Utah was a hotbed of dinosaur diversity during the Late Cretaceous period, and paleontologists have the fossilized eggshells to prove it. Researchers led by former NC State Ph.D. student Josh Hedge uncovered six new types of eggshells from the Mussentuchit Member of Utah's Cedar Mountain Formation. Three of the samples came from oviraptorosaurs (feathered, bipedal omnivores), two from ornithopods (plant-eaters like hadrosaurs) and one from a crocodylomorph, or early crocodile relative.
The Abstract sat down with co-author Lindsay Zanno, associate research professor at NC State and head of paleontology at the North Carolina Museum of Natural Sciences, to talk about the finding and what it means.
The work appears in PLOS One. Hedge is currently at Lake Forest College.
The Abstract (TA): The eggshells you recovered came from the Mussentuchit Member in Utah. What makes this area so special, paleontologically speaking?
Zanno: The ecosystem preserved by the Mussentuchit Member of the Cedar Mountain Formation is our best window into what western North America looked like at the dawn of the Late Cretaceous (about 100 - 66 million years ago). We have been discovering and identifying the plant and animal species that lived there as part of a major research project for over a decade. This is important because at the time these species were alive, Earth was about to enter a major interval of global warming. In fact, this "hyperthermal" event was the hottest our planet has been in the last 200 million years. 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.
TA: Why would we look for eggs or shells, rather than bigger remains? What can these fossils tell us?
Zanno: Everything we know about ancient life comes from remains preserved in the fossil record, but different types of fossil evidence are subject to different preservational biases. If we want to reconstruct long-lost ecosystems, we need to study more than just the skeletons of the dead, we need to study the traces of their lives. These different biases mean that trace fossils sometimes reveal evidence of species that body fossils do not, helping us fill in the overall picture. We're lucky that a variety of dinosaurs once nested and raised their young in the area now called the Mussentuchit, giving us a peek into the world of dinosaurs not commonly seen.
TA: How can you tell which species go with the shells? And can you determine specific dinosaurs from the shell type, or is it more general? For example, we know these are tyrannosaurids, but not necessarily T. rex, that kind of thing?
Zanno: Generally, eggshells can only tell us broadly about the group of dinosaurs producing them. Sometimes even that is difficult because the connections have to be based on incredibly rare fossils that preserve bodies and eggs in association. In this case, though, we can tell that at least three species of one group of oviraptorosaurs inhabited the Mussentuchit ecosystem. So even if we can't tell which exact oviraptorosaur species each eggshell type belonged to, the eggshell gives us clues about the diversity of the area that we can't get from the skeletons alone.
TA: What was the most interesting or unusual aspect of this find?
Zanno: We knew that oviraptorosaur diversity was high in the latter part of the Cretaceous. This research tells us that multiple species lived alongside one another in Cretaceous ecosystems of North America for 20 million years longer than we previously knew. Fossil eggshell of crocodiles is also rare, and we were super excited to find and describe some examples. The eggshell is so remarkably thin that only our keenest-eyed team members (read youngest… cough cough) could even spot it in the quarry!
TA: Is it possible that finding these eggs could clue us in to the existence of undiscovered dinosaur species?
Zanno: In fact, several of these eggshells were produced by dinosaurs and crocodiles that don't yet have a name. Until now, scientists haven't had enough skeletal material to name them. But we now have some skeletons in preparation at NC State's joint paleontology lab at the North Carolina Museum of Natural Sciences in downtown Raleigh, so several of them will have their day in the spotlight soon. Stay tuned!
