Australia: The Land Where Time Began

A biography of the Australian continent 

Dinosaurs - Digestive Trace

Gastroliths, gizzard stones, have been found in the rib cage of  a number of dinosaur groups, often in the form of piles of stones. In the absence of the geological conditions that could explain the presence of rounded stones many polished stones have been found in some dinosaur formations. The author¹ suggests that many, and possibly all dinosaurs used gastroliths to grind their food.

Among the theropod predators the digestive tracts tended to be relatively short and simple systems, as they had evolved to rapidly process the chunks of flesh that were easily digested. The flesh would have been bitten off by, as the author¹ suggests, a simple scissors action of the jaws that contained serrated teeth, then bolted it in chunks as crocodilians do, as they had no teeth that had specialised for the crushing or grinding of their food, especially bone. Undigested bone is often found in large amounts in the coprolites that are believed to have been produced by large theropods, indicating that the food had passed rapidly along the digestive tract.

Many gastroliths have also been found in association with some theropods that were herbivores, presumably to help break down the plant material. As with herbivorous birds, most of the sauropods weren't adapted to chew their plant food. The gizzard was the site were the food was broken down physically which the author¹  suggests may have been used to stir up the food. Long, complex digestive tracts, housed in long rib cages, were required by the sauropods to ferment and breakdown chemically the leaves and twigs in their food. The titanosaurs took this system to the extreme with their broad bellies.

Some prosauropods and therizinosaurs appear to have had cheeks. The author¹ suggests that if they did indeed have cheeks it would have allowed them to pulp food before swallowing, the system that was fully exploited by the ornithischians that exploited this system fully. Food that had been cropped with their beak could be crushed by the dental batteries. According to this suggestion any food that lodged between the cheek and the teeth could be held in the cheek pouches until the tongue moved it back between the teeth by the tongue allowing it to be either chewed more or swallowed. The hadrosaurs, that had abdomens of moderate size, made most use of this system, evolving dental complexes further than any other dinosaur. The tooth complexes in some of the ornithischians had tooth complexes that were relatively weak, instead using massive digestive tracts and very large bellies to do the ferment and digest food. An enlargement of the intestines behind the pelvis of pachycephalosaurs was accommodated by the broadening of the tail base. Dense bundles of gastroliths were used  by a few ornithischians to supplement the processing of plant material.

The known evidence does not support the notion that herbivorous dinosaurs may have developed a ruminant-like system that involved cud-chewing. This system only works with medium-sized animals, so would  not be suitable for the large dinosaurs.

Sources & Further reading

1. Paul, Gregory S., 2010, The Princeton Field Guide to Dinosaurs, Princeton University Press.

Dinosaurs