9 Animals That Ate Dinosaurs

Illustration representing Tylosaurus in sea

It's hard to imagine a dinosaur being eaten by anything but a bigger, hungrier dinosaur: after all, weren't these the apex predators of the Mesozoic Era, routinely feasting on mammals, birds, reptiles and fish? The fact is, though, that meat-eating and plant-eating dinosaurs alike often found themselves on the wrong end of the food chain, either overmatched by comparably sized vertebrates or gobbled up as hatchlings or juveniles by opportunistic predators. Below you'll discover nine animals that, according to incontestable fossil or circumstantial evidence, ate various dinosaurs for breakfast, lunch and dinner. 

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Wikimedia Commons

A 35-foot-long prehistoric crocodile of late Cretaceous North America, Deinosuchus had plenty of opportunities to munch on any plant-eating dinosaurs that ventured too close to the river's edge. Paleontologists have discovered scattered hadrosaur bones bearing Deinosuchus tooth marks, though it's unclear whether these duck-billed dinosaurs succumbed to ambush attacks or were merely scavenged after their death, and there is also evidence of Deinosuchus attacks on full-grown tyrannosaurs like Appalachiosaurus and Albertosaurus. If Deinosuchus did in fact hunt and eat dinosaurs, it probably did so in the manner of modern crocodiles, dragging its unfortunate victims into the water and submerging them until they drowned.

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The skull of Repenomamus. Wikimedia Commons

There were two species of the early Cretaceous mammal Repenomamus, R. robustus and R. giganticus, which may give you a misleading impression of this animal's size: full-grown adults weighed only 25 or 30 pounds soaking wet. That was, however, very impressive by Mesozoic mammal standards, and helps explain how one specimen of Repenomamus was found to harbor the fossilized remains of a juvenile Psittacosaurus, a genus of horned, frilled dinosaur distantly ancestral to Triceratops. The trouble is that we can't tell if this particular Repenomamus actively hunted and killed its wee prey, or scavenged it after it had died of natural causes.

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Wikimedia Commons

One of the biggest pterosaurs that ever lived, Quetzalcoatlus had a wingspan of 35 feet and may have weighed as much as 500 or 600 pounds—proportions that have prompted some experts to wonder if it was capable of active flight. If Quetzalcoatlus was, in fact, a terrestrial carnivore, stomping across the North American underbrush on its two hind feet, then dinosaurs would certainly have figured in its diet—not a full-grown Ankylosaurus, of course, but more easily digested juveniles and hatchlings. (Of course, if Quetzalcoatlus could fly, there was nothing preventing it from swooping down from the sky and carrying off a baby titanosaur!)

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Alain Beneteau

It's like an episode of Mesozoic CSI: in 2005, an amateur fossil hunter in Kansas discovered the fossilized tail bones of a duck-billed dinosaur, bearing what appeared to be the tooth marks of a shark. Suspicion initially fell on the late Cretaceous Squalicorax, but the match wasn't quite right; serious detective work then identified the more likely culprit, Cretoxyrhina, aka the Ginsu Shark. Clearly, this dinosaur wasn't out for an afternoon swim when it as suddenly attacked, but had already drowned and was opportunistically filleted by its hungry nemesis. (In case you were wondering, tens of millions of years ago the American west was covered by a shallow body of water, the Western Interior Sea, well-stocked with sharks and marine reptiles.)

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Wikimedia Commons

By the standards of the truly monstrous Titanoboa, the prehistoric snake Sanajeh wasn't very impressive, barely 10 feet long and as thick as a sapling. But this reptile did have a unique feeding strategy, seeking out the nesting sites of titanosaur dinosaurs and either devouring the eggs outright or gobbling up the unfortunate hatchlings as they emerged into daylight. (Unlike modern snakes, Sanajeh couldn't open its mouth to an extremely wide angle, so any dinosaur bigger than a hatchling would have been off limits.) How do we know all this? Well, a Sanajeh specimen was recently discovered in India wrapped around a preserved titanosaur egg, with the fossil of a 20-inch-long titanosaur hatchling nearby!

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Didelphodon. Wikimedia Commons

The case for the dinosaur-eating proclivities of Didelphodon—a 10-pound mammal of late Cretaceous North America—is circumstantial at best, but entire scholarly papers in reputable paleontology journals have been based on less. Studies of its skull and jaws have shown that Didelphodon possessed the strongest bite of any known Mesozoic mammal, almost on a par with the "bone-crushing" dogs of the later Cenozoic Era and exceeding that of the modern hyena; the logical conclusion is that small vertebrates, including newly hatched dinosaurs, were a major component of its diet. (Technically, Didelphodon is classified as a metatherian mammal, meaning that it's more closely related to marsupials than placentals.)

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Nobu Tamura

In the climactic scene of Jurassic World, a humongous Mosasaurus drags Indominus rex to a watery grave. Granted that even the biggest Mosasaurus specimens were about 10 times smaller than the monster of Jurassic World, and that Indominus rex is a completely made-up dinosaur, this may not be far from the mark: there's every reason to believe that mosasaurs (the family of marine reptiles that dominated the earth's oceans during the late Cretaceous period) attacked dinosaurs that accidentally fell in the water during storms, floods or migrations. The best piece of circumstantial evidence: the prehistoric shark Cretoxyrhina (see slide #5), a marine contemporary of the mosasaurs, also had dinosaurs on its dinner menu.

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Wikimedia Commons

Dinosaurs, and other vertebrate animals, don't necessarily have to be consumed from the outside; they can also eaten away from within. A recent analysis of the coprolites (fossilized poop) of a unidentified genus of meat-eating dinosaur shows that this this theropod's intestines were infested with nematodes, trematodes and, for all we know, hundred-foot-long tapeworms. There's also good circumstantial evidence for Mesozoic parasites: modern birds and crocodiles both descend from the same family of reptiles (the archosaurs) as dinosaurs, and their twisty guts are hardly whistle-clean. What we can't say for sure is whether these tyrannosaur-sized tapeworms made their hosts ill, or served some kind of symbiotic function.

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Bone-Boring Beetles

Wikimedia Commons

Like all animals, dinosaurs decomposed after their deaths—a process accomplished by bacteria, worms, and (in the case of one fossil specimen of the duck-billed dinosaur Nemegtomaia) bone-boring beetles. Apparently, this unfortunate plant-muncher wound up half-buried in the muck after it died of natural causes, leaving the left side of its body exposed to famished beetles of the Dermestidae family. (Here's a fun fact you can tell at your next dinner party: natural history museums regularly maintain their dinosaur bones by exposing them to dermestid beetles, and these bugs are often set loose on human skulls to prepare them for study or display.)