Minda Berbeco's picture

Answer Monday!

Last week on Fossil Friday, I presented you with a tricky identification task. This egg-shaped rock was far afield from the jaws, spines and shells you've been used to.

So what was this unique rock? It was a dinosaur gastrolith from the late Jurassic!

What is a gastrolith?

From the UCMP:

"Lots of animals eat rocks. Or at least they swallow rocks; they don't eat them in the sense of digesting them. This is true of many reptiles and birds that are alive today, and a few mammals such as seals and whales. It was also true of some extinct animals, including herbivorous dinosaurs and marine reptiles. Rocks that have been in the digestive system of an animal are called gastroliths, which literally means 'stomach stones.' "

So, how can you tell a gastrolith from just some random rock?

"Sometimes a fossil skeleton is found with a pile of pebbles or small rocks inside the rib cage, or scattered around the body. These rocks are usually pretty easy to identify as gastroliths. The only other thing they could be is stream pebbles that washed up against the body of the animal as it was being buried under sand and silt. Paleontologists compare the rocks to others in the same formation to see if they could have washed in from someplace else, or if they are really gastroliths. This is usually only necessary if the gastroliths are scattered. If the rocks are found in a nice tight pile in the rib cage, they are almost certainly gastroliths."

I've seen some cool, crazy and unusal things since starting Fossil Friday, but to be honest, gastroliths take the cake.  So who was the first to identify this ol' rock?  Gerald Wilgus, a regular commenter on the Fossil Friday. Kudos to Gerald!

Gerald, any special requests for next week?  How about something...mammalian for a change?