What is the difference between a turtle and a tortoise? The 23rd May marks "World Turtle Day" - a time to celebrate the amazing diversity of turtles around us - and a good time to consider what makes a turtle, a turtle.
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"Turtle" refers to a group of vertebrates with a bony shell on their back. Unlike Armadillos and other shelled animals, this is not simply a bony growth. Instead it is an evolutionary adaptation of ribs that are fused together to form a hard shell around the internal organs. This body form has been highly successful for turtles. They have inhabited the earth for over 200 million years.
There are 356 turtle species around the world. They include species that live in the sea, rivers, wetlands, estuaries and on land. "Tortoise" is a general term that is restricted to turtles that spend most of their time walking around out of the water. In this way, all tortoises are turtles but not all turtles are tortoises.
Much attention is placed on the seven species of marine turtles that turn up on beaches to lay eggs and spend the rest of their life at sea. But there are many other turtles and some are equally or more threatened with extinction.
Australia is home to 33 species of turtles and they have a range of remarkable adaptations to survive. The northern snake necked turtle lays their eggs under the water.
The pig-nosed turtle in Northern Territory has eggs that explosively hatch when they are exposed to water. The Fitzroy River turtle can breathe from their bums to extract oxygen underwater while diving for long periods. Turtles really are heroes in a half shell.
In total, 61% of turtle species are threatened with extinction or have gone extinct recently. In Australia, the western swamp turtle in WA was thought to be extinct for over 100 years but was rediscovered and is still critically endangered.
Disease has become a major threat for other species, locally, the Bellinger River turtle experienced mass decline from a virus in 2015 and its fate remains uncertain. Invasive species like foxes are a major predator of turtles and their nests and contribute to declines of species in southern Australia.
If we are to keep turtles species around, we have to invest in conservation actions to save them. This World Turtle Day is a day to celebrate these amazing animals and think about how we can each make a difference.