The fossil record offers a complex puzzle when attempting to determine the diets of extinct creatures, particularly dinosaurs. Paleontologists often encounter feeding behaviors that do not fit neatly into the simple categories of meat-eater or plant-eater. The search for the largest dinosaur to have consumed both animals and vegetation leads to a massive animal whose identity remained a mystery for nearly fifty years.
Determining Dinosaur Diet
Paleontologists rely on a variety of indirect and direct evidence to reconstruct the feeding habits of dinosaurs. The most common clues are found in the anatomy of the skull, particularly the teeth and jaw structure. Carnivorous dinosaurs typically possess sharp, serrated teeth for slicing flesh, while herbivores have broad, blunt, or peg-like teeth designed for grinding plant matter. Jaw mechanics also indicate diet, as the powerful, simple up-and-down bite of a predator differs from the side-to-side grinding motion of a grazer.
Beyond skeletal features, direct evidence, though rare, is the most definitive. Fossilized stomach contents, or gut regions, can sometimes preserve the remains of a dinosaur’s last meal, such as fish scales or fragments of undigested plants. Another form of direct evidence comes from coprolites, or fossilized dung, which can reveal the presence of seeds, bones, or other organic material. Furthermore, the presence of gastroliths, or swallowed stones, suggests a diet containing fibrous plant material that required mechanical breakdown in a muscular gizzard.
The Largest Known Omnivore
The largest known omnivorous dinosaur is Deinocheirus mirificus, an ostrich-like creature from the Late Cretaceous period. Its name, meaning “terrible hand,” was inspired by the initial discovery in 1965 of only its massive forelimbs, which measured about eight feet long and ended in three-fingered claws. This finding led researchers to initially hypothesize it was a formidable predator.
However, subsequent discoveries in the early 2000s, including two more complete specimens from Mongolia’s Nemegt Formation, unveiled the animal’s true form. This dinosaur was part of the Ornithomimosaur group, but its size was exceptional, reaching approximately 36 feet in length. Weighing an estimated 6.5 tons, Deinocheirus was a bulky animal with a large, humped back formed by tall neural spines along its vertebrae. This scale establishes it as the largest dinosaur known to have pursued a mixed diet.
Physical Evidence of a Mixed Diet
Deinocheirus’s omnivory was confirmed by a combination of its anatomy and preserved internal contents. Its elongated skull was toothless and ended in a broad, flattened beak, similar to that of a duck-billed dinosaur. This shovel-like jaw structure suggests an adaptation for foraging or sifting through soft sediment and vegetation.
The most compelling proof came from the abdominal cavity of one specimen. Paleontologists recovered more than 1,400 gastroliths, or stomach stones, within the region where the gizzard would have been located. These stones were used to grind up plant matter, confirming the consumption of fibrous vegetation. Among the gastroliths, researchers also found fish remains, including scales and vertebrae, providing direct evidence that the dinosaur consumed aquatic life. This combination definitively proved its omnivorous diet and likely semi-aquatic lifestyle.
Other Large Dinosaurs with Omnivorous Tendencies
While Deinocheirus holds the record for size, other large theropods displayed omnivorous tendencies. The Ornithomimosaur group, to which Deinocheirus belongs, includes smaller members like Gallimimus and Struthiomimus. These dinosaurs likely consumed a mixed diet of plants, eggs, insects, and small vertebrates. Their toothless beaks and overall body plan are indicative of generalist feeders.
Another notable example is the Oviraptorosaur group, which includes the large Gigantoraptor. Though its diet is still debated, its size was substantial, reaching up to 26 feet long, and its relatives are known or suspected omnivores. These instances highlight that classifying a dinosaur’s diet often involves navigating a spectrum of ecological niches. None approached the weight and length of Deinocheirus mirificus.