Modern Shark Family Diversified After Dinosaur-Killing Impact 66 Million-Years Ago

Nearly 66 million years ago, a mass extinction event occurred when a massive asteroid crashed into the face of the Earth and wiped out nearly 75 percent of life on the planet.

The event marked the end of the 80 million-year-long Cretaceous period and resulted in the demise of many animal species, including non-avian dinosaurs. However, if a new study is anything to go by, one animal group benefitted from this incident — ground sharks.

Using fossilized teeth of different shark species, an international team of scientists has come to the conclusion that ever since that mass-extinction event occurred, this particular family of sharks has been proliferating, leading to the expansive biodiversity we see today.

For years, scientists have known sharks survived the mass extinction, but, suffered the loss of some important species. This fact was elaborated when the team of scientists decided to analyze the shape of ancient shark teeth found different parts of the world.

"Unlike other vertebrates, the cartilaginous skeletons of sharks do not easily fossilize and so our knowledge of these fishes is largely limited to the thousands of isolated teeth they shed throughout their lives," Mohamad Bazzi, the leader of the project, said in a statement. "Fortunately, shark teeth can tell us a lot about their biology, including information about diet, which can shed light on the mechanisms behind their extinction and survival."

With this idea, the team conducted the study and explored how different shark species responded to the event. This basically involved noting variations in their teeth and using those traits to define the diversity of different groups.

The analysis revealed ground sharks, aka carcharhiniforms, thrived after the extinction event, but another group, named lamniformes, began to go extinct.

As a result of that change, carcharhiniforms make up the largest group of modern living sharks with more than 200 different species, including Tiger, Hammerhead, and Blacktip Reef sharks. On the contrary, lamniformes, which used to be more dominant during the Cretaceous, are smaller in number.

"Our study found that the shift from lamniform- to carcharhiniform-dominated assemblages may well have been the result of the end-Cretaceous mass extinction," Bazzi added in the statement. "Carcharhiniforms are the most common shark group today and it would seem that the initial steps towards this dominance started approximately 66 million years ago".

Though this work pronounces the effect of the dinosaur-killing mass extinction on a select group of sharks, it does not reveal what processes were responsible for such proliferation and die-off. According to the team, this could be an effect of dietary changes occurring in the aftermath of the extinction such as the loss of marine reptiles and cephalopods like squids and the rise of bony fishes.

The team believes further studies could provide more insight into extinct shark groups, which could ultimately give them ways to prevent further loss of currently endangered shark species.

The study titled, "Static dental disparity and morphological turnover in sharks across the end-Cretaceous mass extinction," was published Aug. 2 in the journal Current Biology.