Eggshells found in Utah fill a 30-million-year fossil record gap and provide a snapshot of a time when dinosaurs were migrating from Asia to North America via a land bridge, according to a paper in PLOS ONE.
The fossils include eggshells from three feathered bird-like dinosaurs, two plant-eating dinosaurs, and one crocodile-like species. It is also the first new dinosaur eggshell discovery from the region in 50 years, as well as the first evidence of a crocodilian species outside of Europe.
A Variety of Dinosaurs
The collection of shells from Utah’s Cedar Mountain from three different kinds of animals represents a wide range of creatures — “one of the best-preserved records of paleobiodiversity in the early Late Cretaceous worldwide,” the paper said.
This variety is important, because it shows that several species of some dinosaurs co-existed. It's a common misconception that only one species of each dinosaur type can exist at a time, says Josh Hedge, a biology professor at Lake Forest College in Illinois and an author of the paper.
"Our data show at least three species of oviraptorosaur and two duck-billed dinosaurs all living alongside each other," says Hedge. "More and more in recent studies we are finding irrefutable evidence of coexisting species of dinosaurs from the same group, and eggshells can help inform us on this."
The period of when the eggs were laid is especially relevant now, because it represents a time just before a major period of global warming.
"This hyperthermal event was the hottest our planet has been in the last 200 million years," says Hedge. "If we want to understand how a warming planet impacted life on land, which is important given our current situation, we have to identify what was alive before and after the event."
Dinosaurs Migrating West
That period was a particularly busy time for dinosaurs. Many species were migrating westward, via a land bridge connecting present-day Russia to Canada. The dinosaurs were possible pioneers in going West, because early humans may have crossed into North America in a similar manner millions of years later. This period of dinosaur dynamism has been labeled the Early Cretaceous Laurasian Interchange Event (EKLInE).
Previous research shows that the new arrivals from Asia eventually pushed out some North American natives. Which dinosaurs appeared where and when is an important part of paleontology. At some point, dinosaur diversity peaked, but began to decline for at least two million years before the creatures went extinct.
Read More: Dinosaur Diversity Was Declining 2 Million Years Before Asteroid Hit
Filling in the Gaps
The story the shells tell fills in a 20-million-year gap of when the “egg thief” oviraptorosaurs arrived in North America and a 15-million-year hole in the arrival of crocodile-like species to the continent.
“Eggshell data are particularly crucial to understanding broader paleoenvironmental questions,” according to the paper. “They provide data points beyond body fossils alone and a fascinating window into the behavioral ecology of these taxa.”
There is a wide diversity of dinosaur eggs, which vary by shape, size, texture, and color. One species was found to have laid 35 — presumably to foil predators. The more eggs one lays, the better chance that at least one offspring will survive. Dinosaur eggs also vary in shape, size, and color. And the largest dinosaurs don’t necessarily lay the biggest eggs. Examining fossilized dinosaur eggshells can help us piece together more information about the extinct creatures.
"Eggs and eggshell fossils are important!" says Hedge. "While finding dinosaur bones is obviously useful, finding eggshells can tell us something about both dinosaur reproductive/nesting behavior and fill some gaps about the ecosystem when dinosaur bones might not be found."
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Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
