Huge 6,000-pound crocodile terrorized prehistoric seas Suffice it to say, if this beast was in the water, you'd want to be out of the water. What is this creature? It is the largest sea-dwelling crocodile that has ever been discovered, growing to over 30 feet long and weighing three tons. That's right. It weighed more than 6,000 pounds. Fortunately for humans, the enormous crocodile, discovered in the Tunisian deserts, was the terror of Jurassic and Cretaceous seas, National Geographic reports. It's been dubbed Machimosaurus rex by paleontologist Federico Fanti, of the University of Bologna in Italy, and colleagues, who discovered the big beast. The dig was supported by the National Geographic Society. The findings were described in the journal Cretaceous Research. This giant croc had a skull that was immense, some five feet in length. While the remains are a bit fragmentary, there was enough left behind in the 120-million-year-old rock that the scientists were able to identify the reptile as the largest known member of an unusual crocodile lineage. These crocs spent nearly their whole lives at sea. Stephen Brusatte, a paleontologist with the University of Edinburgh, wasn't involved with the study, but he noted that this is a fascinating discovery that comes from a part of the world that hasn't really hasn't been explored much for fossils. This croc would have been one of the top predators in it's world, and at that time, an ocean separated Africa from Europe, News.com.au reports. "This is an incredibly big crocodile," Fanti said. "It is twice as big as a present-day marine crocodile. The skull itself is as big as I am." At the time when the great beast lived, Tunisia was a lagoon that was teeming with huge fish and turtles, everything a hungry Machimosaurus rex could want. "He was so big and so powerful that it was absolutely at the top of the food chain." It's not just size that makes this critter significant. What's also significant is what it tells paleontologists about a mass extinction that many believe happened as the Jurassic shifted into the Cretaceous period around 150 million years ago. This discovery suggests the extinction event wasn't as widespread as some paleontologists thought. Machimosaurus is in a group of crocodilians known as the teleosaurids, and it had been thought that this group died out as part of a mass extinction 145 million years ago, National Geographic reports. There was more than one species of machimosaurus, it should be noted. The discovery of Machimosaurus rex in later rocks dated to the Cretaceous suggests that if a mass extinction occurred, it didn't wipe out creatures planet-wide. "The new find adds to growing evidence that a lot of marine reptiles made it across the boundary and through the supposed extinction," Brusatte told National Geographic. Instead of happening rapidly, the extinction may have been a more drawn-out transition. "In our interpretation, the end-Jurassic event was global in its effects but was mostly likely a complex sequence of local biological crises that are still poorly documented." The remains of other species of Machimosaurus have been found in Europe and North America, HuffPost Science reports. The fossils of these species were analyzed, and seem to suggest that the marine crocodiles had been affected by a mass extinction that closed out the Jurassic Period. But the discovery of M. rex changed that by showing that the species lived and thrived for another 25 million years, well into the Cretaceous. "Therefore, this discovery sheds new light on the hypothesized mass extinction event at the end of the Jurassic--a biological crisis currently much less understood than the famous extinction at the end of the Cretaceous that wiped out the dinosaurs," Fanti said. Brusatte said it's likely Machimosaurus rex was an ambush predator, lurking in shallow water where it grabbed turtles, fish, and the occasional land animal. While it's the largest saltwater crocodile that we know of, at least two prehistoric freshwater crocodiles were even bigger than this big beast. Sarcosuchus imperator also known as the "SuperCroc," had a skull that was six feet long, National Geographic reports. Discovered by paleontologist and National Geographic Explorer-in-Residence Paul Sereno, this enormous crocodile, whose Latin name means "flesh crocodile emperor," lived about 110 million years ago, in what is now sub-Saharan Africa. Rivers coursed through this area during the time when this huge critter walked the earth. It likely feasted on fish and any other critters who were in the wrong place at the wrong time. Based on what he and his team found, Sereno estimated SuperCroc weighed up to ten tons and measured up to 40 feet in length. Also funded by the National Geographic Society, the researchers pored through the sands of Gadoufaoua, a fossil graveyard in Niger. They unearthed scores of Sarcosuchus remains, including vertebrae, armor plates, limb bones, jaws, and the aforementioned skull, which was nearly complete. Then there was the "terrible crocodile" Deinosuchus, which terrorized the marshes and swamps of North America's Western Interior Seaway between 80- and 73 million years ago, Smithsonian.com reports. A Cretaceous cousin of modern alligators, Deinosuchus fossils have been found from Mexico to Montana, and on the east coast in states such as North Carolina and Georgia. Paleontologists have unearthed bony armor, vertebrae, and the teeth of Deinosuchus, and pieces of jaw and partial skeletons have been found in places like Texas and Utah. This evidence indicates that this alligatoroid was also huge, growing over 30 feet in length and perhaps up to 40 feet in the largest individuals. It would be another five million years before Tyrannosaurus rex made it on the scene, and while smaller tyrannosaurs like Daspletosaurus and Teratophoneus were prowling around, they weren't nearly as big or bulky as their famous relative. This means that in their heyday, adult Deinosuchus were among the largest predators in their ecosystems. As adults, these critters were very likely heavier and longer than the largest dinosaurs around at the time, Smithsonian.com notes. With its massive skull and teeth adapted for piercing and crushing, this huge alligatoroid had the ability to take down hadrosaurs and other unlucky dinosaurs who weren't paying attention, or strayed too close to the wrong part of the water's edge. And there is plenty of evidence that Deinosuchus did, in fact, eat dinosaurs. Hadrosaur bones have been unearthed that tell the tale. What we don't know is if this big beast did take down dinosaurs. Sure, those hadrosaur bones had tooth marks in them, but there's not enough evidence to show that they did anything more than scavenge. So the jury's out on that one. It's enough to make a dinosaur nervous. Click to expand... lol If even dinosaurs may have fallen prey to this thing, that officially makes it the most feared creature to have ever lived. An enormous creature like this one needs its own movie.