100-million-year-old dinosaur eggs recovered in Jurassic America

Central Utah, 100 million years ago, was a very different place–covered in forests and water. It was a lush, watery landscape on the edge of the Western Interior Seaway. In this landscape, dinosaurs and early mammals drank from the same water sources, while ancient crocodiles hid beneath the surface, to attack their prey. Dense forests and rivers supported a wide variety of life. This region was part of a dynamic ecosystem where survival depended on constant adaptation. Recent fossil discoveries from the Mussentuchit Member of the Cedar Mountain Formation—including bones and broken eggshells—offer a rare glimpse, helping scientists understand the creatures that once thrived in this ancient, ever-changing environment.4000 dinosaur eggshell fragments found buried in 20 sitesFor over a year, paleontologists assumed that there was just one type of dinosaur egg buried in the sediments.According to earth.com, their assumption was proven wrong after the researchers collected more than 4,000 eggshell fragments from 20 sites and examined them under scanning electron microscopes and light microscopes. As the eggshells split into at least six distinct ootaxa- a scientific term for fossil egg species, showed that several different animals shared the same nesting grounds.

“The most interesting thing about this for me is the multiple types of elongatoolithid eggshells, which correspond to multiple types of oviraptorosaur dinosaurs”, shared Dr. Josh Hedge, a visiting assistant professor of biology at Lake Forest College.He added, “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 coexisting.”Their research suggests that at least two or three oviraptorosaurs of different sizes were laying eggs in that Utah ecosystem at the same time.

Dinosaur egg diversity

Many of the eggshells found belonged to feathered dinosaurs called Oviraptorosauras. These eggs were long and narrow, similar to the modern bird eggs, a shape that might have helped the embryos breathe while buried in warm sand. Other eggs belonged to plant eating dinosaurs that walked on two legs called Ornithopods. But perhaps the most surprising find was Mycomorphoolithus kohringi, an egg type previously found only in Europe, indicating that a crocodylomorph, a prehistoric relative of crocodiles, also lived in North America during the Cretaceous period.

About the egg layers

Most Oviraptorosaurs were mid-sized, feathered omnivores with strong beaks and stubby tails. Among the recent skeletal finds, Moros, a horse-sized early tyrannosaur, and lani, a beaked plant-eater were also found. Meanwhile, Ornithopods were the workhorses of the Cretaceous West. They left abundant tracks but rarely complete skeletons. They were dry-season grazers or wet-season browsers.Their thick-walled eggs support the idea that they buried their clutches in vegetation, much like today’s megapode birds.

What eggs clue about the ancient ecosystem

Clutch spacing, shell thickness , and pore patterns tell us about the soil moisture, vegetation cover, and parental care behaviors.The six ootaxa signify: shallow buried mounds for crocodile cousins, sand plastered rings for oviraptorosaurs, and leaf-blanketed pits for ornithopods.Microscopic and scanning electron analysis revealed crystallite patterns thinner than a human hair, allowing the scientists to match tiny fragments to broader evolutionary groups.This wide variety suggests the characteristics of an ecosystem, rich in microhabitats, where animals could partition the resources and thrive side by side.