Reconstruction by Marianne Collins
When: Mid Cambrian (~505 million years ago)
Where: British Columbia, Canada.
What:Herpetogaster is yet another one of the odd fossils found at the amazing Burgess Shale fossil locality in British Columbia, Canada. This amazingly weird form is known from several complete specimens, so as strange as its anatomy is, that is what was really there, there is very little speculative interpretation! The body of Herpetogaster is roughly 1-1.5 inches (~3-4cm) long, and is thought to have been tough but flexible in life. The animal had a fairly clearly defined head region, with a centrally located mouth, with a paired set of tentacles on either side. These tentacles are thought to have been softer and more flexible than the relatively firm shaft of the main body. These two main tentacles had many sub-branches and would guide food towards the oral cavity. It is unknown if Herpetogaster was a pure filter feeder or if these tentacles actively ensnared small prey that swam too close in the Cambrian seas. The animal was attached to the substrate by a stolon or hold-fast. A number of Herpetogaster specimens have been found together on a single slab, indicating this animal lived in groups.
Herpetogaster has been placed as a stem Ambulacraria. This is the group that includes echinoderms (starfish, sea urchins, sea cucumbers, etc) and hemichordates (acorn worms). As the living and fossil species in these groups of animals look very different from one another, the identification of a stem member is extremely important for our understanding of the evolution of both groups and helps to answer some questions about the poliarty of character states within each group. For example Herpetogaster is bilaterally symetrical, so therefore it shows that the radial symmetry of the echinoderms is a ‘new thing’ and that the bilaterally symmetry of the acorn worms is the primitive condition, and not a reversal. Additionally, knowing the morphology of a stem taxa on this branch will hopefully lead to the identification of the proper phylogenetic position for other ‘Problematica’ fossils in the Burgess Shale and other Cambrian (and older!) deposits.
I’ve hit several Burgess Shale forms previously, check them out here!
And for more of Herpetogaster specifically, go to the Royal Ontario Museum’s page on the specimen:
They have some great animations!