No such thing as a shark? Genomes shake up ocean predator's family tree

"A genomic study of dozens of shark species and their close relatives suggests that the ocean's top predators might also not be a natural biological group, contrary to what studies using more-limited genetic data have suggested. The analysis finds that when researchers look at some 'ultra-conserved' parts of the genome, a peculiar family of sharks called Hexanchiformes might be part of an evolutionary lineage that is distinct from the group that includes all other sharks, as well as skates and rays."

"The results suggest that most animals that people call sharks are more closely related to rays and skates than to hexanchiformshark species - just as Gould pointed was the case for some species called fishes. Biologists call such groups paraphyletic. Whether a grouping of animals is paraphyletic or not doesn't keep most scientists awake at night. But accurate family trees, or phylogenies - including one for sharks - help researchers to chart the evolution of key traits."

"Having an accurate phylogeny is a way forward for understanding the processes that have shaped life. Sharks, along with rays, skates and other sea creatures with a cartilaginous skeleton, are part of a group called chondrichthyes, which shared a common ancestor with bony fish that lived more than 400 million years ago."

A genomic study analyzing dozens of shark species and their relatives suggests that sharks may not constitute a natural biological grouping, similar to how 'fish' is not a true taxonomic category. When examining ultra-conserved genome regions, hexanchiformes appear to belong to a distinct evolutionary lineage separate from other sharks, rays, and skates. This means most animals called sharks are more closely related to rays and skates than to hexanchiformes, making sharks paraphyletic. Accurate phylogenies help researchers understand how key traits evolved. Sharks, rays, skates, and cartilaginous sea creatures belong to chondrichthyes, sharing a common ancestor with bony fish over 400 million years ago.

Read at Nature