Out of all the dinosaurs discovered so far, only 1-2% could consume plant and animal matter. These dinosaurs were omnivores who could consume protein from the flesh of other creatures while also breaking down and digesting the complex compounds found in vegetation.
Interestingly most of these omnivorous dinosaurs were agile, medium-sized creatures, which has led to the belief that they were opportunistic feeders. This meant they would have a greater chance of surviving harsh periods of food scarcity and didn’t need to consume too much to sustain themselves.
Some well-known dinosaurs believed to be omnivores belonged to a select few families like Ornithomimosaurs, Troodontids, and Oviraptorosaurs. Common examples include Gallimimus, Ornithomimus, and Oviraptor.
There are a few particular characteristics that paleontologists use to determine whether or not a dinosaur was omnivorous:
While most omnivorous dinosaurs were not very large, Deinocheirus mirificus was the exception. An ornithomimosaur like Gallimimus and Struthiomimus, Deinocheirus was the biggest of the bunch, reaching up to 36 feet in length and weighing over six tons. It seems to have lived close to water, most likely feeding on herbs that grew in aquatic environments and fish.
Fruitadens haagarorum, a heterodontosaur, is widely believed to be the smallest dinosaur to be an omnivore. It was 26 to 30 inches long and weighed between 1.1 and 1.7 lbs.
These dinosaurs probably consumed a wide variety of foodstuffs, including plant material like fruits, seeds, and vegetables, as well as animals like small mammals, fish, insects like dragonflies, crabs, and even other dinosaurs. They may have even consumed carrion after a larger predator had finished their meal, like modern-day jackals.