Well here it is! Friday’s mystery fossil is an acanthodian, an ancient group of fish which include the earliest known jawed vertebrates. The mysterious bivalve-like structure is actually the pectoral fin of Brochoadmones milesi from the Devonian of Canada’s Northwest Territories.
Congrats to The Brummell who came closest with the suggestion that the spines were of an ancient shark, similar to the modern spiny dogfish (Squalus acanthius). Indeed, acanthodians share many characteristics with sharks.
That was extra tough, don’t worry the next one will be easier!
Hanke, G.F. and Wilson, M.V.H. 2006. Anatomy of the Early Devonian acanthodian Brochoadmones milesi based on nearly complete body fossils, with comments on the evolution and development of paired fins. Journal of Vertebrate Paleontology 26:526-537.