Cheloniidae Family of Sea Turtles
Phylogeny: Sea Turtles fall into one of two families – Cheloniid Sea Turtles of the Cheloniidae Family and Leatherback Sea Turtles of the Dermchelyidae Family. There are six known species of Cheloniid that belong to the Phylum Chordata. There are seven extinct genera and one extant genus within the Dermchylyidae Family with one living species, the Leatherback Sea Turtle, Dermochelys coriacea. They are in the Class Reptila and the Order Testudines.
Distribution: Cheloniid Sea Turtles are found worldwide in temperate and tropical seas. There are six known species in the Cheloniidae Family of which three species are found along Mexico’s Pacific Coast. Cheloniid Sea Turtles spend the majority of their time in shallow water to obtain access to air for breathing but can dive to depths in excess of 290 m (960 feet).
Morphology: Cheloniid Sea Turtles are air breathing, have hard plates (scutes) covering their shells that are made from a substance similar to the main component of cattle horns, and a three chambered heart. They have a hard, bony, upper (carapace) and lower (plastron) shell covering their bodies. Their ribs and vertebrae are fused to the carapace. Their shells are oval or slightly heart-shaped and are low to reduce drag through the water. Unlike most turtles, Sea Turtles cannot retract their head into their shell. They have beaks instead of teeth, lay eggs, and they have four legs for walking or swimming. Sea Turtles are the only turtles whose front legs are stronger than their rear legs. The legs are modified into paddles to assist with swimming. Their legs cannot support their body weight on land. Sea Turtles lack external ears but have eardrums covered by skin and have good hearing, especially in the lower frequencies. They have a very good sense of smell and good underwater eyesight. They spend the great majority of their life at sea but must come ashore to lay eggs. Cheloniid Sea Turtles are large, with the largest having a carapace length of 2.13 m (7 feet 2 inches).
Ecosystems Roles: Cheloniidae are omnivores that consume algae, cnidarians, crustaceans, fish, mollusks, plants, and sponges. In turn adult Sea Turtles are preyed upon by crocodiles, groupers and sharks. While ashore laying eggs, the females are preyed upon by coyotes, wild dogs, jaguars, and other large predator mammals. Their eggs are also vulnerable to these species, as well as shore birds, insects, and small mammals. Newly hatched juvenile sea turtles are prey for a wide variety of birds, fish, invertebrates and mammals. They lay large numbers of eggs multiple times a year and are long lived which helps to offset the large loss of their eggs and juveniles. In air, they are nearsighted. Sea Turtles have cardiovascular systems that are adapted so that they can spend prolonged periods of time underwater.