Saturday, 16 October 2010

Archelon ischyros: who was he?

The world was looking slightly different 75 million years ago: the climate was a tad warmer, dinosaurs were still roaming the earth (not for much longer though) and the different tectonic plates were much nearer to eachother. North America was separated by the Western Interior Seaway (W.I.S.) in two different regions: Laramidia and Appalachia, and the “modern” species of fish were just starting to form. The name of this epoch was Late Cretaceous (last period of the Mesozoic era.)
If we could have dived in the W.I.S. we would have had a good chance of bumping into a very special type of sea turtle, more or less the equivalent of our Leatherback. The likeness, though, would have stopped there because instead of saying something like “WOW! Look at that wonderful Leatherback.” we would have just said “Ah....” and then collapsed with a heart attack: it was 4.5m long, 5m and weighed around 2,000kg! Ladies and gentlemen, I give you the Archelon ischyros, the biggest turtle in the world. Even the physical appearance would have not been too close to the Leatherback: the carapace wasn't hard but a soft leathery layer on a boney structure, it had a pointy tale and a small skull. Actually, the graphic reconstruction of it portrays it as a very ugly creature, with huge flippers, a scute-less carapace and a huge jaw. If you want to take a peek you can find it here.

As in every ecosystem, in the Late Cretaceous there was a food chain and the Archelon fed mainly on cephalopods (squid) while it was hunted by the Tylosaurus. This was a type of sea serpent, 15m long, with a long line of very sharp teeth and an appetite like a wolf. Can you imagine eating a creature as big as 20m2 ? At the end of the Cretaceous period, about 65 million years ago, the Archelon became extinct and along with it the majority of the dinosaurs and other species of animals and plants. At that point the Cenozoic era began which brought the advent of mankind.

How did the Archelon become extinct? If I knew, I would be the most famous Palaeontologist in the world. Surely, given the absence of the humans, the causes would have been natural: feeding specialisation, changes in temperature, brumation... The fact is that, at the beginning of the Cenozoic, the Archelon is no more. So, how do we know it existed? One fine day in 1895, Dr. G.R. Wieland was pegging along on a rock formation in South Dakota when his hammer met a strange shape. Few days later Dr. Wieland brought home an almost entire skeleton of the Archelon, as the picture shows. I am sure you can appreciate the dimension of it. Almost a century later, in the 70s, a bigger skeleton was found almost in the same spot. So, when you see a Loggerhead or a Hawksbill or even a Leatherback just think at how long it took to evolve to this stage…

1 comment:

  1. Anonymous 5 May 2012 17:49

    Thanks this really helped me with my science project!