For as long as I can remember, I have suffered from a weak stomach (officially, gastroparesis). It’s terribly uncomfortable and makes eating a chore, if not something to fear, because I never know when my stomach will fail me. For many like me, there are medications to promote stronger muscle response and aid in digestion. But even when medication doesn’t help, as is frequently the case, I am still able to say, “Hey, it could be worse. At least I don’t have to swallow rocks to help finish my meal.”
Gastroliths within the rib cage of an Elasmosaurus. Image from the Royal Tyrrell Museum exhibitions page.
That’s right! Swallowing rocks is one of the most innovative techniques in nature for enhancing digestion. For many of Earth’s residents, these ‘stomach stones’, also called gastroliths, provide abrasive surfaces to grind their food to a digestible consistency. Over time, these rocks are rounded and polished, much like cobbles in a river. But what happens when the animal dies?
Just like any durable stone or bone, gastroliths have a relatively high potential for preservation in the rock record. Thousands (or millions?) have been recovered, mainly for their role as collectibles. Of these, many are associated with various dinosaurs (e.g. Psittacosaurus) from the late Mesozoic, about 70–170 million years ago. Therefore, gastroliths also have incredible value for paleontologists, who are constantly searching for clues into the behavior and biological details of ancient animals.
Originally termed and described by Barnum Brown in 1904, who cited ‘stomach stones’ as evidence for the dietary habits of ancient plesiosaurs, gastroliths were met by a dose of skepticism. It wasn’t immediately clear (or convincing) to early paleontologists that these stones were derived from the stomachs of animals, let alone dinosaurs. But as more fossil sites were discovered, some of which contained polished stones still within the rib cage of intact dinosaurs, the association became unequivocal.
Now, what does any of this have to do with Young-Earth Creationism and Flood geology? In my 100 Evidences that the Earth is Old, syntectonic deposits made the list at #37, because these sedimentary deposits contain weathered, polished fragments of rock from lower in the geologic column. In other words, Paleozoic (542–251 Ma) rocks had to solidify completely, breakdown into smaller clasts, become rounded and smoothed by abrasion, and then reworked into conglomerates of Mesozoic and Cenozoic age. This relationship tells us that the geologic column could not have been deposited collectively within a short period of time, no matter how large the catastrophe.
Gastroliths are no different, in that the rock formations from which they are derived had to solidify completely and weather out before they could be consumed by dinosaurs and other ancient animals. However, this line of reasoning is especially persuasive when gastroliths themselves contain fossils of Paleozoic life forms! As Stokes (1987) observed in Late Cretaceous gastroliths in Utah:
An unusual feature of gastroliths is their content of derived or reworked fossils. In specimens collected by the author the rough order of decreasing abundance is brachiopods, sponges, corals, fusulinids, petrified wood, bryozoans, and molluscan fragment.
In other words, these dinosaurs were themselves ancient fossil hunters, sampling everything from molluscs that lived in the Ordovician oceans to trees buried in the Upper Triassic Chinle Formation. Added to that list are orange cherts characteristic of the underlying Kaibab Formation. So how did all these fossils end up in the stomachs of dinosaurs, who—according to Ken Ham—were buried in the same catastrophic flood as all Paleozoic life forms?
Perhaps in the beginning stages of the flood, some marine and terrestrial life forms were buried in sediment, which immediately hardened into solid rock. A few days later, the rock was broken up into neat little cobbles, which were consumed by hungry dinosaurs with weak stomachs. Then accelerated digestive decay turned these cobbles into polished, rounded, fossiliferous stones, which are now preserved in the rib cages of well known dinosaurs like the one below…right?
Gastroliths preserved in situ in a specimen of the small theropod Caudipteryx zoui. Image of the display at Carnegie Museum of Natural History reproduced from The Great Cretaceous Walk.
No. Dinosaurian gastroliths don’t simply contradict the Flood geology paradigm. They make it look downright silly.
Feature Image: “Psittacosaurus stomach stones” by Ryan Somma, via Wikimedia Commons
Age of Rocks 
It could be reworked so that after the animals died, the waters would’ve polished the stones relatively quickly, in several days, could it?
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Great observation, and you’re absolutely right (though it would take more than a few days). I think this was a major reason for early skepticism, but it’s been tested in two ways.
First, the gastroliths found still inside dinosaur skeletons could not have been reworked. Using those samples, as well as modern stomach stones, more recent research has utilized electron microscopy to examine very precise details on the surface of the stones, which actually distinguish them from, say, river-polished pebbles. This way, even reworked gastroliths can still be identified as such.
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