This new dinosaur species thrived at the cusp of major planet changes due to warming

“Finding Iani was a streak of luck. 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,” said Lindsay Zanno, associate research professor at North Carolina State University, head of paleontology at the North Carolina Museum of Natural Sciences, and corresponding author.

During the mid-Cretaceous period — around 99 million years ago — the species existed in Utah. 

This was a period when the Earth experienced a major climate shift. Increased carbon dioxide in the atmosphere caused substantial warming, gradually resulting in sea-level rise. Back then, the warming was so intense that rainforests occupied the Earth's poles, which are today covered in ice. 

All of these changes had a significant impact on dinosaur numbers. The dinosaurs were forced to shift as landmasses shrank, jeopardizing their existence.  

For example, giant plant-eating sauropods and carnivores allosaurs began to vanish from North America. At the same time, smaller dinosaurs from Asia arrived, including duckbills, horned dinosaurs, and feathered theropods (tyrannosaurs and massive oviraptorosaurs). 

Evolutionary relationships

The team used the recovered specimen to trace the evolutionary relationships of Iani. 

“We recovered Iani as an early rhabdodontomorph, a lineage of ornithopods known almost exclusively from Europe,” Zanno mentioned in an official release. “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.”

This early ornithopod is a member of the dinosaur lineage that gave rise to duckbill dinosaurs like Parasaurolophus and Edmontosaurus.

According to the authors, Iani was potentially the only surviving member of an ornithopod lineage that previously ruled areas of North America. The species ultimately pave the way for the arrival of duckbill dinosaurs.

“Iani was alive during this transition – so this dinosaur really does symbolize a changing planet. This dinosaur stood on the precipice,” said Zanno. 

The study has been published in the journal PLOS ONE. 

Study abstract:

Intensifying macrovertebrate reconnaissance together with refined age-dating of mid-Cretaceous assemblages in recent decades is producing a more nuanced understanding of the impact of the Cretaceous Thermal Maximum on terrestrial ecosystems. Here we report discovery of a new early-diverging ornithopod, Iani smithi gen. et sp. nov., from the Cenomanian-age lower Mussentuchit Member, Cedar Mountain Formation of Utah, USA. The single known specimen of this species (NCSM 29373) includes a well-preserved, disarticulated skull, partial axial column, and portions of the appendicular skeleton. Apomorphic traits are concentrated on the frontal, squamosal, braincase, and premaxilla, including the presence of three premaxillary teeth. Phylogenetic analyses using parsimony and Bayesian inference posit Iani as a North American rhabdodontomorph based on the presence of enlarged, spatulate teeth bearing up to 12 secondary ridges, maxillary teeth lacking a primary ridge, a laterally depressed maxillary process of the jugal, and a posttemporal foramen restricted to the squamosal, among other features. Prior to this discovery, neornithischian paleobiodiversity in the Mussentuchit Member was based primarily on isolated teeth, with only the hadrosauroid Eolambia caroljonesa named from macrovertebrate remains. Documentation of a possible rhabdodontomorph in this assemblage, along with published reports of an as-of-yet undescribed thescelosaurid, and fragmentary remains of ankylosaurians and ceratopsians confirms a minimum of five, cohabiting neornithischian clades in earliest Late Cretaceous terrestrial ecosystems of North America. Due to poor preservation and exploration of Turonian–Santonian assemblages, the timing of rhabdodontomorph extirpation in the Western Interior Basin is, as of yet, unclear. However, Iani documents survival of all three major clades of Early Cretaceous neornithischians (Thescelosauridae, Rhabdodontomorpha, and Ankylopollexia) into the dawn of the Late Cretaceous of North America.