Thanks to a groundbreaking study from Yale University, we may need to rethink the definition of a “shark.”

Evolutionary biologists conducted a DNA comparison among various shark species and their close relatives—including rays, skates, and chimeras—to explore their evolutionary links.

Surprisingly, they found that sharks are not necessarily more closely related to one another than they are to these similar species, challenging the traditional classification of sharks as a single biological group.

According to Chase Brownstein, a doctoral candidate at Yale, “Our study casts doubt on the idea that all sharks, apart from rays and skates, share a common ancestor.” BBC Science Focus.

This research can be interpreted in two ways: either sharks do not form a natural group unless they share an exclusive common ancestor, or rays and skates may simply be categorized as another type of shark.

In total, researchers analyzed the genetic data of 48 different species, studying their complete genomes.

“The genome contains all the genetic information found in our cells,” explained Thomas Near, a professor of ecology and evolutionary biology at Yale. BBC Science Focus.

“By examining entire genomes instead of just a handful of genes, we can gain deeper insights into the relationships between organisms.”

Professor Brownstein elaborated on their approach, stating they explored “how various methods of sampling DNA sequences across the genome impact our understanding of relationships among sharks, rays, and other cartilaginous fishes.”

Evidence from their study was inconclusive. While examining specific DNA segments called exons, they found indications that all sharks might belong to the same family.

Conversely, other analyses suggest that certain shark species, like frilled and horse sharks, could be more closely related to rays than to other sharks.

This implies that these unusual sharks may be distant relatives, separated from the broader shark lineage much earlier in their evolutionary history.

If sharks are indeed a distinct group, biologists can utilize this genetic data to estimate when sharks first emerged in evolutionary history.

“We estimate that this group originated roughly 300 million years ago,” stated Brownstein. “ThisTimestamp corresponds to the last time we shared a common ancestor with modern amphibians, or perhaps slightly later.”

The scientists noted that sharks, skates, and rays represent one of the most ancient lineages of vertebrates—animals characterized by stiff, segmented backbones.

“They are the earliest jawed vertebrates to diverge from their ancestors, providing crucial insights into the first animals to evolve jaws and bony skeletons,” Brownstein continued. “Our aim is to bring attention to this often overlooked segment of the vertebrate tree.”

The Yale study is currently awaiting publication.

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