Oft-times people ask me about 'turtles', I've used inverted commas here, you'll soon understand why. It seems to me there is much confusion surrounding the terms; turtle, tortoise and terrapin. And while I agree the definitions are not clear, understanding these animal's lifestyles however, is actually fairly easy when you look at their bodies. Very few things in nature are a result of happenstance; an animal's physiology is a reflection of where it lives, and this article we highlight the different survival strategies of the turtle.
Irrespective of what you call them, these animals I'm discussing today are easily recognisable by the shells they wear on their backs. Shells are not going out of fashion anytime soon; in fact these animals have been lugging them around for millions of years. They are very successful (shells are) and have been modified in many ways, but I'm not going to spend much time talking about shells because in this article it's much ado about feet and flippers!
Green Sea Turtle at Lady Musgrave Island, QLD
We'll start with this guy (above), or rather girl. How do I know it's a girl...bear with me it should become clear in just a bit. She is a kind of marine or sea turtle, I've even heard of these animals being described as 'true turtles'. She is completely aquatic, and thus has flippers rather than feet, all the better to swim with my dear! One of the facts I find particularly charming about these creatures is that despite their sea-faring bodies, they are obligated to land because the female lays her eggs ashore. The males however, spend only a few minutes in their entire lives (which may be 100 years or more) ashore. Those few minutes are spent desperately scurrying as newly hatched babies towards the sea, and they never come back to land ever again, they even mate in the ocean. The ocean has molded their bodies so dramatically that the business of laying eggs is extremely difficult (bordering on treacherous) for the female.
Galapagos Tortoise at Australia Zoo, QLD
Next up, is the handsome fella above. I'm referring to the tortoise, not the Joel. This is a giant Galapagos tortoise, and it is just that-a giant! It's the largest living tortoise; the very biggest individuals can weigh over 400 kg [1]. Similarly the Galapagos tortoise and it's smaller cousins are all land dwellers, and so it only makes perfect sense that they should have feet rather than flippers, and certainly they do. The Galapagos tortoise not unlike Darwin's finches show amazing divergences in form across different islands. The shape of one's shell is a reflection of the kind of diet a tortoise will have. Simply put, those with 'saddleback' shells can eat a variety of plant material including the foliage from low growing trees, whilst dome-shaped shells restrict a tortoise to eating only grass. The term 'tortoise' is perhaps the most well-accepted name given to these club-footed turtles that don't swim. However, because tortoises do not occur in Australia, some Aussie's have taken to calling some kinds of native turtles 'tortoises' as a way of distinguishing those that swim in the ocean from those that swim in freshwater.
'Stanley' the Long-necked turtle on show, Gold Coast, QLD
The last kind of turtle, the freshwater turtle has clawed, webbed feet (with one exception), the best arrangement I'm sure you'd agree for an animal that needs to swim mostly and walk occasionally. The freshwater turtle perhaps causes the most confusion when it comes to terminology. Turtle, tortoise and terrapin have all been used at some point to refer to this creature. But whatever you choose to call it, the only important thing to remember is it's lifestyle has shaped it's body. We know the freshwater turtle is more closely related to a tortoise than to a marine turtle. Science explains from an evolutionary point of view that the freshwater turtle is in fact a tortoise that went back to living in the water.
Ultimately, the term 'turtle' describes all of these shelled reptiles discussed above, but sea turtles, tortoises and freshwater turtles live very different lives and now you know what's who, and who's what, I hope...?
1. Ebersbach, V.K. (2001) The biology and husbandry of the Aldabra Giant Tortoise (Geochelone gigantea) and the Galapagos Giant Tortoise (Geochelone elephantopus) in captivity with special reference to reproduction. Tierärztliche Hochschule, Hannover