A Peek Inside an Anole

Three different individuals of Anolis cybotes that appear to have small pebbles or debris in their guts.

Three different individuals of Anolis cybotes that appear to have small pebbles or debris in their guts.

While analyzing some xrays of Anolis cybotes for my thesis work, I came across a few specimens that appear to have small dark masses in their guts. The numbers are pretty low – in over 200 xrays, I can only detect these masses in a handful of individuals. My curiosity was piqued. At first glance, they look like they might be gastroliths. Gastroliths, or gizzard stones, are rocks that animals eat to aid in digestion. Basically, the rocks help manually grind the food into smaller bits in a special portion of the digestive track called the gizzard. We know that many archosaurs (crocodilians, dinosaurs [including birds], and pterosaurs) have gizzards. Dinosaur gastroliths are some of my favorite fossils because they are usually polished and quite beautiful. However, unless I’m mistaken, lepidosaurs (squamates and rhynchocephalians) don’t have gizzards and aren’t known to have gut stones. Does anyone have an idea about what this could be? It’s possible that these are just accidental ingestions of small pebbles. Anolis cybotes do often forage near or on the ground, so perhaps it’s not so far-fetched for them to pick up a little rocky debris.

Also, check out this image of a regenerated tail!

Anolis cybotes with a regenerated tail.

Anolis cybotes with a regenerated tail.

About Martha Muñoz

Martha is a postdoctoral researcher in Sheila Patek's laboratory at Duke University. She received her Ph.D. at Harvard University, where she studyied the evolutionary ecology and thermal physiology of anoles, focusing on the cybotoid anoles from the Dominican Republic. Martha serves as Conference Editor for the Anole Annals. Website: www.marthamunoz.weebly.com

9 thoughts on “A Peek Inside an Anole

  1. Snails? Seeds? I’ve found quite a few snails in anole stomachs (both equestris and sagrei), but never any ‘rocks’. It’s difficult to tell from the images, but snails do show-up rather well in X-rays and you can usually make out the whorls and aperture.

  2. Martha,
    These are likely small stones. My guess is that sand or pebbles are taken accidentally when grabbing prey. I see this a lot in geckos, maybe 1/4 to 1/3 of specimens of some species have these small solid objects in the abdomen (see photo). It is probably less common in Anolis if they are taking prey on tree trunks or on top of leaves, if on the ground. Incidentally, many gecko species will just eat dirt and soil, likely to obtain minerals, so that may also explain a higher frequency in geckos.
    Very cool stuff!!!

    1. Tony did I send you that image? I have several x-rays of Sphaerodactylus that contain bits of gravel like the ones posted.

      Also this:

  3. I agree with Tony. During our first attempts at keeping anoles in a university animal care facility we used fine gravel on the cage bottoms (it satisfied the need for something that could be sterilized). Small pebbles ended up in the stomachs of many lizards and within a few months we moved away from this option.

  4. Hi All,
    Thanks for your thoughts and awesome images. I agree with the suggestion above that it’s likely small stones that were accidentally picked up during foraging. By the looks of it, this occurs fairly regularly. Tony’s most recent image was especially interesting to me because I have a few specimens with little bits sprinkled throughout their guts, as well. By the way, is this the first use of the term ‘gut luggage’? Hilarious. We should keep it.

  5. Like Tom, we occasionally had lizards in our colony eating cage substrate (organic soil in our case), in a seemingly intentional way. Often these were sick animals, and I found some dead animals with their mouths completely stuffed with soil. I imagine if we had small rocks available they would have wolfed them down too. A vet we worked with once suggested this might be a manifestation of pica.

  6. When we were regularly doing stomach content analyses, bits of grit were not uncommon in anoles, but were more likely to show up in trunk-grounds than in the other ecomorphs. Interestingly, we tended to find more “luggage” in anoles than in ground-dwelling Leios or Ameivas, which we had not expected.

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