Wednesday, 7 August 2019

GIANT TORTOISES & THE ISLAND RULE

Giant tortoises and other organisms that live and evolve on islands undergo a different set of selective pressures than those who live on our continental land masses. We call this the 'island rule'. Species develop unusual traits, becoming larger or smaller than their continental brethren.

Food is often restrictive or unvaried and predators are often reduced or all together absent. We see the evolutionary impact in the Giant tortoises of the Aldabra Atoll and Fregate Island in the Seychelles and Galápagos Islands in Ecuador.

They belong to an ancient group of reptiles, appearing about 250 million years ago and evolving to their large size by the Late Cretaceous, 70 or 80 million years ago. And they are big, weighing as much as 417 kg (919 lb) and can grow to be 1.3 m (4 ft 3 in) long. The Galapagos giant tortoise is a wee bit smaller, weighing 215 kg (475 lb) with the males generally outweighing the females. They snack on plants and some have a slight curve to the shell behind their heads to allow them to reach up a wee bit higher to reach more food. The females lay their eggs in a pit dug specifically for this purpose. Once the hatchlings have incubated, they dig themselves out. I'm sure you've seen the adorable photos or videos of them hatching then making their way to the sea.