Sunday, 5 July 2015

Hallucigenia Gets A Close Relative

The Cambrian Explosion produced a multitude of oddities. One of the strangest was Hallucigenia. Its characteristics baffled palaeontologists, but in recent years we have confidently reconstructed its anatomy and established its evolutionary relationships. It is an ancestor to the velvet worms or onychophorans to give them their proper name. Among Cambrian organisms its morphology is fairly unique. A new fossil discovery, however, gives Hallucigenia a close relative. The fossil was not discovered at the classic Cambrian site, the Burgess Shale, nor at its sister locality the Chengjiang shales. It comes from a relatively unexplored new site, the Xiaoshiba deposits, which has a stratigraphy comparable to that of Chengjiang.
The fossil of Collinsium from the Xiaoshiba deposits in China

Given the name of Collinsium, its similarities to Hallucigenia are apparent. 'Both creatures are lobopodians, or legged worms, but the Collins' Monster sort of looks like Hallucigenia on steroids,' said Dr Javier Ortega-Hernández from the Department of Earth Sciences at the University of Cambridge. 'It had much heavier armour protecting its body, with up to five pointy spines per pair of legs, as opposed to Hallucigenia's two. Unlike Hallucigenia, the limbs at the front of Collins' Monster's body were also covered with fine brushes or bristles that were used for a specialised type of feeding from the water column.'

Additionally the structure of the spines - a cone in cone construction - was identical to that found in the spines of Hallucigenia and the claws of modern day velvet worms, further underpinning their close relationship. 'There are at least four more species with close family ties to the Collins' Monster, which collectively form a group known as Luolishaniidae. Fossils of these creatures are hard to come by and mostly fragmentary, so the discovery of Collinsium greatly improves our understanding of these bizarre organisms.'

Its legs and claws were not suited to navigating a muddy sea floor. It is likely that Collinsium clung to the sides of sponges. Such a position would also place it in a prime position in the water column for filtering out nutritious particles. 'Modern velvet worms are all pretty similar in terms of their general body organisation and not that exciting in terms of their lifestyle,' said Ortega-Hernández. 'But during the Cambrian, the distant relatives of velvet worms were stunningly diverse and came in a surprising variety of bizarre shapes and sizes.' Collinsium adds to a crowded sea floor of Cambrian oddities.