Alligator mississippiensis (Daudin, 1801) - American alligator skull (Newport Aquarium, Newport, Kentucky, USA).

The crocodilians have been around since the Triassic (early Mesozoic). Crocodilians include four groups: eusuchians (the only living group), mesosuchians (extinct), protosuchians (extinct), and sphenosuchians (extinct). Some fossil crocodilians reached such immense sizes that they preyed on dinosaurs. Another fossil group of reptiles, the phytosaurs (upload.wikimedia.org/wikipedia/commons/d/d2/Rutiodon_BW.jpg), closely resemble crocodilians, but are unrelated (phytosaurs are crurotarsan archosaurs).

All modern and fossil crocodilians have the same overall skeletal structure, although some fossils forms did depart somewhat from the stereotypical crocodile body plan (quadrupedal, dorso-ventrally compressed bodies, elongated skull & snout with eyes atop the head). So, the crocodilians are, in relative terms, evolutionarily conservative.

Living crocodilians are tropical to temperate, predatory semiaquatic reptiles, but fossil representatives include fully marine forms and inferred terrestrial forms.

Only two living crocodilians are native to America - the American alligator and the American crocodile. Both occur in the far-southeastern parts of the USA (Florida).

As are all crocodilians, the alligator is a predator (carnivore), although it also known to be a frugivore (fruit eater).

Note the pits/canals in the jaw bones - they are especially evident below the teeth of the mandible. These canals (neurovascular foramina) originally housed nerves that connected to integumentary sense organs (ISOs) in the skin. Such structures provide the animal with sensations “beyond-the-five senses”. ISOs are traditionally inferred to only function when at the air-water interface. However, ISOs along the flanks of crocodiles are essentially always below water. It's been shown that ISOs don't detect electric fields or magnetic fields. Vibration detection seems the most likely function of crocodilian ISOs, especially upon consideration of effective nocturnal hunting by most modern forms.