One of the earth’s most ancient animals, the turtle has been around for more than 200 million years, emerging sometime in the late Triassic period.
Sea turtles however emerged a little bit later, coming around some 110 million years ago. Of the first species that were introduced, only seven now remain the world today, those being (picture is on the top, name is on the bottom):
Green turtle (Chelonia mydas)
Loggerhead (Caretta caretta)
Leatherback (Dermochelys coriacia)
Hawksbill (Eretmochelys imbricata)
Olive Ridley (Lepidochelys kempii)
Kemp's Ridley (Lepidochelys kempii)
Flatback (Natator depressa)
The Evolution of Sea Turtles
Although not yet verified, many paleontologists believe that modern day turtles and tortoises derive from a creature called eunotosaurus (you-NO-toe-SORE-us), which is Greek for ‘original noded lizard’.
Eunotosaurus lived during the Permian period, some 250-300 million years ago, and had a pronounced, sort of ‘proto-shell’ that contained its elongated ribs.
It is because of this proto-shell that scientists believe would eventually evolve into the carapaces (turtle shells) of modern day chelonians.
Some 60 million years ago, what first most likely started as the wide-ribbed eunotosaurus would give rise to creatures such as the two-ton protostegas, which from the outside looked very similar to the modern leatherback.
Common Features of Sea Turtles
Unlike their land-dwelling cousins, sea turtles are unable to retract their necks, heads and legs into their shells.
Their shells are what we would consider to be ‘streamlined’, which means that they are hydrodynamic so that water can glide over and around their bodies very easily.
All sea turtles also possess flippers, instead of legs with claws (freshwater turtles) or stumps (tortoises), which can propel them through the water at fast speeds.
Of all seven of the sea turtle species, only one of them, the leatherback, is soft-shelled. The other six are all hard-shelled.
Because of this, sea-turtles can be put into two categories; Dermochelyidae (soft-shelled) and Cheloniidae (hard-shelled).
Sea turtles can easily swim under the water for at least 45 minutes, and when resting, are able to stay underneath the water for several hours.
Because sea turtles do not possess glands and consume large amounts of water every day, they pump out excess amounts of seawater through their tear ducts.
Size of Sea Turtles
The largest of all sea turtles, the leatherback, can reach sizes of 2,000 lbs and seven feet in length.
The smallest, the Kemp’s ridley sea turtle, clocks in at around 100 lbs and from 2.5 to 3 feet in length.
Green sea turtles, the largest of the hard-shelled sea turtles, can reach sizes of 700 lbs and up to 5 feet in length.
The Diet of Sea Turtles
Although all sea turtles live in the water, their diets can be quite diverse. Unlike the other sea turtles, green sea turtles for instance are herbivores (plant eaters), preferring to munch on things like huge amounts of seaweed and algae.
When they are young, they are omnivores, but with a strong preference for food such as crabs and jellyfish.
The Kemp’s ridley sea turtle, the smallest of the bunch, enjoys eating animals such as jellyfish, mollusk and smaller fish found in muddy and sandy waters.
The largest of all the sea turtles, the leatherback, especially enjoys dining on jellyfish.
Unfortunately, because bits and pieces of plastic in the ocean often times resemble jellyfish, leatherbacks will sometimes consume and swallow plastic and die as a result.
The loggerhead, which possesses exceedingly powerful jaws, likes to feed on shelled animals such as crabs, mollusks, shrimp, lobster and other crustaceans along shallow shorelines. If you love loggerheads, you should check out my list of the best books about sea turtles.
The hawksbill’s main source of food is sponges, whereas the flatback and olive ridley will both consume crabs, mollusks, algae and jellyfish.
Conservation and Sea Turtle Distribution
All seven species of sea turtles have the same general living environment, that being the mostly warm and temperate waters around the equator and both tropics.
The leatherback, as mentioned elsewhere, can migrate and travel a bit further north and south into colder waters.
Unfortunately for all seven species of sea turtle, human activity has significantly dwindled their numbers.
These are the following estimates for their numbers in the world today.
Olive Ridley Turtle
Kemp's Ridley Turtle
Green Sea Turtle
~85,000 to 90,000 females
~20,000 to 23,000
Because most of their lives are spent in water, scientists and conservations do not have a lot of experience and information on their behavior.
Nearly all of that comes when they are able to observe them, when female sea turtles come ashore to nest and lay their eggs.
With the exception of the warmer-blooded leatherback, sea turtles internal body temperature is largely determined by their outside environment.
The colder the environment, the less active they become.
When it comes time for them to rest underneath the waves, their heartbeat will drastically reduce in order to save more oxygen. In fact, as much as nine minutes may elapse between heartbeats!
Sea turtles do not rear their young.
Instead, they will come ashore, bury a hole in a suitable place, lay their eggs and then return to the ocean. It is estimated that because of poachers and various predators, only one out 1,000 turtle hatchlings even makes it into the water.
Although the box jellyfish is arguably the deadliest animal with respect to humans, its powerful toxin has no effect on leatherbacks, who greatly enjoy feasting on them.
According to ancient Hindu mythology, the world is held up by four elephants, all of whom stand upon an enormous turtle which then gives them support.
The indigenous native Americans had a similar belief regarding a ‘World Turtle’, in which stacks of turtles hold up the earth.
According to old Chinese mytholody, the turtle represents wisdom and longevity.