Famous Hallucinatory Fossil Related to Modern Walking Worm
Hallucigenia, that total oddball fossil from the Burgess Shale may not have been an evolutionary dead-end after all. Evidence shows that it is probably related to an extant species of worms.
This creature was found in the Burgess Shale in Canada over a century ago by paleontologist Charles Walcott. The half-billion year old fossils found there were a Perfecta for science because not only was the soft tissue exquisitely preserved but it showed a tremendous diversity of new body designs at the dawn of multi-cellular life. In fact, all modern phyla existing today (except for one, Bryozoa) can be traced back to this Cambrian-Era Explosion of diversity.
Soft body fossilization is a rare and wonderful thing to paleontologists because generally only hard shells or bones fossilize. It therefore offers a window into ancient extinct creatures that would otherwise be totally lost to us (until we find that cloaked alien science probe recording the entire history of earth for us). Taphonomists study what it takes for biological creatures to become fossilized in stone (from the biosphere to the lithosphere as they say) and they conclude that the chemistry of the clay particles which eventually became the Burgess Shale are largely responsible for the soft-tissue preservation. Many believe that an anoxic or oxygen-deprived environment would be required for this to happen but it seems however that oxygen was indeed present when these fossils formed. It is believed that the reduced permeability of the clay particles themselves prevented oxygen from getting around which would hasten decay and therefore short-circuit any possibility of soft-tissue fossilization.
If you look at some of the early drawings of how this creature looked in life, they famously depict hallucigenia upside down and backwards, with the spines being used as legs and the real legs on its back. Silly scientists, right? Actually no. It is true of course that this was partly due to the sheer bizarreness of this specimen; its name does derive from the word hallucinate after all. The early fossil specimens however only revealed one row of legs. Scientists reasonably concluded that they were likely tentacles, perhaps used to pass food to the head. Once second rows of legs were found (often on a different plane in the rock than the rest of the body) it became obvious what they were.
There has been precious little of this weird ancient animal that linked it to modern organisms which is fine since evolutionary dead-ends are expected and often very fascinating and instructive. There has been for a while though a tentative connection to a legged worm found in tropical forests. They are called velvet worms or more anally, onychophorans. It is this connection between hallucigenia and velvet worms that have recently been greatly strengthened and it all has to do with claws. Both species have a special type of claw that consists of multiple layers. This comes in handy if you occasionally molt. It’s obviously beneficial to have a claw already partially grown and ready for action if you just shed your previous claw. These onion-layered claws then are rare enough (if not outright unique) to clearly link these ancient and modern worms with legs.
- Velvet Worm: melvynyeo
- Claw: Martin Smith
- Upside Down Image: MARIANNE COLLINS