Crocodylia
Introduction
Crocodylia (or Crocodylomorpha) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodiles. They first appeared 95 million years ago in the Late Cretaceous period and are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria. Members of the order's total group, the clade Pseudosuchia, appeared about 250 million years ago in the Early Triassic period and diversified during the Mesozoic Era. The order Crocodylia includes the true crocodiles (family Crocodylidae), the alligators and caimans (family Alligatoridae), and the gharials and false gharials (family Gavialidae). Although the term 'crocodiles' is sometimes used to refer to all of these, crocodilians is a less ambiguous vernacular term for members of this group.
Evolution
Crocodylians have evolved a variety of adaptations to an amphibious lifestyle. They have a streamlined body that enables them to swim swiftly; they also tuck their feet to their sides while swimming, which makes them faster by decreasing water resistance. They have webbed feet which, though not used to propel them through the water, allow them to make fast turns and sudden moves in the water or initiate swimming. Webbed feet are an advantage in shallower water, where the animals sometimes move around by walking.
Anatomy and Morphology
Crocodylians are more closely related to birds and dinosaurs than to most animals classified as reptiles, the three being included in the group Archosauria ('ruling reptiles'). The most obvious external differences are visible in the head, with crocodiles having narrower and longer heads, with a more V-shaped than a U-shaped snout compared to alligators and caimans. Another obvious trait is that the upper and lower jaws of the crocodiles are the same width, and the teeth in the lower jaw fall along the edge or outside the upper jaw when the mouth is closed; therefore, all teeth are visible, unlike an alligator, which possesses in the upper jaw small depressions into which the lower teeth fit.
Behavior and Ecology
Crocodylians are typically solitary and territorial creatures, though they are known to tolerate the presence of other individuals during feeding and basking times. They are also known to engage in various social behaviors, including complex courtship and mating rituals, nest building, and parental care. They are also known for their sophisticated hunting techniques, which often involve cooperative efforts between multiple individuals.
Conservation
Many species of crocodylians are at the risk of extinction, mainly due to habitat destruction and hunting. Conservation efforts include captive breeding, setting up protected areas, and educating the public about these animals. Some species have shown a good recovery after the implementation of these conservation efforts.