About 100 million years ago in what is now Utah, a 10-foot-long (3-meter-long) cousin of duck-billed dinosaurs pulverized tough plant stems and leaves with its robust teeth and powerful jaws.
It probably was too busy chewing to notice that the once-familiar world around it was transforming. But for the scientists who recently described this newfound species, its fossils offer clues about life during the middle of the Cretaceous Period (145 million to 66 million years ago), as rising air temperatures and sea levels reshaped leafy habitats on land.
Analysis of the bones surprised them — the animal appeared to be a close relative of rhabdodontomorphs, a type of ornithopod previously known almost entirely from European fossils.
Investigating a new species
“This new fossil suggests that species of Rhabdodon-like ornithopods were more diverse and lingered around longer in North America than previously realized,” Zelenitsky, who was not involved in the study, told CNN in an email.
The dinosaur’s genus name — Iani — is a nod to its changing world. It references the two-faced Janus, the Roman god of transitions, the study authors reported.
Paleontologists excavated the fossils in 2015 at a site called the Mussentuchit Member in southern Utah, said lead study author Lindsay Zanno, head of paleontology at the North Carolina Museum of Natural Sciences and an associate research professor in biological sciences at North Carolina State University in Raleigh.
The bones included a skull, some ribs and vertebrae, limb bones and parts of the pelvis. Well-preserved Cretaceous skulls from this part of North America are extremely rare; the region once bordered a vast inland sea, and bones fossilize poorly in coastal humidity, Zanno told CNN in an email.
“The bones of its spine are not fused together, leaving room for it to grow,” Zanno explained.
Because rhabdodontomorphs are known almost exclusively from Europe (with some possible species identified in Australia), the scientists weren’t expecting to find one in late Cretaceous deposits in North America.
However, a number of features in the animal resembled those of rhabdodontomorphs, including unique cheekbones; large, deeply ridged teeth; and the position of an opening in the skull for an artery. Other features, such as the shape of the braincase and palate, and the positions of teeth toward the front of the face, indicated that it was a new species.
Hadrosaurs, which evolved tens of millions of years after I. smithi, adapted to share ecosystems with tyrannosaurs, some of the fiercest land predators ever known. And they managed to do so without the benefit of horns or armor that protected other herbivorous dinosaurs, Zelenitsky said.
“Perhaps ornithopod species evolved a certain way or adopted certain behaviors to succeed,” she said. “Primitive forms, like Iani, are near the root of the ornithopod evolutionary tree and surely will provide some answers.”