Digestive Anatomy and Physiology of Dinosaurs

You think this is a joke, don't you? How can we possibly know anything about the digestive physiology of creatures that last walked the earth 65 million years ago? It is true that not much is known, but paleontologists are clever and patient, and have made some interesting discoveries and deductions.

It is now widely accepted that birds evolved from a group of two-legged dinosaurs known as theropods and it therefore might be expected that dinosaurs had a digestive system similar to birds. Indeed, there are several pieces of evidence from fossils supporting just this hypothesis.

• The skeleton of a Daspletosaurus, a large carnivore closely related to T. rex, was found in Montana that contained fossilized gut contents (Varriccio 2001). These remains of the animals digestive tract revealed acid-etched vertebrae and teeth from what appeared to be a juvenile duck-billed dinosaur (Hadrosaur), suggesting that Tyrannosaurids digested their prey using digestive processes similar to what occurs in modern day birds and crocodilians.
• Anchiornis was a small dinosaur with feathered wings that lived roughly 150 million years ago. Fossils of this dinosaur discovered in China contain what appear to be gastric pellets composed of fish bone and scales (Zheng et al. 2018). In modern birds, gastric pellets are formed from indigestible material by compaction in the gizzard, so this finding supports the contention that many dinosaurs had an avian-like digestive anatomy and function.
• Many modern birds ingest small stones that remain in their muscular stomach (gizzard) as "gastroliths" and likely aid in grinding and thereby enhancing digestion of fibrous plants. There have been multiple reports of clusters of smooth stones being found in the abdominal cavity of large sauropod dinosaurs and it has been assumed they served the same purpose as is seen in birds. There is some controversy over whether these purported dinosaurid gastroliths indeed had the same gastric grinding function as seen in birds such as ostriches (Wings and Sander 2007).

Finally, what could be more exciting than studying dinosaur coprolites or fossilized feces. Coprolites have been found at many sites and from a broad range of extinct species. Two interesting examples of the value of such finds to understanding dinosaur digestive function:

• A large coprolite discovered in Canada most likely came from the well-known Tyrannosaurus rex (Chin et al. 1998). Its size is 44 x 13 x 16 cm and roughly half of its substance is composed of bone fragments, compatible with the assumption that T. rex was clearly a meat eater, either as a predator or scavenger or both.
• Another coprolite likely from a tyrannosaurid dinosaur was remarkable because its microscopic structure indicated the presence of a large amount of undigested muscle tissue (Chin et al. 2003). The authors of this report interpreted this to indicate rapid gastrointestinal transit time for this carnivorous dinosaur, with insufficient time for full digestion to occur.

References

• Chin K, et al. A king-sized theropod coprolite. Nature 1998;; 393: 680-682.
• Chin K, et al. Remarkable preservation of undigested muscle tissue within a Late Cretaceous tyrannosaurid coprolite from Alberta, Canada. Palaios 2003; 18: 286-94.
• Varricchio DJ. Gut contents from a Cretaceous Tyrannosaurid: Implications for theropod dinosaur digestive tracts. J Paleontology 2001; 75: 401-406.
• Wings O and Sander PM. No gastric mill in sauropod dinosaurs: New evidence from analysis of gastrolith mass and function in ostriches. Proc R Soc B 2007; 274: 635-640.
• Zheng X, et al. Exceptional dinosaur fossils reveal early origin of avian-style digestion. Sci Reports 2018; 8: 14217.

Last updated October 2021. Send comments to Richard.Bowen@colostate.edu