In a paleontological breakthrough, a recently unearthed plant-eating dinosaur has shed light on the final stages of a species struggling to adapt during a time of significant climate change.
The skeletal remains of a juvenile dinosaur, known as Iani smithi, including its skull, vertebrae and limbs, were recovered from Utah's Cedar Mountain Formation. This early ornithopoda dinosaur, named after Janus, the Roman god of change, offers valuable insights into the massive population shifts among dinosaurs triggered by the Earth's warming climate.
Iani smithi thrived approximately 99 million years ago during the mid-Cretaceous period, in what is now Utah. What distinguishes this dinosaur is its formidable jaw, featuring teeth perfectly evolved to tear through robust plant material.
Finding Iani was a streak of luck,” said study author Lindsay Zanno, associate research professor at North Carolina State University and head of paleontology at the North Carolina Museum of Natural Sciences.
“We knew something like it lived in this ecosystem because isolated teeth had been collected here and there, but we weren’t expecting to stumble upon such a beautiful skeleton, especially from this time in Earth’s history. Having a nearly complete skull was invaluable for piecing the story together.”
The mid-Cretaceous period witnessed dramatic changes that significantly impacted dinosaur populations. Rising atmospheric carbon dioxide levels led to a global temperature increase and subsequent rising sea levels, confining dinosaurs to shrinking landmasses.
The poles experienced such warmth that rainforests thrived, while coastal areas were dominated by flowering plants that replaced traditional herbivore food sources.
The once-dominant giant plant-eating sauropods and their allosaurian predators disappeared in North America. Concurrently, smaller herbivores migrated from Asia, like early duckbill and horned dinosaurs, alongside feathered theropods such as tyrannosaurs and massive oviraptorosaurs.
Iani smithi stands out not only as a recent discovery but due to its rarity within the North American fossil record. This cements its unique position in the annals of dinosaur history.
Utilizing this preserved specimen, Zanno and her team delved into the evolutionary relationships of Iani, yielding surprising and somewhat skeptical findings.
"We recovered Iani as an early rhabdodontomorph, a lineage of ornithopods known almost exclusively from Europe," Zanno said.
"Recently, paleontologists proposed that another North American dinosaur, Tenontosaurus—which was as common as cattle in the Early Cretaceous – belongs to this group, as well as some Australian critters. If Iani holds up as a rhabdodontomorph, it raises a lot of cool questions."
Foremost among these inquiries is whether Iani represents the final gasp of a once-flourishing lineage. Zanno thinks studying this fossil in the context of environmental and biodiversity changes during the mid-Cretaceous will give us more insight into Earth's history.
“Early ornithopods were once a common part of North American ecosystems, but we did not know they survived into the Late Cretaceous,” the authors noted.
“The discovery of Iani helps us link their extinction on the continent with a major interval of global warming, one with striking similarities to our current climate crisis.”
The study was published in PLOS ONE.