The Digester

A genomic analysis of 48 cartilaginous fishes finds conflicting trees depending on which genomic regions are used, and ultra-conserved DNA regions suggest hexanchiform sharks may sit outside the main shark lineage, which would make most sharks more closely related to rays and skates.

Yale researchers Thomas Near and Chase Brownstein compared genomes from 48 sharks, rays and relatives using 840 protein-coding genes and about 350 ultra-conserved regions.
Protein-coding genes recover the traditional tree with sharks as a single group separate from rays and skates.
Ultra-conserved regions instead place hexanchiforms outside the main shark lineage, implying rays and skates may be nested within sharks and that flat-bodied rays could have evolved from shark-like ancestors.
Hexanchiformes include cow sharks and frilled sharks that have six or seven gill slits and primitive jaws, and they form the divergent lineage in the ultra-conserved analysis.
The work is a bioRxiv preprint that has not been peer reviewed and the authors say more species sampling and genetic markers are needed to confirm the relationships.

Genomes suggest sharks might not form a single evolutionary group

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