Shark Week: Spiny Sharks!

Several acanthodians by Nobu Tamura.

So yeah, shark week! How about we go all the way back into the ancestors of sharks, the Acanthodii, also cleverly known as “spiny sharks”?

Originally thought to be early teleosts, several phylogenetic studies in recent years have firmly placed acanthodians as stem-chondrichthyes*! Some forms like Doliodus are even “missing links”, sharing some traits with bony fish latter lost in sharks and rays.

*The ancestors of bony fish, meanwhile, are nested among placoderms or similar forms. Also cool.

Acanthodians were a successful group, having diversified ina menagerie of forms both in salt and fresh water, often resembling modern bony fish in shape. They survived the Devonian extinction, albeit with heavy casualties, and by the mid-Permian they went extinct. Such a bummer!

They are easily my favourite ancient aquatic vertebrates, and though they still live on through their modern cartilaginous descendents, it’s neat to imagine a world where their grade survived….