Thescelosaurines were a group of small to medium-sized, plant-eating dinosaurs that inhabited North America during the Late Cretaceous epoch. The 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 that 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 numerous rivers running through it.
Paleontologists from North Carolina State University and the North Carolina Museum of Natural Sciences unearthed 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 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 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, such as large bicep muscles, strong muscle attachment points on the hips and legs, fused bones along the pelvis — likely to help with stability while digging — and hindlimbs that are proportionally larger than the forelimbs. But that isn’t the only evidence that this animal spent time underground.
“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,” 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 of its bones preserved in the original death pose, chest down with splayed forelimbs, and in exceptionally good condition.”
“If it had already been underground in a burrow before death, it would have made this type 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 work, agrees.
“Fona herzogae skeletons are way more common in this area than we would predict for a small animal with fragile bones,” Dr. Zanno says.
“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 herzogae did the hard work for us, by burying itself all over this area.”
Although the researchers have yet to identify the subterranean burrows of Fona herzogae, the tunnels and chamber of its closest relative, Oryctodromeus, have been found in Idaho and Montana. These finds 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 neglectus specimen currently housed at the museum and also thought to have adaptations for a semi-fossorial — or partially underground – lifestyle.
“Thescelosaurus neglectus was at the tail end of this lineage — Fona herzogae is its ancestor from about 35 million years prior,” Avrahami says.
The researchers believe Fona herzogae is key to expanding our understanding of Cretaceous ecosystems.
“Fona herzogae gives us insight into the third dimension 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 remain poorly understood despite being incredibly integral components of Cretaceous ecosystems.”
“People tend to have a myopic view of dinosaurs that hasn’t kept up with the science,” Dr. Zanno says.
“We now know that dinosaur diversity ran the gamut from tiny arboreal gliders and nocturnal hunters, to sloth-like grazers, and yes, even subterranean shelterers.”
The work appears in The Anatomical Record.
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Haviv M. Avrahami et al. A new semi-fossorial thescelosaurine dinosaur from the Cenomanian-age Mussentuchit Member of the Cedar Mountain Formation, Utah. The 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.
Source : Breaking Science News