MadSci Network: Evolution

Re: What are the identifying traits of a gastrolith?

Date: Wed Nov 10 10:35:13 1999
Posted By: David Kopaska-Merkel, Staff Hydrogeology Division, Geological Survey of Alabama
Area of science: Evolution
ID: 941737737.Ev

Dear Yvonne:

I am not an expert on dinosaurs; for that, I suggest you contact the National Museum of Natural History of the Smithsonian Institution in Washington DC ( They will be able to give you all the help you need in this area. However, I can at least partly answer your question. Gastroliths are often identified when skeletons are collected because they are actually found INSIDE the skeleton in the gizzard area. Typically, gizzard stones found within dinosaur gizzards are dramatically different from any stones in the rock surrounding the dinosaur skeleton. Three lines of evidence lead to the inference that such stones are gizzard stones:

  1. The living descendants of dinosaurs (birds) use gizzard stones
  2. The stones are found where the dinosaur's gizzard was
  3. There aren't similar stones lying around that could have "somehow" gotten into the gizzard without being gizzard stones.

It is my understanding that certain physical features of the surfaces of gizzard stones help specialists identify them even when they are not actually found inside dinosaur gizzards, but I don't know what those physical features are.

As for your reference to an age of 10,000 years, this is not relevant, because the youngest known dinosaurs are about 65,000,000 years ago (plus or minus a couple of 100,000 years). Even this is not relevant to the question of identifying gizzard stones, which rests solely on physical evidence, and the inference that dinosaurs and birds may share behaviors because they are related and appear to have occupied some of the same ecologic niches.

Best Regards,
David C. Kopaska-Merkel
Geological Survey of Alabama
PO Box 869999
Tuscaloosa AL 35486-6999
(205) 349-2852
FAX (205) 349-2861
web site:

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