally good condition.”
“If it had been underground in a burrow before death, this type of preservation would be more likely.
Dr. Lindsay Zanno, associate research professor at NC State, head of paleontology at the North Carolina Museum of Natural Sciences and corresponding author of the paper, agrees.
“Fona herzogae skeletons are much more common in this area than we would predict for a small animal with fragile bones,” says Dr. Zanna.
“The best explanation for why we find so many of them and get them in small bundles of multiple individuals is that they lived at least part of the time underground.”
“In fact, Fona herzogae he’s done the hard work for us by burrowing all over this area.”
Although researchers have yet to identify the underground burrows Fona herzogaethe tunnels and chamber of his nearest relative, Oryctodromeus, have been found in Idaho and Montana. These findings support the idea that Fona herzogae also used burrows.
Fona herzogae is also a distant relative of another famous North Carolina fossil: Willo, a Thescelosaurus lackus a specimen currently housed in a museum is also believed to have adaptations for a semifossorial – or semi-subterranean – lifestyle.
“Thescelosaurus lackus was at the end of that line— Fona herzogae is its ancestor from about 35 million years ago,” says Avrahami.
Scientists believe Fona herzogae is key to expanding our understanding of Cretaceous ecosystems.
“Fona herzogae it gives us a glimpse into the third dimension that an animal can occupy by moving underground,” says Avrahami.
“It adds to the richness of the fossil record and expands the known diversity of small-bodied herbivores that remain poorly understood despite being an incredibly integral part of Cretaceous ecosystems.”
“People tend to have a myopic view of dinosaurs that doesn’t keep up with the science,” says Dr. Zanna.
“We now know that dinosaur diversity spans from small arboreal gliders and nocturnal hunters to grazer-like sloths and, yes, even underground denizens.”
The work appears in Anatomical record.
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Haviv M. Avrahami et al. A new semifossorial thescelosaurine dinosaur from the Cenomanian Mussentuchite Member of the Cedar Mountain Formation, Utah. Anatomical record, published online July 9, 2024; doi: 10.1002/ar.25505
This article is a version of a press release provided by North Carolina State University.