Given that the recent theropods – the birds – lay eggs, it’s hardly surprising that the non-bird dinosaurs laid eggs too. But what do we actually know about the eggs of the non-bird dinosaurs? What can they tell us about dinosaur reproduction and biology in general?
Daniel Barta (*1 May 1989) is an American paleontologist who is currently a Ph.D. candidate at the Richard Gilder Graduate School at the American Museum of Natural History. From a broader perspective, Daniel studies dinosaur growth and development. He earned his master’s and bachelor’s degrees from Montana State University, and published on dinosaur eggs from the Cretaceous of China and Mongolia.
Daniel Madzia: What can we learn from studying dinosaur eggs?
Daniel Barta: Dinosaur eggs are a unique source of information about nesting behavior and reproductive biology. Nest structures and the arrangements of eggs within clutches can be thought of as trace fossils, whereas the eggs themselves are body fossils. Studying adult-clutch associations and clutch sizes can reveal much about the type of parental care and amount of reproductive investment offered by dinosaur parents; these are both important components of any animal’s life history. Additionally, isotopic studies of dinosaur eggshell have been used to infer the body temperature at which the eggs formed inside the mother dinosaur, which may help us to understand dinosaur metabolism. Other isotopic work has used oxygen and carbon stable isotopes from dinosaur eggshell as proxies for paleoenvironmental conditions. Eggs can also reveal the presence of a general type of dinosaur or other animal at a locality from which its bones are not yet known, and are therefore important for studies of faunal diversity and distribution.
DM: Why did you decide to work on dinosaur eggs?
DB: During my undergraduate and master’s studies at Montana State University, I became fascinated by the potential that dinosaur eggs have for revealing aspects of dinosaur biology and evolution that we can’t understand from bones alone. Fossil eggs remain relatively understudied, and there is a lot more to be learned about dinosaur eggs along all of the lines of research I named and more!
DM: Can you describe how the research of dinosaur eggs looks like?
DB: My work on dinosaur eggs largely involves describing the microscopic structure of their eggshell with both light microscopy and scanning electron microscopy.
DM: Are the dinosaur eggs easily distinguishable from the eggs of their close relatives – pterosaurs and crocodiles and their kin?
DB: Dinosaur eggs are fairly easily distinguishable from the eggs of pterosaurs and crocodiles. Pterosaurs had leathery, poorly mineralized or thin eggshells, whereas crocodile and dinosaur eggs are typically more extensively mineralized. Crocodile eggs and dinosaur eggs differ greatly in the specific arrangement of the calcite crystals that make up their eggshell. Turtle eggshell is further distinguished from all of these other eggshell types because it is composed of aragonite instead of calcite.
DM: How often do we find dinosaur eggs with babies preserved well enough to be studied?
DM: Dinosaur embryos and hatchlings are extremely rare to find. Paleontologists have bones from these life stages for just over a dozen out of the hundreds of known species of dinosaurs.
DM: A recent paper on the incubation time of dinosaur embryos argued that some dinosaur eggs took as long as six months to hatch. Comparing to the incubation time of birds, whose eggs usually take the first few weeks to hatch, it’s a pretty long time. What’s your opinion on these results?
DB: I think this research takes a really novel approach to the study of dinosaur development. The major finding that dinosaurs had long, reptile-like incubation periods reminds us that dinosaurs were not exactly like either modern birds or modern reptiles in all aspects of their biology—they were both unique and transitional in many ways.
Featured image © Daniel Barta.