Hallucigenia

In the last thirty years there has been an explosion of fossil discoveries in China. These have added significantly, perhaps even revolutionized, much of our earlier knowledge of some geological eras. I knew that museums in China have wonderful collections of fossil dinosaurs. I was surprised to find that the new discoveries span a much longer history. The Cambrian, which started about 540 million years ago, and lasted for over 50 million years, is part of this. Our earliest knowledge of the biota of the Cambrian came from the Burgess Shale, found in Canada in 1909. The slow fragmentation of the large super-continent of Pannotia, its warm coastal seas, and the complete lack of land plants still supported an immense variety of aquatic life. One of these animals was the Hallucigenia whose fossil from the Chengjiang shales I saw in the natural history museum in Shanghai.

Model of pre-Cambrian animal Hallucigenia

The fossil looks like a crude sketch. It was first described in 1977, when it was reconstructed upside down and front to back. Walking on seven pairs of spiny legs while waving seven tentacles on its back made it something that could be dreamt up on a trip, hence the name Hallucigenia. It turned out that the blob at one end of its body is not its head, but the contents of its guts squeezed out by the clay which buried it. Finally, with electron microscopy, in 2015, a final picture could be created not only of the way it looked, but also how it walked (what a difference good optics makes!). What the animation above does not show is the circle of teeth around the throat, and that is new information which connects it to the family tree of insects. It was once thought that most of the Cambrian animals left no descendants; this may not be true.