http://wego-kids.com/34203-waklert-uk.html Name Meaning:  Border Spine?

view it Location Found:  Oklahoma

Geologic Era:  Late Carboniferous to Early Triassic

Estimated Range:  Modern North America?

Size:  Unknown due to lack of remains, probably under 2 meters long 

Extinction:  Early Triassic (approximately 251 million years ago)

Shown below is the partial remains of a spine attributed to Listracanthus, a relative of sharks.  The specimen is very small, but would have been part of a much larger, more frill like spine set.  Fragmented spines like this are reasonably common finds, though body fossils from this animal are all but unknown.  I am not entirely certain of the full meaning of the “listr” part of the name.  The closest I could find that made sense was the word “leiste” from the Old High German word for “border.”  Given that all of the reconstructions of this creature seem to involve a brush-like border on the animal’s back, I thought this word seemed most fitting. 

The problems with Listracanthus is that, aside from the brush-like spines recovered, its appearance is nearly unknown.  This makes really classifying this animal problematic at best, though most paleontologists are at least comfortable in placing Listracanthus among the chondricthyans, or modern sharks and their relatives.  This does not necessarily mean that Listracanthus looked anything like a modern shark.  Early sharks frequently had a more eel-like appearance (such as Orthacanthus), or had some very unique structures attached to them.  All of the reconstructions I was able to locate show an elongated, eel-like animal with a bushy spine border on its back.  

A past chairman of the geology department at the Field Museum of Natural History, Rainer Zangerl, is supposed to have discovered a full body fossil with brush-like spines.  It is possible that this was a full Listracanthus or Listracanthus-like animal.  Unfortunately, the specimen dried out and crumbled to dust before it could be preserved.  Dr. Zangerl described it as an eel-like animal with a brush border of spines.  I think that all reconstructions must be based off of this description, as they all look very similar.  I have tried to locate photographs or drawings of this specimen, but it would appear that none exist.

Image Credits:

Life Restoration:  By Mutter, R.J. and Neuman, A.G. – Mutter, R.J. and Neuman, A.G. 2006. An enigmatic chondrichthyan with Paleozoic affinities from the Lower Triassic of western Canada. Acta Palaeontologica Polonica 51 (2): 271–282., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=54955298