Sunday, 28 October 2012

The Oldest Turtle On The Planet

Turtles, when it comes down to it, are rather odd creatures. Of course we can easily imagine what your average chelonian looked like, but now consider it in relation to other reptiles. They are flat, wide, with curving fins and a tough carapace covering the top of the body and a second piece of amour, the plastron, on its underside. These are often beautifully patterned, constructed from hexagons and pentagons of bone covered in a layer of keratin, the same substance which makes up fingernails.

They are completely different to the thin, fast, land-dwelling lizards or even other marine reptiles throughout time, such as the plesiosaurs with their slender, dart-shaped bodies and long necks. While today, many species are critically endangered or have a tenuous grip on the wild due to over farming as food and pets, their fossil record shows that they have a diverse and proud evolutionary past.

There was great excitement amongst New Yorkers as a specimen of Archelon ischyros was put on display at the American Natural History Museum for the first time.
The 215 million year old limbs and shell
of the as of yet unnamed species of turtle
People marveled at the site of the extinct turtle with a shell the size of a car.

We know that turtles became giants during the Cretaceous period and were diverse during the Cenozoic era, but their origins are a mystery. A creature called Odontochelys, which lived 220 million years ago, is thought by some to be the first marine chelonian on Earth, but its status was uncertain. Now, fossil evidence has been found which proves beyond doubt that turtles existed at least 215 million years ago.

What is even more interesting is that most early turtle fossils came from the Americas and consisted of fragmentary bones. This new fossil discovery is more complete and comes from Poland. In 2008, Dr Tomasz Sulej was looking for fossils, on the basis of a hunch, in a spoil heap of clay in the town of Poreba, north west of Krakow. In just 15 minutes he found the shell, vertebrae and limb bones of two turtles.

The underside of the shell with its associated vertebrae
One species was similar to another ancient turtle called Proterochersis. The other, smaller specimen was very different to any other species of prehistoric chelonian. Both are still unnamed.They are definitely turtles, however, and the oldest on the planet. 'Each new turtle fossil is invaluable as it could provide clues to their origin,' said Dr Sulej. 'Finding something that has been in the mud for 215 million years, is like bringing it back to life.'

Genetic and molecular studies can predict when animal groups evolved, but in the end, the fossils are needed to confirm the dates and show how they evolved. Some say that the fossil record has been made redundant by these newer dating techniques, but this is not the case. They do not tell us how various evolutionary events happened, only when. Fossils will always be needed, yet in some cases, the evidence will elude us for years.