The ancient seafloor around what is now Darwin, Australia, once teemed with Cretaceous sea monsters — long-necked plesiosaurs, torpedo-shaped fish-lizards, and massive bony fish cruised the southern Tethys Ocean 115 million years ago. The seafloor sediments of this shallow shelf have preserved a rare mix of their remains, making it one of Australia’s few windows into early marine ecosystems.
Yet tucked within this assortment of marine reptiles and fish was evidence of an even larger predator — vertebrae from a shark whose bones were bigger than a great white’s and whose full body likely stretched 6 to 8 meters, about the length of a city bus. According to a new study published in Communications Biology, the find pushes the origin of mega-sharks back by roughly 15 million years.
How Early Lamniform Sharks Evolved
Sharks have been around for more than 400 million years, but the group that produced today’s great whites — the lamniforms — didn’t appear until the Age of Dinosaurs. The earliest lamniforms show up in rocks from about 135 million years ago as small, one-meter hunters, yet the group quickly diversified into a wide range of forms. Today, lamniforms include around 15 species, from coastal predators to deep-diving giants that exceed 10 meters in length.
Some lamniforms later grew into massive apex predators, including the 6-meter great white and the colossal Megalodon, which may have surpassed 17 meters. Tracing when that size shift began has been challenging, though, because sharks’ cartilaginous skeletons rarely fossilize. Their record is mostly teeth — not vertebrae or full skeletons — leaving only fragmentary clues about early body sizes. That makes the vertebrae from the Darwin Formation an especially valuable window into this chapter of shark evolution.
Read More: The Demon Shark: A New Shark Discovered Deep Off the Australian Coast
Reconstructing Australia’s Mega-Shark
To pinpoint the animal behind the oversized bones, the team analyzed five vertebral centra from the Darwin Formation. The fossils were unusually well preserved for shark cartilage, retaining enough mineralization to reveal their internal structure. Each centrum was enormous — up to 12.6 centimeters across, compared with roughly 8 centimeters in an adult great white — and carried the distinctive features of cardabiodontids, an extinct family of large lamniform sharks.
Gigantic shark vertebrae fossil from 115 million years ago, found in Australia.
(Image Credit: Mikael Siversson)
Estimating the shark’s full size required a different approach. The researchers assembled a large dataset of vertebral measurements from modern lamniforms — great whites, threshers, and other mackerel sharks — to understand how centrum diameter scales with body length. Applying those models to the Darwin fossils showed the sharks likely measured 6 to 8 meters long and weighed more than 3 tons, placing it among the dominant predators of the time.
The findings push the emergence of giant lamniforms much earlier than previously believed. Rather than evolving closer to 100 million years ago, these sharks had already begun exploring massive body sizes well before later giants like Cretoxyrhina or Megalodon entered the scene.
A New Look at Who Ruled Cretaceous Seas
The fossils suggest these early sharks were filling top-predator roles, competing with marine reptiles for space and prey along Australia’s shelf. That early ecological ambition shows that gigantism wasn’t a rare evolutionary experiment but part of a broader pattern in lamniform history, with giant body sizes evolving earlier and more often than once believed.
As more vertebrae emerge from sites like the Darwin Formation, the picture of who ruled Earth’s Cretaceous seas continues to shift.
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