Thursday, 8 December 2011

The Ancient Eyes Of Anomalocaris

The exquisitely well preserved eyes of Anomalocaris canadensis
Anomalocaris canadensis was the first large super-predator on Earth. At a metre in length, covered in plate armour with two spiked claws and a mouth filled with sharp teeth, this beast dominated the oceans for many millions of years. When the first partial fossils of Anomalocaris were discovered in the 1920s by Charles Doolittle Walcott, they were incorrectly identified as belonging to two different species (the circular mouth, some strange type of jellyfish, and the grasping claws as a species of shrimp or worm).

Since these early discoveries, we have built up a far more accurate picture of this early predator. We know what it looked like, what it ate and how it lived. Now remarkable new fossil evidence reveals the complexity of its eyes.

All top predators possess remarkable eyesight. Trilobites showed that large complex eyes had evolved by the time Anomalocaris was dominant in the oceans. Palaeontologists assumed that it also had eyes of, at the very least, a similar quality and level of sophistication.

Numerous anomalocarid fossils have been discovered which show where the eyes were placed on the head and roughly what shape they were, yet there was no evidence to indicate how powerful they were. In June 2011, a team of scientists collecting fossils from a 515 million year old formation on Kangaroo Island just off the coast of Adelaide, South Australia, found a series of fantastically preserved specimens.

It was immediately apparent that these eyes were sophisticated and very powerful but the scientists had yet to identify which creature they belonged to. A comparison to various fossils of the Cambrian biota quickly allowed them to match the marvellous lenses to Anomalocaris. The stalked-eyes were over three centimetres long, making them the largest arthropod examples ever. They were composed of more than 16,000 lenses giving it an exceptionally sharp image with very little lensing at the edges.

The discovery is ground-breaking as it shows that Anomalocaris was a very formidable predator. Its size and morphology, combined with a global distribution in China, Australia to Canada, and eyesight that was superior to all known species of living insects or crustaceans, made it one of the most succesful Cambrian organisms. It secured its dominant position for more than 10 million years, making it one of the most important carnivores ever to have stalked the Earth.