Sea Turtles

The Life and Evolution of Sea Turtles

Submitted by Merryl Kafka

Ancient, primitive and extinct, Proganochelys, was the forerunner of modern turtles and lived over 220 million years ago. Unlike modern turtles today, it had teeth on the roof of its mouth, strong claws, a terrestrial life-style, and was about 3 feet long. But that’s nothing compared to another ancient, extinct turtlecalled Archelon, that was 15 feet long, weighed up to 6,000 pounds and lived 75million years ago.

Over the millennia, sizes were reduced, claws became flippers (for the marine turtles) and the shells became streamlined. Several lineages disappeared, but today there are seven species: Loggerhead, Kemp’s Ridley, Olive Ridley, Hawksbill, Flatback, Green and Leatherbacks.

Turtles are reptiles, with common traits, such as having backbones, lungs, scales, no teeth, cold blooded, and have internal fertilization, but external development of the eggs. The female releases her eggs via a cloaca, a muscular genital organ under the tail that also receives the sperm, and eliminates waste products. The eggs, averaging in number from 100-125, are deposited in a nest in the sand and the hatchlings will emerge in two to three months. What is most unique is that the temperature of the nest determines the gender of the eggs. Warmer temperatures yield females.

Despite each female laying eggs in several nests throughout the spring nesting season, up to 80% of the nests can be destroyed due to predation from rodents, raccoons, crabs, birds, natural disasters, floods, erosion, loss of habitat, or a fungus. Along Deerfield Beach, where nests are marked and protected, turtle conservators collect tiny Leatherback hatchlings and rear them in safer environments (Gumbo Limbo) and release them when they are larger and have a fighting change to survive.

The diets vary depending on both the species and the age. Green turtles get their name from the green fat and muscle, derived from eating turtle grass (Thalassia) and Sargassum. The young are omnivores, and the adults are herbivores. The Hawksbill, almost hunted to near extinction for the shell, feed on sponges as adults, and the young feed on worms, crabs, small fish, and invertebrates.

The Olympian turtle is the Leatherback. It’s the largest size, 6 ft.; has the largest eggs; is the deepest diver, down to 4,000 ft.; and swims the greatest distance, up to 10,000 miles from the Arctic to the tropics. It is amazing that it gets all of this energy from eating sea jellies!