Turtles are some of the oldest reptiles, with the earliest ones dating back to about 215 million years. About 300 different turtle species exist, spread all over the world. Research of fossilized remains has revealed that these creatures predate the snakes and lizards. They are one of the most ancient reptiles.
Turtles are reptiles, characterized by their cartilaginous or bony shell which acts as their defense mechanism. The shell develops out of their ribs and grows out to cover their whole bodies, except for the limbs and head.
They are ectotherms or cold-blooded creatures, that control their body temperature through external sources. They can contract their neck, as well as legs, inside their shells, to protect themselves from any kind of danger.
This amazing defense mechanism might be the reason turtles have survived extinction, for millions of years. They have exceptional night vision. An abundance of retinal rod cells enables them to have colored vision and they can see at light wavelengths, ranging from ultraviolet to red end of the spectrum. They have a beak and their jaws are used to chew food. They have no teeth but horny ridges instead, that cover their jaw.
Turtle sizes range from a few inches, to more than six feet. Their lifespan can be very long and the oldest known have lived for more than 100 years. Research has revealed that their vital organs do not show many signs of aging, even when they reach a century, in terms of age. That is why, their genome is being probed currently, for clues about their longevity secrets.
The life cycle of all turtles is similar, although the periods they spend in every developmental stage may vary. Their life is spent on land and in water, as they are adapted for both mediums. Most of them spend a majority of their lifetime in water. Here is a brief outline.
Stage 1: Eggs
Female turtles visit dry sandy beaches to lay their eggs. They dig holes in the sand and lay their eggs in there and cover them in sand. Depending on the species, it may lay one to about two hundred eggs. The eggs are particularly leathery and soft. They could be oblong or spherical, depending on the species.
The gender of the turtle, hatched from the egg, can depend on the incubation temperature. This is known as environment dependent or temperature dependent sex determination. In these species, low temperature incubation environment leads to a male offspring, while high temperatures increases the probability of a female being bred.
The incubation period of different species ranges from two weeks, to as much as two to three months. The mother does not stay to protect or incubate the eggs and they are left to themselves.
Stage 2: Hatchlings
Once the incubation period is over, the baby turtles or hatchlings emerge out of their egg shells by breaking it using their egg tooth (a small bump on their nose). Then they squirm their way out of the sand and start moving towards the sea, as if programmed to do so. This is the most dangerous period in their lives as they are hunted by crabs and birds during their flight to the sea. The ones that survive in this initial stage live out their childhood in the sea, devouring animal and plant matter in the coastal continental shelf areas. These years that they spend in foraging and maturing slowly into adults, are usually known as the lost years
Stage 3: Adults
Depending on the species, it might be about three to five years, after which the hatchlings reach sexual maturity and become adult males and females. Some species do not start reproducing until they are twenty years of age. The adult turtles can be herbivorous or carnivorous, depending on the species. In most species, males are larger than females and may have longer heads. They approach breeding areas at sexual maturity and copulate. After breeding, males return to foraging areas while females lay eggs on beaches and history repeats itself. After laying eggs they return to foraging areas. Females reproduce periodically. Thus, the circle of life for turtles, continues.
Their life cycle is typical and yet different in many of its aspects, from other reptiles. Most of their species populations are dwindling and face the danger of extinction. The primary reasons are human encroachment on nesting areas and being killed for meat and eggs. Efforts need to be undertaken to prevent the extinction of these amazing creatures. It can only happen, when we learn to share this Earth with these creatures and stop disturbing the balance of nature.