Crocodiles

Class: Reptilia
Clade: Sauropsida
Order: Crocodylia

Crocodiles are a large carnivorous aquatic reptiles noted for their frequent aggresive ambush predatory strategies in finding prey. 

An adult male saltwater crocodile is about 4.3–5.2 m long weighing 400–1,000 kg, though some can be even larger.

Crocodiles are quite different to other reptiles being  biologically more complex. Unlike other reptiles, crocodiles have a cerebral cortex, a four-chambered heart, and the functional equivalent of a diaphragm. 

800px-Saltwater_Crocodile_on_a_river_bank

A saltwater crocodile in the Northern Territory of Australia. image: wikipedia

Exotherms

But crocodiles, due to living in tropical warm areas, don't bother with spending metabolic energy maintaining their body temperature , they are essentially exothermic like all reptiles.

Evolution

The crocodylomorphs are the only pseudosuchians to have survived the Triassic–Jurassic extinction event, 201.3 million years ago. During the early Jurassic period, the dinosaurs became dominant on land, and the crocodylomorphs underwent major adaptive diversications to fill ecological niches vacated by recently extinguished groups.

Unfolding fossil evidence shows that Mesozoic crocodylomorphs had a much greater diversity of forms than modern crocodilians. Some became small fast-moving insectivores, others specialist fish-eaters, still others marine and terrestrial carnivores, and a few became herbivores.

source: http://en.wikipedia.org/wiki/Crocodilian

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