Western Australian Museum researchers have discovered fossilised teeth from three previously unknown shark species, one of which apparently thrived in WA more than 90 million years ago during an extreme global warming event.

The teeth were found in ancient rocks of marine origin, which today are exposed more than 100 metres above sea level in the lower Murchison River area.

The finds were made by a WA Museum team led by renowned fossil shark expert Dr Mikael Siversson, the Head of the Museum’s Department of Earth and Planetary Sciences.

The teeth are from three species of extinct anacoracid sharks that are new to science: Squalicorax acutus, Squalicorax bazzii and Squalicorax mutabilis.

“These extinct anacoracid sharks belong to the same group (the Lamniformes) as the living white shark, megamouth shark and grey nurse shark to mention a few,” Dr Siversson said.

“Their teeth are similar in shape to those of modern whaler sharks although the two groups are not closely related.

“Based on the size of the teeth, the sharks would have been moderately-sized animals measuring around 1-1.5m in body length.”

The finds date back to the middle part of the Cretaceous period, about 101-93 million years ago.

Anacoracid sharks did not survive the mass extinction that wiped out all dinosaurs, except some birds, at the end of the Cretaceous period about 66 million years ago.

“Two of the new species, Squalicorax acutus and Squalicorax bazzii, occur together in a rock layer about 95 million years old, whereas shed teeth of Squalicorax mutabilis occur in slightly younger layers, about 94-93 million years old,” Dr Siversson said.

The time interval when Squalicorax mutabilis existed is particularly notable, as it was known to mark an episode of extreme global warming, suspected by many scientists to have been caused by enormous outpourings of lava flows on the ocean floor.

The release of vast quantities of CO₂ and micronutrients fertilised the oceans which probably caused algal blooms on a very large scale.

These blooms depleted the ocean’s oxygen reserves and marine rocks of this age are therefore often very dark due to high levels of organic carbon, and layered.

Some organisms benefitted in these circumstances, whereas others—those living and feeding in deeper parts of the ocean—perished.

“The presence of as many as three new species within a single group of sharks demonstrates how little we know about Cretaceous sharks from the Southern Hemisphere,” Dr Siversson said.

“The collected teeth of Squalicorax mutabilis are extremely well preserved, a consequence of the absence of scavengers on an oxygen-depleted sea floor.”

The discoveries were recently published in the Australasian palaeontology journal Alcheringa, which includes innovative 3-D images of the teeth

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Media contact
Tony Malkovic
Acting Communications and Media Manager
Western Australian Museum
tony.malkovic@museum.wa.gov.au