Ninety-one million years ago, water split North America in half, running from the Arctic Ocean in the north to the Gulf of Mexico in the south. At this time, sea levels were high across the globe, and as they rose, water inundated the center of present-day North America. Terrestrial environments along the late Cretaceous Epoch “coastlines” were wiped away by rising tides.
These high sea levels down the middle of the continent left a legacy of marine fossils and rocks, preserving water-based fish and fowl that paleontologists are finding today—which makes one area in west-central New Mexico all the more valuable to paleontologists and other dinosaur hunters.
Since 1996, researchers at the Zuni Basin Paleontological Project have uncovered and identified numerous familiar and brand-new specimens, from the Zuniceratops to petrified wood.
Now, Andrew McDonald, a Penn Ph.D. student in the Department of Earth and Environmental Science, has described a new species of dinosaur originally found at the site in 1996. Called Jeyawati [pronounced HEY-a-WHAT-ee] rugoculus, the herbivore dinosaur comes from rocks that also preserve a swampy forest ecosystem that thrived near the shore of a vast inland sea 91 million years ago.
Jeyawati was actually the first dinosaur found at the site, says McDonald, but was overshadowed by other spectacular finds in the United States, like the T-Rex discovered in South Dakota in 1990.
McDonald, the lead author on a paper about the identification published in the May issue of Vertebrate Paleontology, says he began examining the bones in 2006, while an undergraduate at the University of Nebraska. He completed the project with Peter Dodson, professor of anatomy and paleontology in Penn’s Vet School and School of Arts and Sciences. This project was McDonald’s first serious research undertaking.
“I familiarized myself with the literature on this group of animals, what features distinguished the species,” says McDonald. “It was clear there were certain features in the specimen that were unique.”
Specifically, one of the bones that formed the Jeyawati’s eye socket exhibited a rough or wrinkly texture on its outer side, suggesting that the dinosaur may have had one or more scales above and behind its eye. The dinosaur is a close relative of the duck-billed hadrosaurs, which were abundant across the Northern Hemisphere for much of the Late Cretaceous Epoch, between 80 and 65 million years ago, but Jeyawati retains some primitive features of the teeth and jaws that preclude it from being a fully-fledged hadrosaur.
Jeyawati likely walked on four legs, but was capable of rearing up onto two legs—an assumption made after close examination of the more complete remains of species related to the new dinosaur. McDonald notes that it is difficult to pinpoint the exact size of Jeyawati. But he says it was probably between four and five meters (between 13 and 16 feet) in length.
The first part of the dinosaur’s name, Jeyawati, is derived from two words in the language of the Zuni people, a Native American tribe located around the site, and translates to “grinding mouth.” The second part of the name, rugoculus, comes from the Latin words ruga and oculus, and means “wrinkle eye,” describing a unique feature of the new species.
In order to identify Jeyawati’s remains as those of a unique species, McDonald compared skull bones, vertebrae and skull fragments to specimens from other species.
McDonald says it took him about a year to realize that he was looking at a dinosaur that was previously unknown to researchers.
In his research, McDonald was able to discern that Jeyawati had a difficult life. “Some of these rib fragments have a strange rough bulbous texture on them,” he says, which told him that Jeyawati had suffered broken ribs at some point in its life and those injuries had healed before its death.
McDonald says the dinosaurs identified at the New Mexico site are the earliest and most primitive ancestors of Triceratops and Tyrannosaurus. “This animal that I worked on is pretty close to being a duck-billed hadrosaurus,” says McDonald. “[Jeyawati] is kind of a transitional animal."
For his dissertation, McDonald will continue to examine Jeyawati and other members of the Basal Iguanodon lineage of dinosaurs, in order to figure out the worldwide evolutionary relationship of these animals.
Originally published on June 10, 2010