10 Deadliest Dinosaurs of the Mesozoic Era

An 1897 painting of "Laelaps" (now Dryptosaurus)

Charles Robert Knight/Wikimedia Commons/Public Domain

As a general rule, you wouldn't want to cross paths with any of the dinosaurs that lived during the Mesozoic Era—but the fact remains that some species were much, much more dangerous than others. On the following slides, you'll discover 10 tyrannosaurs, raptors, and other kinds of dinosaurs that could turn you into lunch (or a flattened, quivering pile of bones and internal organs) faster than you can say "Jurassic World."

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Giganotosaurus dinosaur skeleton on textured background.

 Harm Plat/Stocktrek Images/Getty Images

During the Cretaceous period, the dinosaurs of South America tended to be bigger and fiercer than their counterparts elsewhere on the globe. Exhibit A is Giganotosaurus, an eight- to 10-ton, three-fingered predator whose remains have been found in close proximity to those of Argentinosaurus, one of the biggest dinosaurs ever to walk the earth. The inescapable conclusion: Giganotosaurus was one of the few theropods capable of taking down a full-grown titanosaur adult (or, at least, a more manageable juvenile). 

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Side profile of two utahraptors fighting

Deinonychus and Velociraptor get all the press, but for sheer killing ability, no raptor was more dangerous that Utahraptor, adult specimens of which weighed almost a ton (compared to 200 pounds, top, for an exceptionally big Deinonychus). With Utahraptor, the characteristic, single curved claws of the raptor family attained Friday the 13th-worthy sizes, a bit like the difference between a medieval broadsword and a Swiss army knife. Weirdly, this giant-sized raptor lived 50 million years before its more famous descendants, which were considerably smaller (but a lot faster).

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Tyrannosaurus Rex

Tyrannosaurus Rex


Dave and Les Jacobs / Getty Images

We'll never know if Tyrannosaurus Rex was particularly fiercer or scarier than other, less- popular tyrannosaurs like Albertosaurus or Alioramus—or even whether it hunted live prey or spent most of its time feasting on already-dead carcasses. Whatever the case, there's no question that T. Rex was a fully functional killing machine when circumstances demanded, considering its five- to eight-ton bulk, sharp eyesight, and huge head studded with numerous, sharp teeth. (You have to admit, though, that its tiny arms lent it a slightly comical appearance.)

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The spiked tail of a Stegosaurus
Eduard Solà/Wikimedia Commons/CC BY-SA 3.0

You might not expect to encounter a small-headed, small-brained plant eater like Stegosaurus on a list of the world's deadliest dinosaurs—but focus your attention on the other side of this herbivore's body, and you'll see a dangerously spiked tail that could easily bash in the skull of a hungry Allosaurus (see slide #9 below). This thagomizer (so named after a famous Far Side cartoon) helped to compensate for Stegosaurus' lack of intelligence and speed; one can easily imagine a cornered adult flopping down on the ground and swinging its tail wildly in all directions.

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spinosaurus skeleton
Kabacchi/Wikimedia Commons/CC BY 2.0

In roughly the same weight class as Giganotosaurus and Tyrannosaurus Rex, the northern African Spinosaurus was blessed with an additional evolutionary advantage: it's the world's first identified swimming dinosaur. This ten-ton predator spent its days in and around rivers, pinning fish between its massive, crocodile-like jaws and occasionally surfacing like a shark to terrorize smaller, landbound dinosaurs. Spinosaurus may even have tangled occasionally with the comparably sized crocodile Sarcosuchus, aka the SuperCroc, surely one of the epic matchups of the middle Cretaceous period.

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Majungasaurus in a barren environment.

 Stocktrek Images/Getty Images

Majungasaurus, once known as Majungatholus, has been dubbed the cannibal dinosaur by the press, and even though this may be overstating the case, that doesn't mean this carnivore's reputation is entirely unearned. The discovery of ancient Majungasaurus bones bearing equally ancient Majungasaurus tooth marks is a good indication that these one-ton theropods preyed on others of their kind (certainly when they were very hungry, and possibly after they were already dead), though this predator spent most of its time terrifying the smaller, quivering plant-eating dinosaurs of late Cretaceous Africa.

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The tail club of Ankylosaurus
Domser/Wikimedia Commons/CC BY-SA 3.0

The armored dinosaur Ankylosaurus was a close relative of Stegosaurus (#5 above), and these dinosaurs repelled their enemies in ​a similar fashion. Whereas Stegosaurus had a spiked "thagomizer" on the end of its tail, Ankylosaurus was equipped with a massive, hundred-pound tail club, the late Cretaceous equivalent of a medieval mace. A well-aimed swing of this club could easily break the hind leg of a hungry Tyrannosaurus Rex, or even knock out a few of its teeth, though one imagines it may also have been employed in intra-species combat during mating season.

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allosaurus skull fossil
Oklahoma Museum of Natural History

It can be, well, deadly to speculate about how many individuals existed at any given time for any given dinosaur genus, based solely on the fossil evidence. But if we agree to make that imaginative leap, then Allosaurus was a far deadlier predator than the (much later) Tyrannosaurus Rex—numerous specimens of this fierce, strong-jawed, three-ton meat-eater have been discovered across the western U.S. As deadly as it was, though, Allosaurus wasn't very smart—for example, a group of adults perished in a single quarry in Utah, mired in deep muck as they salivated over already-trapped and struggling prey.

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The tail of Diplodocus
Lee Ruk from North Tonawanda/Wikimedia Commons/CC BY-SA 2.0

Surely, you must be thinking, Diplodocus doesn't belong on a list of the world's deadliest dinosaurs. Diplodocus, that gentle, long-necked, and invariably mispronounced plant-eater of the late Jurassic period? Well, the fact is that this 100-foot-long sauropod was equipped with a slender, 20-foot-long tail that (some paleontologists believe) it could crack like a whip, at hypersonic speeds, to keep predators like Allosaurus at bay. Of course, Diplodocus (not to mention the contemporaneous Brachiosaurus and Apatosaurus) could simply squish its enemies flat with a well-placed stomp of its hind foot, but that's a much less cinematic scenario.​

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Illustration of Troodon

Deadliness isn't always a simple matter of size or armament. The feathered dinosaur Troodon weighed only about 150 pounds soaking wet (about as much as a full-grown human), and it didn't have particularly sharp or scary-looking teeth. What set this theropod apart was its relatively big brain, at least compared to the other carnivorous dinosaurs of late Cretaceous North America, and its presumed ability to hunt in packs at night (the giveaway is its large eyes). The bottom line: four or five alert Troodon may well have been equivalent in danger to one hungry, full-grown T. Rex!