Crocodilians are a group of reptiles that include crocodiles, alligators, caimans, and gharials. They are characterized by their elongated bodies, powerful jaws, and semi-aquatic lifestyle, often inhabiting freshwater environments like rivers and swamps. Crocodilians are known for their strong parental care and are considered living fossils, as they have existed for millions of years with relatively little evolutionary change. They play a crucial role in their ecosystems as both predators and prey.