Fossilized dinosaur eggs discovered in Utah’s Cedar Mountain Formation have unveiled a previously unknown level of biodiversity in North America’s Cretaceous period, offering a glimpse into a world teeming with different species—including an ancient relative of crocodiles never before found outside Europe.

A Fossil Treasure Trove Hidden In Utah

For decades, researchers believed that the Mussentuchit Member of the Cedar Mountain Formation contained only one type of dinosaur egg. That changed when an international team of scientists unearthed over 4,000 fossil eggshell fragments across 20 locations, revealing an unexpected variety of prehistoric life.

Using microscopic analysis and scanning electron microscopy, researchers classified at least six distinct fossil egg species, or ootaxa, proving that multiple dinosaur species coexisted in the region around 100 million years ago.

“The most interesting thing about this for me is the multiple types of elongatoolithid eggshells, which correspond to multiple types of oviraptorosaur dinosaur,” explained  Dr Josh Hedge, a visiting Assistant Professor of Biology at Lake Forest College.

“I think historically we have been guilty of thinking there is one kind of each dinosaur in a given ecosystem, but we are finding more and more that multiple species of each group are likely co-existing. Our analysis suggests that we have at least two or three oviraptorosaurs of different sizes laying eggs in this ecosystem at around the same time,” he added in

Meet The Ancient Parents

The newfound eggshell diversity includes species from the Elongatoolithidae family, linked to oviraptorosaurs, a group of feathered, bird-like dinosaurs. Other eggs belonged to Spheroolithus, associated with ornithopods, plant-eating dinosaurs that walked on two legs.

But perhaps the most surprising find was Mycomorphoolithus kohringi, an egg type previously only found in Europe, indicating that a crocodylomorph, a prehistoric relative of crocodiles, lived in North America during the Cretaceous period.

What This Discovery Means For Dinosaur Science?

This discovery is more than just an addition to the fossil record—it challenges previous assumptions about dinosaur ecosystems. The presence of multiple oviraptorosaur species suggests that dinosaur communities were far more diverse and dynamic than previously thought.

Instead of a one-species-per-habitat model, this research supports the idea that multiple species of the same group coexisted, likely adapting to different ecological niches.

The presence of European crocodylomorph eggs in Utah raises intriguing questions about prehistoric migration patterns and how these species dispersed across continents.

A Richer, More Complex Cretaceous world

Beyond individual species, these fossil eggs offer clues about the broader Cretaceous environment in North America. The diversity of nesting behaviors suggests a thriving ecosystem, with different dinosaurs and reptiles competing for resources, sharing nesting grounds, and potentially interacting in ways paleontologists are only beginning to understand.

With each new fossil discovery, scientists piece together a clearer picture of the ancient world—one where the past is far more complex and interconnected than we ever imagined.

The study, published in PLOS ONE, underscores how even tiny fragments of eggshell can crack open new insights into the prehistoric past.