A gigantic 8m long mega-predatory shark stalks an unwary long-necked plesiosaur in the seas off Australia 115 million years ago. Credit: Polyanna von Knorring, Swedish Museum of Natural History.
Around 115 million years ago, the seas off northern Australia were home to a gigantic shark mega-predator, ancestor of Jaws.
Fossils of this ancient mega-predator reveal that modern sharks experimented with enormous body sizes much earlier in their evolutionary history than previously suspected, and took the top place in oceanic food chains alongside massive marine reptiles during the Age of Dinosaurs.
This study, including researchers from Stanford University in the US, Lund University in Sweden, South Africa’s University of KwaZulu-Natal and the University of Oslo in Norway, presents a new interdisciplinary analysis to reconstruct size evolution in ancient sharks.
Sharks are iconic predators in the oceans today, and can trace their ancestry back over 400 million years.
However, the evolutionary history of modern shark lineages began during the Age of Dinosaurs, with the oldest known fossils dating from around 135 million years ago.
Known as lamniforms, these early modern sharks were small, possibly only about 1m long, but over time would give rise to giants, such as the famous ‘Megalodon’ that may have exceeded 17m in length, and the living Great White shark, which is an apex-predator in today’s oceans and tops the scales at around 6m.
115-million-year-old gigantic shark vertebrae. Credit: Mikael Siversson.
Sea Monsters
Sharks have cartilaginous skeletons. Therefore, their fossil record is mostly represented by teeth, which sharks shed continuously as they feed.
Shark teeth are subsequently very common in rocks that were laid down as sediment at the bottom of the sea, and occur alongside the teeth and bones of other animals, such as fishes and gigantic marine reptiles, which the dominant predators in most marine ecosystems during the Age of Dinosaurs.
The rocky coastline fringing the city of Darwin in far northern Australia was once mud from the floor of the ancient Tethys ocean, which stretched from the southern shores of Gondwana (now Australia) to the northern island archipelagos of Laurasia (now Europe).
The remains of sea monsters, including plesiosaurs (long-necked marine reptile resembling the popular image of the Loch Ness monster), ichthyosaurs (‘fish-lizards’), and large bony fish have all been found.
Yet most spectacularly, a handful of enormous vertebrae have turned up that reveal the presence of an unexpected predator — a gigantic lamniform shark.
115-million-year-old sea floor deposits exposed near Darwin in northern Australia. These rocks produce fossils of an ancient marine ecosystem that included the earliest modern shark mega-predator. Credit: Benjamin Kear.
Morphologically distinctive
The five recovered vertebrae were partially mineralised, which enabled their preservation, and are virtually identical to those of a modern Great White shark.
However, whereas adult Great Whites have vertebrae that are around 8cm in diameter, the vertebrae of the fossil lamniform from Darwin were over 12cm across.
They were also morphologically distinctive enough to identify them as belonging to a cardabiodontid — huge mega-predatory sharks that roamed the world’s oceans from about 100 million years ago.
Significantly, however, the Darwin lamniform is some 15 million years older and had already clearly achieved the hallmark massive body-size of cardabiodontids.
To accurately estimate the size of this earliest modern shark mega-predator, an international team of interdisciplinary scientists was assembled, including palaeontologists and tomographic from the USA Sweden, and Australia, and ichthyologists from South Africa and the USA The paper is published in the journal Communications Biology.
