Are Sharks Even Sharks? New Genetic Study Could Rewrite Shark Evolution.

For centuries, scientists have classified frilled sharks and cow sharks as primitive members of the shark family. A new genetic study now questions whether they are sharks at all.

The study, based on whole-genome sequencing of these ancient species, suggests they may sit outside the family tree that includes all other modern sharks, rays, and skates. If confirmed, the finding could force a fundamental rewrite of shark evolution—and reshape our understanding of how these apex predators evolved over 400 million years.

Sharks have long been grouped together based on shared physical features like cartilaginous skeletons and multiple gill slits. Frilled and cow sharks were considered the most primitive living sharks—living fossils that retained ancient traits. But morphology can be misleading. Genetic tools now allow scientists to peer directly into evolutionary relationships, and the results are challenging decades of textbook wisdom.

The new genomic analysis compared the DNA of frilled sharks (Chlamydoselachus anguineus) and cow sharks (Hexanchiformes) with dozens of other elasmobranch species—the group that includes sharks, rays, and skates. The data revealed that these two lineages diverged from the rest of the elasmobranchs much earlier than previously thought—possibly before the common ancestor of all other sharks. That means frilled and cow sharks might represent a separate branch of the cartilaginous fish tree, not true sharks in the modern sense.

Researchers stress that the work is preliminary and requires replication across more species. But the implications are already stirring debate among evolutionary biologists. If frilled and cow sharks are not classified as true sharks, the entire taxonomy of elasmobranchs may need reorganisation. This could affect everything from conservation priorities to our understanding of how key shark traits—like their immune systems and sensory organs—evolved.

The study has not yet been published in a final peer-reviewed journal, but a preprint has been shared on bioRxiv. The lead author, a marine geneticist at a major research institution (name not disclosed in the initial release), told Forbes that the findings were 'unexpected but robust.' The team used advanced phylogenomic methods to build a high-resolution tree of life for cartilaginous fish.

Critics caution that single-gene or limited-genome studies can sometimes give misleading signals due to incomplete lineage sorting or ancient hybridisation. Nonetheless, the consistency of the signal across multiple genomic regions gives the team confidence. Other ancient shark groups, such as the sawsharks and angel sharks, will now be re-examined to see if they, too, occupy unusual positions.

This new study on shark evolution raises a fundamental question: what, exactly, is a shark? The definition may have to change. Currently, sharks are defined by a set of morphological and genetic criteria. If frilled and cow sharks are excluded, then the term 'shark' might apply only to the more recent, derived group that includes great whites, hammerheads, and reef sharks. That would make the frilled shark a 'shark-like' relative rather than a true shark—a distinction with major implications for how we talk about ocean biodiversity.

The public often imagines sharks as ancient, unchanging predators. This research shows that even our most basic categories are still in flux. Next steps include sequencing more deep-sea shark species and integrating fossil data to calibrate the new tree. Within a year, a revised elasmobranch classification may appear in scientific literature. For now, the message is clear: the shark family tree is getting a long-overdue shake-up.