Thescelosaurines were a group of small to medium-sized, plant-eating dinosaurs that inhabited North America during the Late Cretaceous period. Newly discovered thescelosaurine species 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 massive inland ocean to the east and active volcanoes and mountains to the west. It was a warm, wet, muddy environment with many rivers running through it.
Paleontologists from North Carolina State University and the North Carolina Museum of Natural Sciences discovered the fossil—and other specimens from the same species—in the Mussentuchit Member of the Cedar Mountain Formation, beginning in 2013.
The preservation of these fossils, along with several distinctive features, alerted them to the possibility of excavation.
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 shares some anatomical features with known burrowing or burrowing animals, such as large biceps muscles, strong muscle attachment points in the hips and legs, fused bones along the pelvis—which may aid in stability while burrowing—and hind limbs that are proportionally larger than the fore limbs. But this is not the only evidence that this animal spent time underground.
“The bias in the fossil record is toward larger animals, largely because in flood environments like the Mussentuchit, small bones at the surface are often dispersed, decayed, or buried 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 Science.
“But Fona Herzogae it is often found complete, with many of its bones preserved in its original death pose, chest down with the forelimbs spread out, and in remarkably good condition.
“If it had been underground in a burrow before death, it would have made this kind of preservation 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 expect for a small animal with fragile bones,” says Dr. Zanno.
“The best explanation for why we find so many of them and recover them in small herds of many individuals is that they lived at least part of the time underground.”
“Essentially, Fona Herzogae did the hard work for us, burying itself all over this area.”
Although researchers have not yet identified the underground lairs of Fona Herzogaethe tunnels and chamber of his nearest relative, Orychtodromeus, have been found in Idaho and Montana. These findings support the idea that Fona Herzogae also used dens.
Fona Herzogae is also a distant relative of another famous North Carolina fossil: Willo, a Thescelosaurus neglectus specimen currently housed in the museum and also thought to have adaptations for a semi-fossorial – or partially subterranean – lifestyle.
“Thescelosaurus neglectus was at the end of this line – Fona Herzogae it is its ancestor from about 35 million years ago,” says Avrahami.
Researchers believe Fona Herzogae is key to expanding our understanding of Cretaceous ecosystems.
“Fona Herzogae it gives us insight 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, which are poorly understood despite being incredibly integral components of Cretaceous ecosystems.”
“People tend to have a myopic view of dinosaurs that doesn’t line up with the science,” says Dr. Zanno.
“We now know that the diversity of dinosaurs ranged from small arboreal crawlers and nocturnal hunters, to sloth-like grazers and yes, even underground denizens.”
The work appears in Anatomical Registration.
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Haviv M. Avrahami et al. A new semi-fossorial thescelosaurine dinosaur from the Cenomanian-aged Mussentuchit Member of the Cedar Mountain Formation, Utah. Anatomical Registration, 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.