Loftwings and Demons

Hallucigenia is the adorable new face of your nightmares

One thing I find fascinating is following the history of a scientific discovery.  I think it's worthwhile to know who was involved in the research, what conclusions they drew, and importantly, why they came to the conclusions they did.

I've linked an article that shows the current reconstruction of the Cambrian animal Hallucigenia.  When this creature was originally identified as distinct from other known animals in 1977 by Simon Conway Morris, little was known about it [1].  Morris recognized that the fossil wasn't part of the Canadia genus, as was originally believed when it was first catalogued by Charles Doolittle Walcott in 1911.  He also attempted a reconstruction of the creature based on the limited fossil evidence available at the time, showing it with a bulbous head, a tail, walking using its large 'spikes' as legs, and using a series of tentacles on its back to pass food to its mouth.  With such an apparently puzzling body plan, it was proposed that Hallucigenia was an evolutionary dead end that had left no descendants.

In 1991, a paper by L. Ramskold and Hou Xianguang would be published that would literally turn Hallucigenia upside down [2]. Using additional fossils of the creature from Chengjiang, China, Ramskold and Xianguang gave compelling evidence that a number of the tentacles were actually clawed feet and the spikes armor along the back of the creature. 

Then, in June 2015, a discovery described in a paper by Martin R. Smith and Jean-Bernard Caron, would again flip the perception of Hallucigenia, this time from head to tail [3].  Examining fossils with new electron microscope technology, it was possible to identify the eyes of the fossil for the first time--on the end Conway had identified as the tail.  The bulbous stain believed by Conway to have been the head turned out to actually be waste materials excreted by the creature after death.  In addition, the researchers were able to make out a row of teeth, causing them to reclassify Hallucigenia as an ancestor of a wide range of modern animals, from roundworms to lobsters to tardigrades.  

The linked Wired article [4] includes a video that shows a Hallucigenia fossil to scale and also gives a nice cgi reconstruction of the creature based on our understanding of it today.  But I thought it would be fun to track down some more of the specifics of the science as well, hence the inclusion of the actual scientific papers.

References:

1. Hallucigenia. http://www.prehistoric-wildlife.com/species/h/hallucigenia.html.

2.  New early Cambrian animal and onychophoran affinities of enigmatic metazoans (1991: Lars Ramskold, Hou Xian-Guang. Nature, Vol. 351, pp. 225-228)
https://www.academia.edu/1781225/New_early_Cambrian_animal_and_onychophoran_affinities_of_enigmatic_metazoans_1991_Lars_Ramskold_Hou_Xian_Guang_Nature_Vol_351_pp_225_228_

3. Hallucigenia’s head and the pharyngeal armature of early ecdysozoans
Martin R. Smith & Jean-Bernard Caron
https://www.nature.com/articles/nature14573

4. Hallucigenia is the adorable new face of your nightmares.
https://www.wired.co.uk/article/hallucigenia-worm-head-discovery