Before megalodon, researchers say a monstrous shark ruled ancient Australian seas

Ancient Mega-Shark Fossil Discovery Pushes Back Timeline of Ocean Predators

Scientists have identified the remains of a massive prehistoric shark that prowled the waters off northern Australia 115 million years ago, making it the earliest known mega-predator of the modern shark lineage. The discovery pushes back the timeline of gigantic sharks by 15 million years, surprising researchers who study the evolution of these ancient ocean predators.

The creature, belonging to the cardabiodontid family, is estimated to have measured approximately 8 meters (26 feet) in length—significantly larger than today’s great white sharks, which typically reach about 6 meters (20 feet). The finding challenges previous understanding of when sharks evolved to become apex predators.

“Cardabiodontids were ancient, mega-predatory sharks that are very common from the later part of the Cretaceous, after 100 million years ago,” explained Benjamin Kear, senior curator in paleobiology at the Swedish Museum of Natural History and one of the study’s authors. “But this has pushed the time envelope back of when we’re going to find absolutely enormous cardabiodontids.”

The breakthrough came from analyzing five vertebrae measuring 12 centimeters (4.7 inches) across that were discovered on a beach near Darwin in Australia’s Northern Territory during the late 1980s and 1990s. These specimens had been stored in a museum for decades before their significance was fully recognized.

The vertebrae originated from what was once the floor of an ancient ocean that stretched between the supercontinents of Gondwana (now Australia) and Laurasia (now Europe). This region has previously yielded other marine reptile fossils, including long-necked plesiosaurs and ichthyosaurs, making it a treasure trove for paleontologists studying Cretaceous marine ecosystems.

Vertebrae are particularly valuable discoveries for scientists studying ancient sharks. Unlike other vertebrates, sharks have skeletons made of cartilage rather than bone, which rarely fossilizes. The fossil record of sharks typically consists of teeth, which sharks continuously shed throughout their lives.

“The importance of vertebrae is they give us hints about size,” Kear noted. “If you’re trying to scale it from teeth, it’s difficult. Are the teeth big and the bodies small? Are they big teeth with big bodies?”

To determine the size of the Darwin cardabiodontids, researchers employed multiple methodologies including fisheries data, CT scans, and mathematical models. After years of testing different approaches, the team concluded that these prehistoric predators resembled modern sharks in their overall body shape.

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

The findings, published in the journal Communications Biology, suggest that modern sharks rose to dominance in marine food chains much earlier than previously thought. While lamniform sharks—ancestors of today’s great whites—first appear in the fossil record around 135 million years ago, they were believed to be much smaller, typically reaching only about one meter in length.

This discovery indicates that sharks evolved to become mega-predators relatively quickly in their evolutionary history. By comparison, the infamous megalodon, which may have reached lengths of 17 meters (56 feet), appeared much later in the fossil record.

The research opens new avenues for paleontologists to explore similar environments worldwide for evidence of even earlier giant sharks. “They must have been around before,” Kear suggested. “This thing had ancestors.”

Beyond satisfying scientific curiosity about prehistoric ocean ecosystems, studying these ancient predators could provide insights into how modern marine species might respond to environmental changes. As Kear emphasized, “This is where our modern world begins. By looking at what happened during past shifts in climate and biodiversity, we can get a better sense of what might come next.”

The discovery underscores Australia’s significance as a repository of prehistoric marine life and highlights how even long-stored museum specimens can yield groundbreaking scientific insights when examined with new perspectives and technologies.