The 10 Deadliest Dinosaurs - The Scariest Dinosaurs that Ever Lived

We'll never know if T. Rex was particularly fiercer or scarier than other, less popular tyrannosaurs like Albertosaurus or Alioramus--or even whether it hunted live prey or feasted on already-dead carcasses. Whatever the case, there's no question that Rex was a fully functional killing machine when circumstances demanded, with its five- to seven-ton bulk and huge head studded with numerous, sharp teeth. (You have to grant, though, that its tiny arms lent it a slightly comic appearance.) Read more about T. Rex

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 two tons. On Utahraptor, the characteristic, single curved claws of the raptor family attained Friday the 13th sizes, kind of 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 perhaps faster). Read more about Utahraptor

Jeholopterus is a more controversial inclusion than other carnivores on this list--not because it was a pterosaur rather than a true dinosaur, but because paleontologists disagree about its basic anatomy. The researcher who "diagnosed" Jeholopterus (based on a single, squashed, but near-intact fossil) concluded that it sported sharp fangs, and speculation ensued that this mid-sized, flying reptile sucked the blood of ponderous sauropods like a Jurassic vampire bat. Maybe--but then again, maybe not. Read more about Jeholopterus

Any carnivore named after Kronos--the god of Greek myth who ate his own children--must have been one bad character. Simply put, Kronosaurus was much, much bigger than a modern great white shark, and it had much, much bigger (and scarier) teeth. This aquatic reptile seems to have eaten anything unlucky enough to cross its path, ranging from fish to squids to other, smaller pliosaurs and plesiosaurs--and perhaps even the occasional dinosaur that ventured too close to the water's edge. Read more about Kronosaurus

Deadliness isn't simply a matter of size or armament. Troodon weighed only about 150 pounds (about as much as a full-grown human male), and it didn't have particularly sharp or scary-looking teeth. What set it apart was its relatively big brain, compared to other carnivorous dinosaurs of the late Cretaceous period, and its presumed ability to hunt in packs at night (the giveaway was its large eyes). The bottom line: four or five alert Troodon might have been equivalent in danger to one full-grown T. Rex. Read more about Troodon

It can be, well, dangerous to speculate about how many individuals existed of a given genus, based solely on fossil remains. But if we make that leap, then Allosaurus was a deadlier predator than T. Rex--numerous fossils of this fierce, strong-jawed, three-ton carnivore have been found across the western U.S. As deadly as it was, though, Allosaurus wasn't very smart--many adults perished at a single quarry in Utah, becoming mired in the deep muck as they salivated over already-trapped herbivores. Read more about Allosaurus

Better known as the SuperCroc, Sarcosuchus was about twice as long and 10 times as heavy as the largest crocodiles living today--making it the crocodilian equivalent of the aquatic reptile Kronosaurus, which was 10 times the weight of a modern great white shark. In fact, this Cretaceous crocodile may have been gigantic enough to lunge suddenly out of a lake or river, snag a full-grown sauropod by its long neck, and drag it kicking and screaming back into the water for a quick lunch. Read more about Sarcosuchus

If this ichthyosaur sound vaguely familiar, that's because it was named after Excalibur, King Arthur's mythical sword. Like a modern-day swordfish--only a lot, lot bigger--Excalibosaurus seems to have used its long, pointed, tooth-studded snout to spear big fish for dinner and keep others of its kind at bay. Weirdly, the top half of Excalibosaurus' jaw protruded a full foot beyond its lower jaw--which might (if they hadn't been so terrified) have prompted some cruel teasing from its fellow aquatic reptiles. Read more about Excalibosaurus

In Cretaceous times, the dinosaurs of South America were bigger and fiercer than their counterparts around the globe. Exhibit A is Giganotosaurus, an eight-ton, three-fingered, romping, stomping carnivore whose remains have been found in close proximity to those of slaughtered Argentinosaurus, one of the biggest herbivores ever to walk the earth. The inescapable conclusion: Giganotosaurus was one of the few theropods capable of taking down (and eating up) a full-grown titanosaur adult. Read more about Giganotosaurus

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 has been entirely unearned. The discovery of ancient Majungatholus bones bearing ancient Majungatholus tooth marks is a good indication that these one-ton theropods preyed on others of their kind, though they probably spent most of their time terrifying the smaller, quivering herbivores of late Cretaceous Africa. Read more about Majungatholus