Cochise College           Student Papers in Geology

Geology Home Page                   physical geology  historical geology  planetary  gems           

Roger Weller, geology instructor

by Leslie Evans
Physical Geology
Spring 2013

Gizzard Stones (Gastroliths)

          For all of the unfortunate creatures without teeth, a magnificent organ was developed so that they may digest their culinary delights just as effectively as us superior teeth-bearers. This beautiful organ is known as a gizzard. Wondering how these magical things work? All sorts of animals including birds, worms, seals, and even freaking dinosaurs eat a bunch of rocks on purpose just so that they will get stuck in their little gizzard sacks. But even animals such as crocodiles and alligators have gizzards, and they actually have some pretty impressive teeth. By the way, in all seriousness, it's not even a sack, it's more like a secondary stomach if you're looking for more technical terminology. It is located between the crop and the intestines. (See picture below to know a more visual location of a gizzard) Birds have to swallow eat bite whole, and these rocks grind together, crushing and breaking up their food so they can get their full nutritional benefits and wont have painful bowel movements later. In other words, those rocks act as teeth inside their bellies. What makes a gizzard even more awesome is that they have thick inner membranes, which means the rocks wont rip it open and contaminate their body with all that disgusting business while they're innocently trying to enjoy a meal. The word “gizzard” has a somewhat complicated history, starting with giser to gigeria, but eventually it all comes down to giblets, meaning the edible organs inside of chickens. Yuck!


A description...


     While doing some further research into the subject, I actually found out the reason why crocodiles and alligators need to swallow these rocks! Turns out, aquatic animals actually don't typically use them for grinding up their food like herbivores, but instead use them as ballasts to keep themselves balanced and decrease their buoyancy. This way, the rocks will hold them down just enough so they wont float to the surface and look totally dumb while stalking prey. Without these stones, I can imagine it would be terribly annoying when playing hide-and-go-seek with all of the other water dwellers.

A description...

     The rocks found in gizzards are called gastroliths. Of course, any cool, unusual name like “gastrolith” must come from the Greek language. Gastro is Greek for stomach, while lithos means stone. The size of how big the rocks are depends on the animal, ranging from sand to cobbles. Ostriches have been known to swallow some up to ten centimeters, that's a diameter about the size of an average cellphone. Any kind of rock can become a gastrolith, all they need is to be swallowed by an animal for the specific purpose of being stored inside of their gizzard. Some of these can even be made of petrified wood, seeing how animals can't tell the difference between them and rocks. It can be quite difficult to identify a gastrolith, but one of the ways to tell is if the rock is rounded and polished. It should also be totally unlike all the other rocks in the geological vicinity. For birds, they will swallow sharp, jagged rocks initially. After much use, they eventually start to smooth out and become less useful for grinding, so they will vomit them and find fresh, new ones. An abundance of extinct animals (like dinosaurs) have been found with many of these rounded stones inside of their rib cages. There are many arguments in the archaeological community when it comes to identifying whether or not certain rocks are gastroliths, seeing how many weathering techniques can also round and polish stones. Usually, archaeologists will dismiss any that aren't found near fossil remains.

A description...

     A recent study by Science Daily suggested that, “chickens with bigger gizzards are more efficient”. The idea behind this statement is that chickens will be able to grind their food better, which means they will get more of the nutritional benefits from absorbing it than the chickens with smaller gizzards, because their digestive systems don't work as well. In this study, they raised chickens with larger gizzards and found that they required less food for consumption and produced less waste. This means we wouldn't have to feed them as much nor clean up their poos as often. Researchers say that breeding chickens with this trait would be more economically and environmentally sustainable than the chickens we're currently raising for slaughter. There would be no difference in the meat of their body composition aside from the larger gizzards, so it wouldn't even be like you were eating a terrifying, new, mutant chicken or anything! Who could say “no” to a more efficient chicken?

     This next part may churn your stomach. Chicken and duck gizzards are a popular food dish all throughout the world. They can be found in most butcher shops and grocery stores, some of them already being pre-fried for your convenience in the deli section. You can grill them, pickle them, fry them, boil them, make them into soups, stews, and gumbo. There's a whole universe of gizzard delights just waiting to be discovered by unenlightened palettes! They contain plenty of protein to replenish cells and make up muscle tissue. They're also a great source of iron, zinc, and vitamin B12. This would help with our immune systems, aid in wound healing, promote cell division, and would be great for our neurological functioning. But alas, there are some drawbacks. Although they may be delicacy in some cultures, gizzards are incredibly high in fat content and probably should not be eaten on a regular basis. Eating too many fatty organs like these could potentially lead to gout, also known as “the disease of kings”. If you're anything like me and have no desire to eat gizzards, I suggest taking over-the-counter pills to get the same vitamins and nutrients, you will not be judged.