新课标高二选修7 Unit3 Under the sea全套教案 - 图文

by the number and pattern of scutes on the carapace. The shell is considered the most highly developed protective armor of any vertebrate species. While most land turtles can retract their heads into their shells for added protection, sea turtles cannot and their heads remain out at all times. Color

Green Sea Turtles have green flesh. The carapace is olive brown to black, while the plastron is pale yellow to creamy white. The carapace is molted, variegated in color. Rarely will you find a Green Sea Turtle with a solid colored shell. Counter-shading of the shell conceals the turtle from predators, making it difficult to distinguish the dark carapace from the sea floor and the light plastron from the lighter sky. Size

Green Sea Turtles as hatchlings weigh about an ounce and have a carapace length of 2 inches. A sexually mature green sea turtle weighs 200-350 pounds with a carapace length of 2.5 feet. Adults grow to a carapace length of 3.5 feet and weigh an average of 400 pounds. One of the largest turtles that ever lived from the Late Cretaceaus period, 144 to 65 million years ago, reached a length of 9.8 -13 feet. Lifespan

The lifespan of sea turtles is not known. It is believed that Green Sea Turtles reach sexual maturity around the age of 25 years and can live up to 80 years of age. The long period of maturation helps to explain why it takes turtles so many years to recover from a population decline. Shape

Sea turtles are wonderfully adapted to life in the ocean. Their shells are lighter and more streamlined than land turtles. Front and rear limbs have evolved into flippers. These flippers make sea turtles efficient and graceful swimmers, capable of swimming long distances in a short time.