9781422275016

THE BEAST ITSELF

Alligators are creatures of habit. When one finds a good spot above the water level where it can bask in the sun, it will return to that spot day after day.

Prehistory to the Present Alligators, caimans, crocodiles, and gharials are jointly referred to as crocodilians. The croco- dilians are holdovers, survivors of that long-ago time known as the Age of Reptiles, a time when the dinosaurs were the ruling creatures on the Earth, dating from 265 million years ago to roughly 66 million years ago. The dinosaurs, the pterosaurs, and the crocodilians were known as Archesaurians, and even today, the crocodilians are referred to as saurians. At the end of the Triassic period, about 210 million years ago, a small, slim reptile appeared, which has been named Terrestrisuchus and is thought to be the direct ancestor of our mod- ern-day crocodilians. The terrestrisuchus, as its name implies, was primarily a land-dwelling reptile, running about on either two or four legs and feeding upon smaller lizards. The ankle joints of these early reptiles are similar to present-day crocodilians. It is one of the main links between them that these crea- tures could also either crawl slowly, bellies close to the ground, with the legs bent outward away from the body, or the legs could be straightened, lifting the body away from the ground and allow- ing the creature to run very rapidly for short distances. A creature known as Desmotosuchus also evolved that was very crocodilian in appear- ance and had evolutionary adaptations to a life in water, such as a vertically flattened tail for propulsion and a secondary palate that allowed them to seal their throat to prevent water from entering their lungs when they opened their mouths underwater. Both of these adaptations are present in today’s crocodilians. By the end of the Jurassic period, about 146 million years ago, the ancestors of present-day crocodilians had evolved, and

although the direct lineage from that era to the present is not precisely established, both form and function were. It was also during the Juras- sic period that the huge, single continent, known as Pangaea, split apart to form the continents we know today. This continental drift caused some forms of crocodilians to become separated. It also caused the great divergence, through iso- lation, into the many different species that we have today as each species evolved and adapted to the conditions in which each was found. There is great speculationabout the events that brought about the extinction of the dinosaurs. The one most favored is that a huge asteroid hit the Earth, sending up clouds of dust that envel- oped the planet, blocking the sun, which killed the plants that the dinosaurs lived on. A second theory, that the beginning of an ice age killed off the dinosaurs, is not generally accepted because most of the dinosaurs died at about the same time. Another theory is that neither of these things happened, but the cooling of the Earth

Turtles frequently climb up on an alligator or crocodile to bask in the sun, just as if they were on a log. This is risky because many of the crocodilians feed upon turtles.

Although this alligator and hatchling were photographed in Everglades National Park, the vegetation is typical of the marsh and swamp areas in the southern United States. Large groups of fish, the alligators’ main food, inhabit the warm waters.

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