Creature of the Week #8: Hallucigenia

When after almost 100 year science is still not very certain about where to place an animal, you can be certain that is it pretty unusual. No weird creatures list could ever be complete without mentioning Hallucigenia, surely one of the most bizzare animals to ever scamper across the face of the earth. Hallucigenia lived during the Middle to late Cambrian aproximately 500 years ago. Hallucigenia species vary from about a half to three centimeters long and appear to have made a living crawling around on the sea floor scavenging whatever they could find. Upon its initial discovery it was placed in Charles Walcott's worm genus Canadia, which turned out to be a essentially a wastebasket of many completely unrelated animals.

Discovered in the famous Burgess Shales of Canada, Hallucigenia sparsa (so renamed because of its "bizarre and dream-like quality" by Simon Conway Morris in the 1970s.) astonished scientists who knew of no equivalent in the modern animal kingdom. Indeed Morris Conways reinterpretation of Hallucigenia fossils as an example of 'vanished designs', completely unrelated to any modern phylum was used (along with creature #1 Anomalocaris) to support one of the main themes in Steven J. Goulds famous book "Wonderful Life", the notion that the Cambrian was a time of unparrelled experimentation of body designs by nature.



However, in the wake of the discovery of more Hallucigenia specimens in the Maotianshan shale of China as well as other similar similar animals from the same time period, more recent analysis of the fossils have revealed that Hallucigenia is perhaps not quite as alien as was once believed. It turned out that Morris had interpreted Hallucigenia had been upside down! The wiggly tenticles on its back turned out to be legs, and what were thought to have been it legs became spikes on it back. So radical was the reinterpretation that the 'blo'b that was once though of as the head was found to in fact be at the rear end, and in fact a stain on the specimens rather that a preserved portion of the anatomy. As a result of these findings, Hallucigenia is now considered to be related to the curious group of stump legged animal known as Velvet worms (Onychopora) and as a result ancestral to the arthropods.

Some alternative interpretations speculate Hallucigenia to be an appendage of a larger, unknown animal, such a turn of events would this would not be not unprecendented as the example of the conodont shows. http://en.wikipedia.org/wiki/Conodont

Contrast of the old and new intrepretations of Hallucigenia: