WELLINGTON, New Zealand (AP) — In the age of the dinosaurs – before whales, white beluga whales and bus-sized buses. megalodon – monstrous shark roamed the waters of what is now northern Australia among the sea monsters of the Cretaceous period.
Researchers studying the huge vertebrae discovered on a beach near the city of Darwin say the creature is now the earliest known mega-predator of the modern shark lineage, predating the huge sharks previously found by 15 million years.
And it was huge. The ancestor of the current 6-meter (20-foot) great white shark was thought to have been about 8 meters (26 feet) long, say the authors of a paper published in the journal Communications Biology.
“Cardabiodontids were ancient, mega-predatory sharks that were very, very common in the Late Cretaceous, about 100 million years ago,” said Benjamin Keer, senior curator of paleobiology at the Swedish Museum of Natural History and one of the study's authors. “But this has pushed back the time frame from when we're going to find absolutely enormous cardabiodontids.”
Newly discovered fossils point to huge shark
Sharks have a 400-million-year history, but lamniformes, the ancestors of today's great white sharks, appear in the fossil record 135 million years ago. They were small at the time—probably only a meter long—which made it surprising for researchers to discover that lamniformes had already become giants 115 million years ago.
The vertebrae were found on a coastline near Darwin in Australia's far north and were once mud from the bottom of an ancient ocean that stretched from Gondwana – now Australia – to Laurasia, which is now Europe. This is a region rich in fossil evidence of prehistoric marine life, with long-necked plesiosaurs and ichthyosaurs among the creatures discovered so far.
The five vertebrae that kicked off the quest to estimate the size of their megashark owners were not a recent discovery, but an older one that had been somewhat overlooked, Cyr said. The fossils, discovered in the late 1980s and 1990s, measured 12 centimeters (4.7 inches) across and were kept in the museum for many years.
When studying ancient sharks, vertebrae are a prize for paleontologists. Sharks' skeletons are made of cartilage rather than bone, and their fossils mostly consist of the teeth that sharks shed throughout their lives.
“The importance of the vertebrae is that they tell us the size,” Kear said. “If you're trying to get it off the teeth, it's difficult. Are the teeth big and the bodies small? Are they big teeth with big bodies?”
The size of the ancient shark is still a mystery
Scientists have used mathematical formulas to estimate the size of extinct sharks such as megalodon, a massive predator that appeared later and may have reached 17 meters (56 feet) in length, Keir said. But the rarity of the vertebrae means questions about the size of ancient sharks are difficult to answer, he added.
An international research team has spent years testing different ways to estimate the size of Darwin's cardabiodontids, using fisheries data, CT scans and mathematical models, Kear said. Eventually, they came up with a likely depiction of the size and shape of the predator.
“To the world it would look like a modern basking shark, because that’s the beauty of it,” Cyr said. “This body model has lasted 115 million years and represents an evolutionary success story.”
A predator's past may hint at the future
Darwin's shark study showed that modern sharks rose early in their adaptive evolution to occupy the top of prehistoric food chains, researchers say. Scientists can now explore similar environments around the world in search of others, Kear said.
“They must have been somewhere before,” he said. “This thing had ancestors.”
Studying ancient ecosystems like this can help researchers understand how modern species might respond to environmental changes, Cyr added.
“Our modern world begins here,” he said. “By looking at what happened during past climate and biodiversity changes, we can better understand what might happen next.”
