The age of the dinosaurs did not only take place above ground. A newly discovered ancestor of Thescelosaurus shows evidence that these animals spent at least some of their time in underground burrows. The new species contributes to a better understanding of life during the mid-Cretaceous period, both above and below ground.
The new dinosaur, Fona [/Foat’NAH/] herzogae lived 99 million years ago in what is now Utah. At the time, the area consisted of 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 unearthed the fossil – and other specimens of the same species – starting in 2013 in the Mussentuchit Member of the Cedar Mountain Formation. The preservation of these fossils, along with some distinguishing features, alerted them to the possibility of digging.
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 typical of its highly decorated relatives, such as horned dinosaurs, armored dinosaurs and crested dinosaurs. But that does not mean Fona was boring.
Fona shares several anatomical features with animals known for digging or digging, such as large biceps muscles, strong muscle attachment points on the hips and legs, fused bones along the pelvis – likely aiding stability while digging – and hind legs that are proportionally larger then the front legs. But that’s not the only evidence that this animal spent time underground.
“The bias in the fossil record is toward larger animals, especially because in floodplains like the Mussentuchit, small bones at the surface will often scatter, rot, or be swept away before being buried and fossilized,” says Haviv Avrahami, Ph.D. student at NC State and digital technician for the North Carolina Museum of Natural Sciences’ new Dueling Dinosaurs program. Avrahami is the first author of the article describing the work.
“But Fona is often found complete, with many of the bones preserved in the original death position, with the chest down and the forelimbs spread, and in exceptionally good condition,” says Avrahami. “If it had been underground in a burrow before death, this kind of preservation would be more likely.”
Lindsay Zanno, associate professor of research at NC State, chief of paleontology at the North Carolina Museum of Natural Sciences and corresponding author of the work, agrees.
“Fona skeletons are much more common in this area than we would predict for a small animal with fragile bones,” says Zanno. “The best explanation for why we find so many and find them in small groups of several individuals is that they lived at least part of the time underground. Essentially, Fona did the hard work for us by burying herself all over this area.”
Although researchers have yet to identify the underground lairs Fonathe tunnels and the chamber of his nearest relative, Oryctodromous, have been found in Idaho and Montana. These findings support the idea that Fona also used caves.
The genus 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 sky. The species name honors Lisa Herzog, paleontology operations manager at the North Carolina Museum of Natural Sciences, for her valuable contributions and dedication to the field of paleontology.
“I wanted to honor the native mythology of Guam, where my Chamorro ancestors come from,” says Avrahami. ‘In the myth, Fo’na became part of the land when she died, and from her body came new life, which for me is connected to fossils, beauty and creation. Fona was most likely covered in a fluffy coat of colorful feathers. The species name is for Lisa Herzog, who has been an integral part of all this work and discovered one of the most exceptional Fona specimens from different individuals preserved together in what was probably a burrow.”
Fona is also a distant relative of another famous fossil from North Carolina: Willo, a Thescelosaurus negusus specimen currently housed in the museum and also believed 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. neglect stood at the end of this line — Fona is its ancestor from about 35 million years ago,” says Avrahami.
The researchers believe Fona is key to advancing our understanding of Cretaceous ecosystems.
“Fona 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 still are poorly understood despite being incredibly integral components of Cretaceous ecosystems.”
“People tend to have a myopic view of dinosaurs that science has not caught up,” Zanno says. “We now know that dinosaur diversity ranged from small tree gliders and nocturnal hunters to sloth-like grazers, and yes, even underground shelters.”
The work appears in The Anatomical Record. Peter Makovicky from the University of Minnesota and Ryan Tucker from Stellenbosch University also contributed to the work.
