Research shows life underground suited newly discovered dinosaur

The age of the dinosaurs was not only explored above ground. A recently discovered ancestor of Thescelosaurus shows that these animals spent at least part of their time in underground burrows. The new species contributes to a more complete understanding of life during the mid-Cretaceous, both above and below ground.

The new dinosaur, Fona [/Foat’NAH/] herzogae lived 99 million years ago in what is now Utah. At that time, the area was a large 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 several distinguishing features, alerted them to the possibility of burials.

Fona was a small, herbivorous dinosaur about the size of a large dog with a simple body plan. 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 was boring.

Fona 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 provide stability while digging), and hind limbs that are proportionally larger than its forelimbs. But that’s not the only evidence that this animal spent time underground.

“The fossils in the record are biased toward larger animals, especially because in floodplains like the Mussentuchit, small bones often get scattered on the surface, rotted away, or eaten before being buried and fossilized,” said Haviv Avrahami, a doctoral candidate at NC State and a digital technician for the North Carolina Museum of Natural Sciences’ new Dueling Dinosaurs Program.

Avrahami is the first author of the paper describing the work now published in The anatomical report.

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

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 skeletons are much more common in this area than we would expect for a small animal with fragile bones,” Zanno says. “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 were living underground at least some of the time. In effect, Fona did the hard work for us by burying itself all over this area.”

Although researchers have not yet identified Fona’s underground burrows, the tunnels and chamber of its close relative, Oryctodromeus, have been found in Idaho and Montana. These finds support the idea that Fona also used burrows.

The generic name Fona comes from the ancestral creation story of the Chamorro people, the indigenous people of Guam and the Pacific Mariana Islands. Fo’na and Pontan were brother and sister explorers who discovered the island and became the land and the sky.

The species name honors Lisa Herzog, the paleontology operations manager at the North Carolina Museum of Natural Sciences, for her invaluable contributions and dedication to the field of paleontology.

“I wanted to honor the indigenous mythology of Guam, where my Chamorro ancestors come from,” Avrahami says. “In the myth, Fo’na became part of the land when she died, and from her body new life emerged, which for me has to do with fossilization, beauty, and creation. Fona was most likely covered in a downy layer of colorful feathers.

“The species name is from Lisa Herzog, who was instrumental in all this work and discovered one of the most exceptional Fona specimens, consisting of several specimens preserved together in what was probably a burrow.”

Fona is also a distant relative of another famous North Carolina fossil: Willo, a specimen of Thescelosaurus neglectus currently housed at the museum that is also thought to have adaptations for a semi-fossil — or partially subterranean — lifestyle, research published in late 2023 by Zanno and former NC State postdoctoral researcher David Button.

“T. neglectus was at the end of this line; Fona is its ancestor, about 35 million years earlier,” Avrahami says.

The researchers are convinced that Fona is crucial for increasing our knowledge of Cretaceous ecosystems.

“Fona gives us insight into the third dimension that an animal can inhabit by moving underground,” Avrahami says. “It adds to the richness of the fossil record and expands the known diversity of small herbivores, which are still poorly understood despite being incredibly integral components of Cretaceous ecosystems.”

“People often have a narrow view of dinosaurs that hasn’t been caught up with by science,” Zanno says. “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.”