Some dinosaur eggs took a surprisingly long time to hatch, according to a study published Monday in the journal Proceedings of the National Academy of Sciences. By examining the teeth of unhatched dinosaur embryos, paleontologists determined that one species spent about three months incubating, while another spent six.
Fossils of dinosaur eggs might be common, but embryos are very rare. “Virtually nothing is known about their embryology,” coauthor Gregory M. Erickson of Florida State University, told the New York Times.
But dinosaur eggs can shed light on the creatures’ evolution, behavior, and how they went extinct. Here are six things we have learned from dinosaur eggs—and from the occasional lucky embryo.
