Living underground suited a newly discovered dinosaur, study finds

The Age of Dinosaurs was not only conducted above ground. A newly discovered ancestor of Thescelosaurus shows that these animals spent at least part of their time in underground burrows. The new species contributes to a fuller understanding of life during the Middle Cretaceous—both above and below ground.

A new dinosaur, Fona [/Foat’NAH/] herzogae lived 99 million years ago 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 distinctive features, alerted them to the possibility of burrowing.

Fona was a small-bodied, herbivorous 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 was boring.

Fona shares several anatomical features with animals known for digging or burrowing, such as large biceps muscles, strong muscle points on the flanks 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.

Avrahami is the first author of the article describing the work now published in Anatomical record.

“But Fona is often found complete, with many bones preserved in the original death pose, chest down with forelimbs extended, and in exceptionally good condition,” says Avrahami. “If it was underground in a burrow before it died, it would be more likely.

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 skeletons are much more common in this area than we would predict for a small animal with fragile bones,” Zanno says. “The best explanation for finding so many of them and getting them in small bundles of a few individuals is that they lived at least part of the time underground. The Fona basically did the hard work for us by burying them all.” over this area.”

Although scientists have not yet identified the underground burrows of Fona, the tunnels and chamber of its closest relative, Oryctodromea, have been found in Idaho and Montana. These findings support the idea that the Fona also used burrows.

The family name Fona comes from the creation story of the ancestors of the Chamorro people, who are the original inhabitants of Guam and the Pacific Mariana Islands. Fo’na and Pontan were brother and sister explorers who discovered the island and became earth and sky.

The species name honors Lisa Herzog, Manager of Paleontology Operations 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 came from,” says Avrahami. “In the myth, Fo’na became part of the earth when she died, and new life sprang from her body, which for me is associated with fossilization, beauty, and creation. Fona was most likely covered in a downy colored mantle.” feather.

“The species name is for Lisa Herzog, who was an integral part of this work and discovered one of the most exceptional specimens of Fona from several individuals preserved together in what is likely a burrow.”

Fona is also a distant relative of another famous fossil in North Carolina: Willo, a specimen of Thescelosaurus prohibitus that is currently housed in a museum and is also believed to have adaptations for a semifossorial—or semisubterranean—lifestyle, research that in late 2023 published by Zanno and former NC State postdoctoral researcher David Button.

“T. lackus was at the end of that line – Fona is its ancestor from about 35 million years ago,” says Avrahami.

Scientists believe Fona holds the key to expanding our understanding of Cretaceous ecosystems.

“Fona 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,” Zanno says. “We now know that dinosaur diversity spans from small arboreal gliders and nocturnal hunters to grazer-like sloths and, yes, even underground denizens.”