Wednesday, 24 August 2011

An Exceptional Fossil Which Documents The Food Chain In A Permian Lake

A simple food chain containing  Acanthodes, a temnospondyl amphibian and Triodes
In 2008, a team of palaeontologists led by Jurgen Kriwet discovered a remarkable fossil of an ancient shark called Triodus sessilis preserved belly up on an iron rich bed of siderite. The fossil was well preserved, so well preserved in fact, that the remains of several other creatures were found within its stomach. Two were temnospondyl amphibians called Archegosaurus and Cheliderpeton, the other was the remains of a fish called Acanthodes.

The interesting thing was that the Acanthodes was preserved in the stomach of one of the amphibians. The team were looking at the perfectly preserved remains of a three stage food chain. Such fossils are incredibly useful. They are also very rare as the consumed organisms are usually digested completely before fossilisation can occur. For such a fossil to occur would require the meals to have been captured and then the entire group to die and be buried out of the reach of decomposers and scavengers within a few minutes.

However what does this tell us about the ecosystems in Permian Lakes. For an accurate picture, additional specimens would be needed. However if we assume that such a fossil gives us a clear representation of a part of the food web in the lake, it shows us that fish were probably very low down on the food chain, perhaps plankton and algae feeders. Amphibians would have been common predators. However not even they would have been safe from the sharks.