Turtles evolved in the Triassic Period of the Mesozoic Era, some 200 million years ago, a time when small dinosaurs and the first, shrew-like mammals also appeared. It would not be until the Cretaceous Period (during the reign of T. rex), about 120 million years ago, that sea turtles evolved from their terrestrial ancestors.
Initially represented by four families, seven species of sea turtles survive today; all but one (leatherbacks) are in the same family. Most are omnivorous but the green sea turtle is herbivorous, feeding on sargassum and sea grasses. Among the others, some have unique dietary preferences; leatherbacks feed primarily on jellyfish while hawksbill sea turtles favor sea sponges. All sea turtles, should they survive their gauntlet from the nest to the sea, do not become sexually mature for several decades; from that point on, females breed every 2-4 years, depositing 100 eggs or more in a beach sand nest.
Sea turtles are threatened by a wide range of natural and human-induced factors, including loss of nesting habitat, predation, pollution and collisions with boats. Most hatchlings never reach the sea; eggs are consumed by humans, raccoons and coyotes and the young are picked off by vultures, mammalian predators and a variety of sea birds. Once in the sea, others are consumed by sharks or large fish; while adult sea turtles have long been hunted by humans, that practice has decreased due to modern conservation programs. Yet, the adults remain threatened by chemical pollution of our oceans and by the trash (especially plastic) that is dumped from ships or swept from our coastal towns and cities. On land, adult females may also be killed by humans or other large predators (primarily dogs, coyotes and jaguars).
