Saturday, 18 February 2012

A New Species Of Armoured Fish

The holotype skull of Dunyu longiforis
Around 500 million years ago, during the late Cambrian, the first ever fish evolved. While they were small, tadpole-like creatures, they had definite scales, complex gills and fins, all the hallmarks of fish, irrespective of how primitive. However they did not become truly diverse until the Ordovician. One of the largest and most important groups were the heterostracans. They were a bizarre group with a scale pattern and structure seen nowhere else in the animal kingdom and a range of body plans, from tadpoles to creatures similar to horseshoes.

In 2011, palaeontologists, led by Dr Zhu Min from the Chinese Academy of Sciences in Beijing, were excavating at the 425 million year old, mid Silurian, Huixingshao, Chongquing Formation, China when they discovered a mysterious skull. At first they thought it belonged to the species Eugaleaspis xiushanensis. Yet analysis of the skull's structure and morphology revealed that it was rather different, so different in fact that it led them to name a new species: Dunyu longiforis.

While the two species are superficially similar, the ratio of lengths in their curved, shield-like skulls are just too different to allow them to be the same species, let alone the same genus. The find gives us a tantalising glimpse into the Silurian oceans; a snapshot in life's evolutionary history.