Slow Growth of Dinosaur Embryos – #365papers – 2017 – 5

#365papers for January 5, 2017

Erickson, Zelenitsky, Kay, and Norell, 2016, Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth show reptilian-grade development: Proceedings of the National Academy of Sciences.

What’s it about?

This paper discusses the use of growth lines in teeth to determine how long an animal was in its egg before hatching. We know already at what point during development that teeth begin to grow. All teeth preserve fine growth lines that form daily, and by counting the lines on teeth found in dinosaur eggs that appear ready to hatch, we can get a sense of how long the animal was in the egg from being laid to hatching.

The surprise was that dinosaur eggs were incubated for several months (estimates are 2.8 to 5.8 months), which is similar to modern reptiles. This is radically different than the incubation times of modern birds that range from 11-85 days (less than two weeks to about 2.5 months).

Why does it matter?

It has been assumed that because modern birds have short incubation times (that is, rapid embryonic development), dinosaurs did as well. With this new evidence, it’s possible that the decline of dinosaurs was related to their very slow development rates.

Why did I read this?

I read this because it was popping up all over my Twitter and Facebook feeds. It generated a lot of interest in the paleontological community, so I felt I would benefit from reading it. As it happens, I additionally have a great interest in the growth and mineralization of teeth, so I wound up really enjoying this paper from that perspective.