Thursday, 19 January 2012

A New Species Of Enigmatic Stalked Animal From The Burgess Shale

A fossil of Siphusauctum gregarium
The Burgess Shale is perhaps the most celebrated locality in all of palaeontology. Since its discovery in 1909, over 65,000 specimens have been extracted, composed of around 150 different species, which include Earth's first super-predators and the earliest forms of many of the animal groups alive today. Over the years, different species have been identified from the specimens collected by Charles Doolittle Walcott, such as Tegopelte, a centipede-like creature which scuttled with great speed across the Cambrian sea bed.

Now Dr Jean Bernard Caron, curator of the Royal Ontario Museum's collection of invertebrate fossils, amongst which is the largest collection of Burgess Shale specimens anywhere in the world, believes that he has identified yet another new species. The importance of the fossil beds were brought to light by the eminent Stephen Jay Gould. In his book, Wonderful Life, he describes Doolittle Walcott as having 'shoehorned' all the fossils into existing phyla, failing to recognise differences between the species.

While this has been described as a harsh view of his work, it does hold some truth. It is for this reason that new species have been described from the old fossils. Dr Caron was looking at fossils of a strange, crinoid-like animal called Siphusauctum gregarium, when he realised that they were unlike any other members of the class they had been grouped into. Surprising, considering that it was one of the most common organisms at the Burgess Shale.

A reconstruction of Siphusauctum gregarium 
The creature was 20 centimetres in length and composed of a single stem topped with a large, ovoid feeding structure. The structure, properly known as a calyx, was composed of six segments, each with a small opening at the base and a single anus at the top, which was enclosed in a flexible sheath. The middle of the structure housed a stomach linked to each opening by a tube. A single gut connected the stomach with the anus. Each creature existed as part of a colony.

It is likely that they were filter feeders, passing water through the openings, through the stomach, ejecting the waste water, whilst absorbing the nutrients via the gut. Even though its morphology has been reconstructed, its relationship with other organisms is unclear. While other stalk-based filter feeders have been discovered, a lack of small tentacles common to these means that it is not especially closely related to them. Its unique feeding system means that it is unlikely to be ancestral to organisms that either appear later in the fossil record or that are alive today. Dr Caron places it, therefore, in a completely new class of invertebrates.