The Monthly Marine Fossil Dive: Hallucigenia sparsa

Among all the marine fossils discovered, Hallucigenia sparsa cements itself as one of the most recognizable. Hallucigenia lived 505 million years ago during the Cambrian Period, but remains famous due to its peculiar appearance. Even the University of Cambridge described Hallucigenia as “one of the most bizarre-looking fossils ever found” in an article regarding the fossil. With its worm-like body, spikes, and legs, Hallucigenia has confused the scientific world for years.

Identified by Charles Doolittle Walcott in 1911, Hallucigenia was originally described as “Canadia sparsa” as an annelid – a segmented worm – in Walcott’s “Middle Cambrian Annelids”. It wasn’t until 1977 that Conway Morris found that Hallucigenia was not an annelid at all, but instead an entirely different species. In his reconstruction, Morris displayed Hallucigenia walking on its spines with its tentacles facing upwards. Despite the unusuality of the reconstruction, it would not be adjusted until the early 1990s after paleontologists discovered a Cambrian fossil similar to Hallucigenia. As paleontologists realized that the fossil had spikes on its back and tentacles that acted as legs, Hallucigenia’s fossil was further analyzed, leading Lars Ramsköld and Hou Xianguang to change Hallucigenia’s reconstruction. Hallucigenia was flipped upwards and frontward, correcting its leg and head placement.

However, characteristics of Hallucigenia are still debated. While the creature is identified as a member of the Lopopodia phylum and an ancestor of velvet worms, some scientists debate this placement due to Hallucigenia’s lack of clear characteristics linking them to other animals in evolutionary history. Researchers Dr. Martin Smith and Dr. Javier Ortega-Hernandez from the University of Cambridge argue that Hallucigenia is actually more closely related to tardigrades than velvet worms, which would completely change our modern understanding of arthropods and their relationship to velvet worms. Deciphering Hallucigenia would help scientists decipher how modern animal groups formed and help categorize other Cambrian fossils, placing importance on the odd-looking creature even years after its discovery.

References:

“Hallucigenia sparsa.” The Burgess Shale,

https://burgess-shale.rom.on.ca/fossils/hallucigenia-sparsa/.

“Misunderstood worm-like fossil finds its place in the Tree of Life.” University of Cambridge, 

17 Aug. 2014, https://www.cam.ac.uk/research/news/misunderstood-worm-like-fossil-finds-its-place-in-the-tree-of-life.

“Which Way is Up? Reconstructing Hallucigenia.” UC Museum of Paleontology, 

https://evolution.berkeley.edu/which-way-is-up-reconstructing-hallucigenia/.