One is a giant nearly foot-long egg found by a Chilean scientist in Antarctica helps answer that question. The egg that looks like a deflated football suggests that mosasaurs didn’t give live birth but laid leathery-shelled eggs similar to their closest living relatives monitor lizards and snakes. These soft eggs tend to rot away quickly and can also explain why they are less likely to become fossilized. This giant egg was actually found in 2012 but was put aside and labeled “The Thing”, not knowing what it was until recently. Many dinosaurs lay hard shelled eggs similar to today’s birds.

Read more about it: https://www.smithsonianmag.com/smart-news/first-soft-shelled-dinosaur-eg...

https://scitechdaily.com/the-thing-analysis-of-mysterious-giant-egg-the-...