todropscience:

FOSSIL BRAINCASE AND THE ORIGIN OF GHOST SHARKS (WHO ARE NOT REALLY SHARKS)

The evolutionary origins of chimaeras -cartilaginous fishes known informally as ghost sharks- are now clearer thanks to the data provided of a computed tomography analysis of Dwykaselachus, an enigmatic chondrichthyan braincase from the ~280 million year old Karoo sediments of South Africa.

Despite their popular name, ghost sharks aren’t sharks in fact are related to sharks and rays, which also have cartilaginous bodies. 

At first place, externally the fossil was supposed to be a symmoriid shark, a group of 300 million-year-old sharks. Internally, the morphology exhibits otherwise characteristically chimaeroid specializations, including the otic labyrinth arrangement and the brain space configuration relative to exceptionally large orbits. Surprisingly the braincase preserves details about the brain shape, the paths of major cranial nerves and the anatomy of the inner ear.

These results have important implications for our view of modern of chimaera origins, add robust proof the phylogeny evolution of this group and shed new lights on the chondrichthyan response to the extinction at the end of the Devonian period.

• lllustration: 

  Reconstruction of Dwykaselachus oosthuizeni by Kristen Tietjen.

• Reference: Coates et al. 2017. 

  A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes. Nature.

• Video: Available in Nature