Earth’s ultimate survivors: Asteroid that wiped out dinosaurs left sharks virtually unscathed

UPPSALA, Sweden — The city-sized asteroid that smashed into the Gulf of Mexico 66 million years ago wiped out most life on land and water. Gone were the dinosaurs and sea monsters like mosasaurs and plesiosaurs. However, according to recent research, it left sharks virtually unscathed.

An analysis of ancient sharks’ teeth found in Sweden shows diversity remained relatively constant across the catastrophic extinction at the end of the Cretaceous. Scientists at Uppsala University say the mass extinction wasn’t nearly as dramatic for sharks as it was for most other vertebrates, suggesting that sharks are nature’s ultimate survivors.

The finding adds to evidence that the iconic Great White and its cousins are the hardiest creatures on the planet. They have stronger immune systems that enable them to fight off a host of potentially deadly infections.

Shark teeth
Late Cretaceous (Campanian) shark teeth from the Kristianstad Basin, southern Sweden.
(Credit: Benjamin Kear, Bazzi M et. al, PLOS Biology, 2021)

Unstable genes make us vulnerable to age-related diseases. However, sharks have been around for so long their DNA is more tolerant to damage. The ability to repair their own DNA has evolved in ways ours hasn’t – and may hold the secrets to curing cancer and other age-related diseases.

Few shark skeletons have been unearthed mainly because they are made of cartilage which is much softer than bone, and rarely survives fossilization. “Sharks are iconic marine predators that have survived multiple mass extinctions over geologic time. Their prolific fossil record is represented mainly by isolated shed teeth,” the authors write.

The Swedish team scanned 1,239 teeth from 9 species spanning 27 million years. They dated back to between the late Cretaceous 83.6 million years ago and the early Paleogene 56 million years ago. The study is the first global investigation of teeth shapes in multiple shark groups across the end-Cretaceous mass extinction.

Some groups of apex predators, particularly those with triangular blade-like teeth, suffered selective extinctions during the period. This could have been due to the extinction of certain marine animals that they preyed upon. The authors note that this pattern of selective extinctions may reflect an ecological shift from specialist tetrapod predators to more general bony fish diets.

However, this was offset by the rise of other lineages, including mackerel sharks in the Odontaspididae family, such as today’s Great White which evolved much later. They are known for razor-sharp, fang-like teeth adapted for feeding on fish. The expansion coincided with the emergence of finned fish in the early Paleogene.

Mapping of the Great White’s genome has revealed mutations that protect it against cancer and other illnesses. Scientists hope more research could help apply the findings to treating illnesses in humans. Sharks could also help wound-healing and blood-clotting because of their ability to recover quickly from serious injuries.

“Ultimately, our study reveals a complicated morphological response to the end-Cretaceous mass extinction. Shark diversity was unaffected when the dinosaurs were wiped out. It highlights an event that influenced the evolution of modern sharks,” the study explains.

This study is published in PLOS Biology.

South West News Service writer Mark Waghorn contributed to this report.

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