Underground life suited newly discovered dinosaur, study finds

The age of dinosaurs was not limited to the surface of the ground. A recently discovered ancestor of Thescelosaurus shows that these animals spent at least part of their time in underground burrows. This new species contributes to a better understanding of life during the Middle 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 region was a vast floodplain ecosystem wedged between the shores of a vast inland ocean to the east and active volcanoes and mountains to the west. It was a hot, humid, muddy environment with many rivers flowing through it.

Paleontologists from North Carolina State University and the North Carolina Museum of Natural Sciences discovered the fossil, along with other specimens of the same species, in the Mussentuchit Member of the Cedar Mountain Formation in 2013. The preservation of these fossils, along with some distinctive features, alerted them to the possibility of excavation.

Fona was a small, herbivorous dinosaur about the size of a large dog, with a simple body plan. It lacked the flourishes that characterized 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 to dig or burrow, such as large biceps muscles, strong muscle attachment points on the hips and legs, fused bones along the pelvis (likely to aid stability while digging), and hind limbs that are proportionally larger than the forelimbs. But that’s not the only evidence that this animal spent time underground.

“The bias in the fossil record favors larger animals, primarily because in floodplain environments like the Mussentuchit, small bones on the surface often disperse, rot, or are scavenged before burial and fossilization,” says Haviv Avrahami, a doctoral 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 paper describing the work now published in The anatomical file.

“But Fona is often found whole, with many bones preserved in the initial death position, chest down and forelimbs spread, and in an exceptional state of preservation,” Avrahami says. “If he had already been buried in a burrow before his death, this type of preservation would have been more likely.”

Lindsay Zanno, associate research professor at North Carolina State University, chair of paleontology at the North Carolina Museum of Natural Sciences and corresponding author of the book, agrees.

“Fona skeletons are much more common in this area than you might think for a small, fragile-boned animal,” Zanno says. “The best explanation for why we’re finding so many of them, and collecting them in small groups of several individuals, is that they lived at least part of the time underground. In fact, Fona did most of the work for us, burrowing all over this area.”

Although researchers have yet to identify Fona’s underground burrows, the tunnels and chambers of its closest relative, Oryctodromeus, have been discovered in Idaho and Montana. These findings support the idea that Fona also used burrows.

The genus name Fona comes from the ancestral creation story of the Chamorro people, who are the indigenous population of Guam and the Pacific Mariana Islands. Fo’na and Pontan were sibling explorers who discovered the island and became the earth and sky.

The species name honors Lisa Herzog, 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 pay homage to the indigenous mythology of Guam, where my Chamorro ancestors come from,” Avrahami explains. “In the myth, Fo’na became part of the earth when she died, and from her body a new life was born, which to me is connected to fossilization, beauty, and creation. Fona was most likely covered in a cloak of colorful feathers.”

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

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

“T. neglectus was at the end of this lineage – Fona is its ancestor from about 35 million years ago,” Avrahami says.

Researchers believe Fona is key to expanding our understanding of Cretaceous ecosystems.

“Fona gives us a glimpse into the third dimension that an animal can occupy while moving underground,” Avrahami says. “It adds to the wealth of fossils and expands the known diversity of small-bodied herbivores, which remain poorly understood despite being incredibly essential components of Cretaceous ecosystems.”

“People tend to have a myopic view of dinosaurs that hasn’t kept up with the evolution of science,” Zanno says. “We now know that dinosaur diversity ranged from tiny tree-dwelling gliders and nocturnal hunters to sloth-like grazers and even subterranean dwellings.”