That's not a croc. This is a croc.
This is one of those animals you should be thankful are extinct. Sarchosuchus is a genus of prehistoric crocodilians related closely to modern crocodiles and alligators, although the modern crocodile is not descended from Sarchosuchus (think long-lost cousin -- the modern crocodilians and the Sarchosuchus both descend from a common ancestor). The Sarchosuchus was largely similar to modern-day crocodilians in body shape and ecological niche: It was a densely-muscled torpedo of a semiaquatic reptile, and it was a formidable predator that stood on the absolute top of the food chain.
The impressive feat about that is that it did so 110 million years ago, when dinosaurs were all the rage.
The Sarchosuchus was largely shaped like a modern crocodile: Vaguely resembling a very compact oversized lizard with gigantic jaws and thick armour plating instead of scales, it largely consisted of muscles, armour and teeth. Many, big teeth. Like the modern crocodile, its jaw musculature was specialized for snapping the creature's jaws shut with tremendous force -- that's why Steve Irwin can hold the mouth of a crocodile far stronger than himself shut; the same specialization that allows the animal to close its jaws with all that power prevents it from opening it easily if it's obstructed.
However, even if Steve Irwin metamorphosed into the Incredible fucking Hulk himself, he would be hard-pressed to pull such a trick on one of these things. The fossils found indicate that these animals easily grew to be 12 meters (40 feet) in length, and the estimated weight of such a monster is around 8 metric tons. Fossilized teeth and skull fragments have been found that indicate that even larger Sarchosuchi may have existed, possibly growing over 18 meters long. In comparison, the average Tyrannosaurus Rex was around 9-10 meters long, and weighed in at around 4 metric tons. We're talking about a crocodile the size of a bus!
To understand how the Sarchosuchus could grow so damn big, it's useful to know how reptile body growth works. Unlike mammals and birds that grow throughout childhood and then stop, all reptiles keep growing throughout their lives. Most modern-day reptiles grow at an extremely fast pace in the relatively short period from hatchling to young adult. When the reptile reaches sexual maturity, the most obvious change is that it develops secondary sex characteristics to clearly denote its sex -- examples include the large dorsal crests on a male iguana or water dragon, the femoral pores of male geckos or the horns of a male Jackson chameleon. Female reptiles typically look much more unimpressive than males, go sue Mother Nature for being sexist. The other, and in this context much more interesting, change is that the body's extremely fast metabolism of Vitamin D slows down. This causes the animal's growth to slow accordingly, making the animal grow very slowly throughout the rest of its life. Here's the kicker: The Sarchosuchus lacked this feature. Throughout its life, it kept growing at the rate it started the moment it left its egg. The armour plates of fossilized specimens indicate that the animals could grow 60-80 years old, perhaps even older (some modern crocodiles can live to be a hundred). One non-adult specimen had growth rings on its plates that indicated it was around 40 years old when it died. This puts them in contrast to the dinosaurs, which grew in amazingly fast bursts of growth in their youth, and didn't grow terribly old.
Apart from its monstrous size, the Sarchosuchus could be distinguished from a modern crocodile by the large bulla, a round protrusion at the end of its huge snout. It most likely used this as a smelling aid or perhaps to make sound (crocodilians being among the more vocal reptiles, discounting the singing geckos and their advanced vocal cords), but the exact function is unknown. It also had a much smaller brain-to-bodymass ratio than a modern crocodile -- the brain is one of the few parts of crocodiles that has actually evolved over the millions of years these walking fossils have existed.
Well, it's a safe bet that these guys and girls weren't exactly vegan. Just like a modern crocodile, the Sarchosuchus would lie in wait in a river somewhere, waiting for a tasty animal to come by. Its size, musculature and likely hunting style (the typical crocodilian ambush attack followed by a death roll) enabled it to take down even large dinosaurs with ease. For hors d'oeuvres, it most likely ate turtles and large prehistoric fish. Like a modern crocodile, it could achieve very high running speeds during short bursts, allowing it to go on land and hunt down anything trying to get away. Likely favourite food animals are the iguanodon and duckbill dinosaurs, animals that grew to a weight of several tons. Its jaws had a slight overbite, and appear to be specialized for crushing vertebrates. Its only likely competitor was Spinosaurus (popularized as the archvillain of Jurassic Park III), and even compared to that horror, Sarchosuchus had a distinct advantage: Being water-based, it essentially attacked out of nowhere. Its most likely feeding cycle was similar to modern crocodiles; it would probably catch a large piece of prey and then spend the next couple of months dozing, relaxing and digesting. Then it'd wake up one morning, feel hungry, and go kill something really big.
Sarchosuchus fossils have been found in Africa, near ancient riverbeds. A close, slightly smaller, relative, Dinosuchus, lived in what would eventually become the Americas. Only one species of the Sarchosuchus genus has been found, the Sarchosuchus imperator. The species name, imperator is latin for "Emperor", and is a play on the Tyrannosaurus Rex being King, but Sarchosuchus being Emperor.
Sarchosuchus lived in the Cretaceous age, which really was the Earth's golden age for very large reptilians and dinosaurs. Global warming allowed the vegetation of the time to grow absolutely gigantic, and very big plants allows for very big herbivores. Very big herbivores lead to the evolution of very big carnivores. The gigantic dinosaur carnivores are well-known, but the interesting thing about Sarchosuchus is that the exact same design still exists today (and existed long before Sarchosuchus), with only slight modifications. Modern crocodiles, as well as pre-Sarchosuchus crocodiles, are all variations of the same basic theme: Water-based reptilian marauders that attack by ambush and overpower prey by a combination of massive muscle power and nasty attack methods. The reason crocodilians have existed for so long is that the design works. Unfortunately, sitting on the top of the food chain is not really a good thing speaking in terms of evolution; an animal adapted to that role is much more susceptible to environmental changes -- bear in mind that anything that affects herbivores hits carnivores even harder; there are fewer carnivores than herbivores, and herbivores have an easier time adapting to changes than carnivores. There's only so many ways to develop hunting tactics if what you're hunting is grass. When the large herbivores disappeared, Sarchosuchus disappeared with them. Most of the evolutionary dead-ends of crocodilians were the extreme-sized Cretaceous ones (including Sarchosuchus on one extreme, and tiny two-inch insectivore crocodiles on the other), the medium-sized variants survived the dinosaurs and still exist today, with minimal adaptations over the ages. Except for the rare specialist (like the exclusively fish-eating gavial), modern crocodiles can eat pretty much anything that lives in their geographical area. Sarchosuchus was itself a specialist, specialized for killing very big things.