What Is a Shark? A New Genetic Analysis Throws an ‘Unexpected Wrench’ Into Our Understanding of the Ocean Predators

Some shark species might belong to their own distinct lineage, which is separate from all other sharks, rays and skates, according to a new study

Sarah Kuta | Daily Correspondent

April 8, 2026

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The shark family tree might be more complicated than previously thought.

Scientists have long assumed that sharks are a natural group, meaning that all shark species are more closely related to one another than they are to relatives like rays and skates. But a new genetic analysis, posted February 15 on the preprint server bioRxiv, challenges this assumption. The results, which have not been peer-reviewed, suggest some shark species belong to a distinct lineage separate from all other sharks, rays and skates, indicating that scientists may need to rethink how to define the ocean predators.

The findings throw “an unexpected wrench into our understanding of the relationships of some of the oldest living vertebrate clades,” the researchers write in the paper.

Sharks, skates, rays, chimaeras and other fish with flexible, cartilaginous skeletons are members of a group called Chondrichthyes. They’re separate from Osteichthyes, or fish with skeletons of hard, rigid bone.

Chondrichthyes includes more than 1,200 living species, and the group dates to at least 439 million years ago. Though these creatures have been around for a long time, scientists still aren’t sure how they’re related to one another.

Evolutionary biologists Thomas Near and Chase Brownstein, both at Yale University, wanted to get to the bottom of this mystery. So, they examined the complete genetic instructions, or genomes, of 48 species representing all major living lineages of chondrichthyans.

The duo investigated two types of genomic data: protein-coding sequences that tend to be shared across all species within a group, and ultraconserved elements, or regions that evolve slowly and change very little over time.

Each type produced a different version of the shark family tree. The protein-coding sequences confirmed the longstanding idea that all sharks all share a common ancestor, exclusive of rays and skates. But the ultraconserved elements suggested that some shark species, a group known as Hexanchiformes, branched off early and formed a sister lineage to all other sharks, rays and skates.

Hexanchiformes include cow sharks and frilled sharks, which have six or seven pairs of gill slits, instead of the usual five found on other shark species. These creatures have also retained the ancestral jaw structure of cartilaginous fishes.

“This can be read two ways: Either sharks are not a natural group, insofar as they don’t share exclusive common ancestry, or rays and skates are simply another type of shark, ” Brownstein tells BBC Science Focus’ Hatty Willmoth.

Based on their investigation, Near and Brownstein believe the family tree that has Hexanchiformes as a separate, sister lineage is correct. But to prove it, they’ll likely need to sequence the genomes of additional shark species and investigate other genomic data.

However, some scientists wonder whether this type of data alone can tell the whole story. Bits of genetic evidence have likely disappeared over the last 439 million years, making it difficult to piece together the creatures’ relationships.

“People revere sequence information more than they should,” Gavin Naylor, an evolutionary biologist at the Florida Museum of Natural History who was not involved with the research, tells Nature’s Ewen Callaway. He says anatomical comparisons can help fill possible genetic gaps.  

Still, establishing an accurate family tree could have important implications for evolutionary biology, biomedical research on jaw development and more, the study co-authors say. The findings may also support efforts to protect the ocean predators, which face numerous threats in the modern world.

“Sharks hold more evolutionary history than any other vertebrate lineage,” Brownstein tells Nature. “We need a good tree to understand what we stand to lose.”

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.