The western order encompasses sharks commonly referred to as mackerel sharks. This group includes some of the most recognized shark species, such as great whites and shortfin mako sharks, along with lesser-known varieties like goblin sharks and megamouth sharks. The recent discovery of a 115-million-year-old giant shark in northern Australia indicates that oligarchs experimented with massive sizes around 15 million years earlier than previously believed, reigning at the top of the marine food chain alongside giant marine reptiles during the era of the dinosaurs.
In the ocean off the coast of Australia 115 million years ago, a gigantic 8m long predatory shark chases an unwary long-necked plesiosaur. Image credit: Polyanna von Knorring, Swedish Museum of Natural History.
Sharks are iconic predators in contemporary oceans, and their lineage dates back over 400 million years.
Nonetheless, the evolutionary journey of modern sharks initiated during the age of the dinosaurs, with the oldest known fossils appearing around 135 million years ago.
These early modern sharks, referred to as olipids, were relatively small, measuring roughly 1 meter in length, but evolved over time into colossal species like the renowned megalodon, which may have exceeded 17 meters, and the great white, known as the modern apex predator of the seas, measuring up to 6 meters.
Sharks possess cartilaginous skeletons, and their fossil record primarily consists of teeth, which are continuously shed as they eat.
This results in shark teeth being commonly found in sedimentary rocks on the ocean floor, alongside the remains of other species, such as fish and large marine reptiles, which dominated marine ecosystems during the time of the dinosaurs.
The rugged coastline around Darwin in northern Australia was once the mudbed of the ancient Tethyan sea, which extended from the southern reaches of Gondwana (now Australia) to the northern island archipelago of Laurasia (now Europe).
Fossils of sea creatures like plesiosaurs, ichthyosaurs, and large bony fish have been uncovered.
Most notably, several giant vertebrae were found, indicating the presence of an unexpected predator: the giant sheep shark.
The five recovered vertebrae were partially calcified, allowing for their preservation, and they closely resemble those of modern great white sharks.
However, while the vertebrae of an adult great white shark measure about 8 cm in diameter, the fossilized sheep shark vertebrae from Darwin exceeded 12 cm in diameter.
These vertebrae also exhibited unique morphological traits, enabling their classification within the Cardabiodontidae family, giant predatory sharks that have existed in the oceans for approximately 100 million years.
Significantly, the rhamniforms in Darwin were around 15 million years old and had already achieved the substantial body size characteristic of cardabiodontids.
“Our findings demonstrate that large body size is an ancient trait, with Australian storkids measuring between 6 to 8 meters long and weighing over 3 tonnes,” stated lead author Dr. Mohammad Bazzi from Stanford University and colleagues.
“This is comparable to some of the largest marine reptiles of their time and indicates that oligarchs entered the apex predator niche early in their adaptive evolution.”
“These sharks were substantial in size and inhabited shallow coastal waters,” added co-author Dr. Michael Syverson, a researcher at the Western Australian Museum.
“This provides significant insights into the workings of ancient food webs and underscores the value of Australia’s fossil remains in comprehending prehistoric life.”
“This discovery not only reshapes the evolutionary narrative of sharks but also enhances Australia’s global significance in paleontological studies.”
“With each fossil discovery, we refine our understanding of ancient oceans and the remarkable creatures that once ruled them.”
For more details on this discovery, refer to the new paper published in Communication Biology.
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M.Bazzi et al. 2025. Early giant amnioids mark the beginning of giant body sizes in the evolution of modern sharks. Commun. Biol. August 1499. doi: 10.1038/s42003-025-08930-y
Source: www.sci.news
