What the Turtles Tortoise

When I'm feeling a little older than I'd prefer, I think of turtles. These wonderful animals have a lineage so long that it's hard to even imagine. They apparently separated from other reptiles a staggering 220 million years ago, not long after the earliest dinosaurs first arose; from then on, we would probably have recognised them as turtles. We think, quite rightly, that crocodiles are ancient, but the oldest crocodile-like animal (looking like one, and hunting in water rather than on land, as did their ancestors) is some 120 million years younger than the turtles' grandparent.

Galapagos Giant Tortoise Geochelone elephantopus, Santa Cruz.

Northern Snapping Turtle, Elseya dentata, Howard Springs, Northern Territory.

One of the most obvious aspects of turtledom, and a key part of their fabulous success, is of course the shell. It is in two sections (the plastron beneath, the carapace above) comprised of bony segments, 'borrowed' from the ribs and spine, covered, sealed and strengthened with plated scaley reptile skin. Legs and head are pulled in for protection. Australian turtles pull their necks in sideways (save only the wonderful Pig-nosed Turtle of the Top End, only relatively recently recognised by European Australian scientists, but of course long known to indigenous inhabitants). This is a characteristic of the mostly Gonwanan sub-group, Pleurodira, to which they belong; the Old World turtles and tortoises, Cryptodira, pull theirs directly back in. This isn't just an irrelevant detail, but a deep taxonomic divide. 

a Pleurodire turtle, Yasuni National Park, Ecuador.

Angulate, or Bowsprit, Tortoise Chersina angulata, a Cryptodire, West Cape National Park, South Africa.

The same can't be said of the 'turtle or tortoise?' question. In Australia we tend to use 'turtle' only for the great sea turtles (with flippers), and 'tortoise' for everything else, but elsewhere in the world 'tortoise' refers to the dryland, club-footed members of just one family, Testudinidae. This latter is the generally accepted biological usage too. Maybe it's that we don't actually have any true tortoises down under, but have a need for some!

Many freshwater turtles are fierce hunters; the locally common Eastern Long-necked Turtle is an implacable foe of snails, tadpoles, shrimps and small fish. Most tortoises on the other hand are herbivores (see the Giant Tortoise pic above). 

The ancestors of the Giant Tortoises of the Galapagos archipelago in the Pacific, and of the Seychelles and formerly the Mascarenes in the Indian Ocean, floated there, either 'loose' or on vegetation, some millions of years ago, and increased in size since. They originated from Ecuador and Madagascar respectively.

Galapagos Giant Tortoise, Isabela.

Turtles, Manu River, Peruvian Amazonia.

So, call them what you like - though they tend not to think that tortle and turtoise is funny - but respect these most venerable of vertebrates. They've already lasted at least 50 million years longer than did the mighty dinosaur dynasty, and they're showing no signs of going away any time in the imaginable future.