Evolution of Turtles

Summer 2017
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Turtle Tales

I had the good fortune once again last summer to watch a huge sea turtle lumber back to the water after completion of her nesting duties. She seemed so secure within her protective shell and so stoic in the acceptance of her obligation to continue the traditions of turtle-hood, that I wondered how such a strangely formed creature had ever evolved.

How had they managed to survive down through those vast eons of time while other contenders had faltered and gone extinct? In search of answers, I visited the SCDNR library at Fort Johnson and pulled down a volume by Dr Archie Carr - that grand old man of turtle lore. Who was better qualified to write a book entitled Handbook of Turtles? Here is what Archie Carr had to tell us about the origin and the philosophy of turtles.

(I have taken the liberty of abridging some long passages to conserve space. Also, I have added time-spans in millions of years ago [mya] to aid those, like myself, who do not customarily think in terms of geological epochs.)

“Two hundred million years ago the reptiles, newly arisen from an uncommonly doughty set of amphibians, were on the verge of great adventures. They bore the mark of destiny in the shape of impervious scales and the new cunning to lay shelled eggs and these devices insured them against the age-old disaster of drying out both before birth and after, and let them gratify their growing curiosity about the vast and almost empty land. Today we call these old beasts cotylosaurs,. or stem reptiles. because all the lines of vertebrate life above the amphibian level lead back to them as branches converge in the trunk of a tree.

“The first of the innovations made by the stem reptiles was in a way the most extraordinary and ambitious of all - the most drastic departure from the basic reptile plan ever attempted before or since. By a cryptic series of changes, few of which are illustrated in the fossil record, there evolved a curious and improbable creature, which had a horny, toothless beak and a bent and twisted body encased in a bony box the like of which had never been seen.

“However this skeletal rearrangement may have come about historically, it satisfied the early turtles and allowed full expression of their philosophy of meditation and passive resistance. Down through the faraway Permian [225-280 mya] they sat in their shells and meditated as great events took shape. The coal forests withered, and with the coming of a new climate and flora the archaic animal types began to drop out.

“The Permian ended, and the turtles watched as the main reptile stock found its evolutionary stride and through a hundred million years staged the most dramatic show the world has ever seen - the rise and spread and the incomprehensible decline of the incredible archosaurs. The turtles remained conservative through it all and though some of them took to the sea - sacrificing parts of the beloved shell for greater buoyancy - they always clung to their basic structural plan, as other lines tested and exploited and abandoned a thousand specious schemes.

"They remained unimpressed as Pteranodon cruised the skies and another strain of slim and athletic archosaurs devised Archacopteryx and the birds, and as the Squamata dabbled in mososaurs and snakes. They remained turtles; they even began to prosper as never before, while the dinosaurs bellowed and pounded down through the Jura [136-190 mya] toward their utter and senseless doom in the Cretaceous [65-136 mya], when the last Brachiosaurus laid down his fifty tons to rest and the final tyrannosaur gasped out the anticlimax to nature’s greatest venture in mayhem.

“The Cenozoic [0-65 mya] came, and with it progressive drought, and the turtles joined the great hegira of swamp and forest animals to steppe and prairie, and watched again as the mammals rose to heights of evolutionary frenzy reminiscent of the dinosaurs in their day, and swept across the grasslands in an endless cavalcade of restless, warm-blooded types. Turtles went with them, as tortoises now, with high shells and columnar, elephantine feet, but always making as few compromises as possible with the new environment, for by now their architecture and their philosophy had been proved by the eons; and there is no wonder that they just kept on watching as Eohippus begat Man o’ War and a mob of irresponsible and shifty-eyed little shrews swarmed down out of the trees to chip at stones, and fidget around fires, and build atom bombs.”

Let us hope that we descendants from that “mob of irresponsible and shifty-eyed little shrews” will gain some measure of responsibility and a steady gaze to focus on our own obligations for the long term course of evolution on planet Earth.

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