A crocodile is any species belonging to the family Crocodylidae (sometimes classified instead as the subfamily Crocodylinae). The term can also be used more loosely to include allextant members of the order Crocodilia: i.e. the true crocodiles, the alligators and caimans (family Alligatoridae) and the gharials (family Gavialidae), as well as the Crocodylomorpha, which includeprehistoric crocodile relatives and ancestors.
Crocodiles are very fast over short distances, even out of water. Since they feed by grabbing and holding onto their prey, they have evolved sharpteeth for tearing and holding onto flesh, and powerful muscles to close the jaws and hold them shut. These jaws can bite down with immense force, by far the strongest bite of any animal. The jaws areopened, however, by a very weak set of muscles.
Crocodiles are among the more biologically complex reptiles despite their prehistoric look. Unlike other reptiles, a crocodile has a cerebral cortex, afour-chambered heart, and the functional equivalent of a diaphragm, by incorporating muscles used for aquatic locomotion into respiration. Its external morphology, on the other hand, is a sign of itsaquatic and predatory lifestyle.
Sharks are a group of fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused tothe head. Modern sharks are classified within the clade Selachimorpha (or Selachii), and are the sister group to the rays. However, the term "shark" has also been used for extinct members of thesubclass Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus. Under this broader definition, the earliest known sharks date from more than 420 million years ago.
Digestioncan take a long time. The food moves from the mouth to a J-shaped stomach, where it is stored and initial digestion occurs.
One of the biggest differences between the digestive systems of sharks and...