Before Megalodon, researchers say a monstrous shark ruled the ancient Australian seas

WELLINGTON, New Zealand (AP) — In the age of dinosaurs — before whales, the great white or the bus-sized Megalodon — a monstrous shark roamed the waters of what is now northern Australia, among the sea monsters of the Cretaceous period.

Researchers studying a giant vertebrate found on a beach near the city of Darwin say the creature is the earliest known mega-predator of the now modern shark lineage, which lived 1.5 million years before the first giant sharks.

And it was big. The ancestor of today’s 6-meter (20-foot) great white shark was thought to have been about 8 meters (26 feet) long, said the authors of a paper published in the journal Communication Biology.

“Cardabiodontids were ancient, mega-predatory sharks that have been very common since the late Cretaceous, about 100 million years ago,” said Benjamin Kerr, senior curator of paleobiology at the Swedish Museum of Natural History and one of the study’s authors. “But it pushes back the envelope of time when we’re going to find really giant cardabiodontids.”

Rediscovered fossils point to a large shark

Sharks have a 400-million-year history but the ancestors of today’s great white sharks, appear in the fossil record 135 million years ago. At the time they were small – perhaps only a meter in length – which made the discovery that 115 million years ago lamniforms were already gigantic a surprise to researchers.

The vertebrates were found on the coast near Darwin in the far north of Australia, from what was once an ancient ocean floor that formed Gondwana – now Australia – Laurasia, which is now Europe. It is an area rich in fossil evidence of prehistoric marine life, with long-necked plesiosaurs and ichthyosaurs among the creatures so far discovered.

The five vertebrates that started the search to estimate the size of their mega-shark masters are not a recent discovery, but an old one that had been somewhat overlooked, Care said. Discovered in the late 1980s and 1990s, the fossils measured 12 centimeters (4.7 inches) and were stored in a museum for years.

When studying ancient sharks, vertebrates are a prize for paleontologists. Shark skeletons are made of cartilage, not bone, and their fossil record consists mostly of teeth, which sharks shed throughout their lives.

“The importance of vertebrae is that they give us clues about shape,” Carey said. “If you’re trying to measure it by the teeth, it’s hard. Are the teeth big and the bodies small? Are they big teeth with big bodies?”

Ancient shark shape still holds mystery

Scientists have used mathematical formulas to estimate the size of extinct sharks such as Megalodon, a giant predator that came later and may have reached 17 meters (56 feet) in length, Care said. But the rarity of the vertebrae means it’s difficult to answer questions about ancient shark sizes, he added.

An international research team spent years testing different methods to estimate the size of Darwin’s cardabiodontids, using fishery data, CT scans and mathematical models, Care said. Eventually, they arrived at a possible picture of the size and shape of the predator.

“It looked for all the world like a modern, giant shark, because that’s the beauty of it,” Kear said. “It’s a body model that has worked for 115 million years, like an evolutionary success story.”

A hunter’s past may hint at the future

Darwin’s study of sharks suggests that modern sharks rose to the top of prehistoric food chains early in their adaptive evolution, the researchers said. Now, scientists can scour similar environments worldwide for others, Care said.

“They must have been around before,” he said. “This thing had ancestors.”

Studying ancient ecosystems like this can help researchers understand how today’s species might respond to environmental change, Care added.

“This is where our modern world begins,” he said. “By looking at what happened in the past changes in climate and biodiversity, we can better understand what might happen next.”