Sarcosuchus

     Nicknamed the SuperCroc, the primitive Sarcosuchus imperator (pronounced SAR-koh-SOO-kiss IM-peh-RAH-tor and meaning “flesh crocodile emperor” from the early Cretaceous of Africa is one of the main giant crocodile-like reptiles that ever lived. It was almost twice as long as the largest modern crocodile, and weighed up to 10 times as much.
Until recently, all that was known of the species was a few fossilized teeth and armor plates, which were exposed in the Sahara Desert by the French paleontologist Albert-Félix de Lapparent in the 1940s or 1950s. However, in 1997 and 2000, Paul Sereno discovered a half a dozen new specimens, counting one with about half the skeleton intact, and most of the spine. All of the other giant crocodiles are recognized only from a few partial skulls, so which is actually the biggest is an open question.
   When fully mature, the SuperCroc was as extended as a city bus (11–12 m, or 37–40 ft), and weighed up to 8,000 kg (8.8 short tons), as much as the major known terrestrial carnivore, the dinosaur Giganotosaurus.    
     The saltwater crocodile is the largest modern species, and only reaches half that length (6.3 m, or 20.7 ft, is the longest long-established individual), and a small fraction of the weight (1,000 kg, or 1.1 tons).The largest SuperCroc was the oldest, because it kept rising through its entire 50–60 year lifespan. Modern crocodiles grow at a rapid rate, attainment their adult size in about a decade, and then grow more slowly afterwards. The SuperCroc probably grew at the same rate, but kept growing for up to 40 years before reaching its full adult size.
    Its jaws alone were as big as a human adult (1.8 m, or 6 ft). The upper jaw overlaps the lower jaw, creating an overbite, and together was narrow. The snout composes about 75 percent of the skull's length.
It’s contained 132 thick teeth (Larsson said they were like "railroad spikes"). The teeth are conical and designed for grabbing and holding, instead of being narrow and designed for slashing (like the teeth of most land-dwelling carnivores). It could probably exert a force of 18,000 lbf (80 kN) with its jaw, making very improbable that prey could escape.

   It had a row of overlapping bony plates, or scutes, running down its back, the main of which were 1 m (3 ft) long. The scutes served as armor and may have helped support its great mass, but also restricted its flexibility.Like a gharial, the SuperCroc had an air cell in a bony projection at the tip of its snout (a bulla), which might have augmented its sense of smell, or been used for a variety of vocalizations.
Like modern crocodiles, the SuperCroc could almost certainly make a wide range of vocalizations, from grunts and squeaks to hisses, growls, barks, bellows, and roars. The SuperCrocs may have used these sounds to stake out territory, to attract mates, and to converse with their progeny.
Like modern crocodiles, the SuperCroc's eye sockets rotate upwards, so it probably spent most of its time with the bulk of its body submerged, watching the shore for prey.
It seems likely that it ate the large fish and turtles of the Cretaceous. But the overhanging jaw and stout teeth are designed for grabbing and crushing, so its main prey was probably large animals and smaller dinosaurs, which it ambushed, dragged into the water, drowned, and then tore apart.
It may have even come into disagreement with the Suchomimus, an 11 m (36 ft) fish-eating dinosaur with a strangely crocodilian jaw, whose fossils were establish in the same rock formation as the SuperCroc. According to Sereno, "because the ancient animal was so large, it could easily grip huge dinosaurs, including the massive long-necked, small-headed sauropods that were common in that African region".
Other crocodilian biologists are cynical of the animal's "giant killing" capabilities. The long, thin snout of the SuperCroc is very alike to the thin snouts of the gharial, false gharial, and the slender-snouted crocodile, all of which are nearly elite fish-eaters, and incapable of tackling large prey. This can be contrasted to both the modern Nile crocodile and the died out Deinosuchus which have very broad, heavy skulls, suitable for dealing with large prey. This, coupled with the abundance of large, lobe-finned fish in its environment, leads many to propose that, far from being a dinosaur killer, SuperCroc was simply a large piscivore, a scaled-up version of the new gharial.
    However, while the snout of the juvenile SuperCroc powerfully resembles modern narrow-snouted crocodiles in width, it expands radically in mature SuperCrocs. While still considerably narrower than the snout of a Nile crocodile, in grown-up SuperCrocs it is also much wider than the snouts of crocodylians like the gharial. In addition, the teeth do not interlock like those of the elite fish-eaters, which suggests that like the Nile crocodile it may have complemented a first and foremost piscean diet with terrestrial animals, at least upon adulthood.
On the other hand, the lobe-finned fish that shared the waters with Sarcosuchus were often in surplus of 6 feet (1.8 m) long and 200 lb (90 kg) in weight, raising the option those adoptions which seem to indicate large or moderate-sized terrestrial prey may instead be adaptations to dealing with very large fish (many species of which possessed a layer of bony scales, called osteoderms, for protection).