During the age of dinosaurs, these creatures were not limited to life above ground. A recently discovered ancestor of Thescelosaurus provides evidence that these animals spent at least some of their time in underground burrows. This new species offers valuable insight into life during the mid-Cretaceous period, shedding light on activities both above and below ground.
The newly identified dinosaur, Fona herzogae, inhabited what is now Utah approximately 99 million years ago. At that time, the area was a vast floodplain ecosystem situated between the shores of a massive inland ocean to the east and active volcanoes and mountains to the west. It was characterized by 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 discovered the fossil, along with other specimens of the same species, in the Mussentuchit Member of the Cedar Mountain Formation, beginning in 2013. The preservation of these fossils, combined with distinct characteristics, raised the possibility that these dinosaurs were capable of burrowing.
Fona, a diminutive herbivorous dinosaur comparable in size to a big canine, possessed a straightforward body structure, lacking the elaborate adornments seen in its horned, armored, and crested relatives. This, however, did not diminish Fona’s appeal.
Several of Fona’s physical characteristics resemble those of creatures known for burrowing or digging, including well-developed bicep muscles, robust muscle attachment points on the hips and legs, fused pelvic bones likely aiding in stability during digging, and hindlimbs that are proportionally larger than the forelimbs. These features strongly suggest that this animal had a subterranean lifestyle.
“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, a 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 paper describing the work.
“But Fona 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,” Avrahami says. “If it had already been underground in a burrow before death, it would have made this type of preservation more likely.”
“Fona skeletons are way more common in this area than we would predict for a small animal with fragile bones,” 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 did the hard work for us by burying itself all over this area.”
Researchers have not yet located the underground burrows of Fona, but the discovery of tunnels and chambers belonging to its closest relative, Oryctodromeus, in Idaho and Montana, strongly suggests that Fona also utilized burrows. The genus name Fona originates from the ancestral creation story of the Chamorro people, the indigenous inhabitants of Guam and the Pacific Mariana Islands.
According to the story, Fo’na and Pontan were sibling explorers who discovered the island and transformed it into the land and sky. Additionally, the species name pays tribute to Lisa Herzog, the paleontology operations manager at the North Carolina Museum of Natural Sciences, in recognition of her invaluable contributions and commitment to the field of paleontology.
“I wanted to honor the indigenous mythology of Guam, which is where my Chamorro ancestors are from,” Avrahami says. “In the myth, Fo’na became part of the land when she died, and from her body sprung forth new life, which, to me, ties into fossilization, beauty, and creation. Fona was most likely covered in a downy coat of colorful feathers. The species name is for Lisa Herzog, who has been integral to all this work and discovered one of the most exceptional Fona specimens of several individuals preserved together in what was likely a burrow.”
Fona is also a distant relative of another famous North Carolina fossil: Willo, a Thescelosaurus neglectus specimen that is believed to have adaptations for a partially underground lifestyle. Research published in late 2023 has suggested that Fona played a key role in expanding our understanding of Cretaceous ecosystems, and its significance as an ancestor to Thescelosaurus neglectus, which lived approximately 35 million years later, further highlights its importance in the study of prehistoric life.
“Fona 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,” 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.”
Journal reference:
- Haviv M. Avrahami, Peter J. Makovicky, Ryan T. Tucker, Lindsay E. Zanno. A new semi-fossorial thescelosaurine dinosaur from the Cenomanian-age Mussentuchit Member of the Cedar Mountain Formation, Utah. The Anatomical Record, 2024; DOI: 10.1002/ar.25505