Mega sea monster identified from ancient fossils

The oldest megapredatory pliosaur, Lorrainosaurus, in the ancient Middle Jurassic sea that covered what is to day northern France 170 million years ago. Artwork by: Joschua Knüppe (Germany).

The fossils of a 170-million-year-old ancient marine reptile from the age of dinosaurs have been identified as the oldest-known mega-predatory pliosaur.

The rare finding, in north-eastern France, was 40 years ago, but the latest discovery, adds to knowledge about the evolution of plesiosaurs.

Pliosaurs were ocean-dwelling reptiles closely related to the famous long-necked plesiosaurs, and had short necks and massive skulls. They appeared over 200 million years ago, but remained minor components of marine ecosystems until suddenly developing into enormous apex predators.

“Lorrainosaurus was one of the first truly huge pliosaurs. It gave rise to a dynasty of marine reptile mega-predators that ruled the oceans for around 80 million years.”

Sven Sachs, Naturkunde-Museum Bielefeld

The new study shows that this adaptive shift followed feeding niche differentiation and the global decline of other predatory marine reptiles over 170 million years ago.

An team of palaeontologists from Germany, Poland, Luxembourg and Sweden have now analysed the fossils, and identified them as a new pliosaur genus - Lorrainosaurus, which is named after the historical French region where it was found. They say Lorrainosaurus is the oldest, large-bodied pliosaur represented by an associated skeleton.

It had jaws over 1.3m long, with large conical teeth and a bulky torpedo-shaped body propelled by four flipper-like limbs. The giant reptile probably reached over 6m from snout to tail, and lived during the early Middle Jurassic period. Intriguingly, very little is known about plesiosaurs from that time, but pliosaurs were some of the most successful marine predators.

“Lorrainosaurus was one of the first truly huge pliosaurs. It gave rise to a dynasty of marine reptile mega-predators that ruled the oceans for around 80 million years,” explains Sven Sachs, a researcher at the Naturkunde-Museum Bielefeld in Germany, who led the study.

Daniel Madzia from the Institute of Paleobiology of the Polish Academy of Sciences, who co-led the study, said, “Our identification of Lorrainosaurus as one of the earliest mega-predatory pliosaurs demonstrates that these creatures emerged immediately after a landmark restructuring of marine predator ecosystems across the early-to-middle Jurassic boundary, some 175 to 171 million years ago. This event profoundly affected many marine reptile groups and brought mega-predatory pliosaurids to dominance over fish-like ichthyosaurs, ancient marine crocodile relatives, and other large-bodied predatory plesiosaurs.”

“Famous examples, such as pliosaurus and kronosaurus – some of the world’s largest pliosaurs – were absolutely enormous, with body-lengths exceeding 10 metres," says senior co-author Benjamin Kear, curator of Vertebrate Palaeontology and researcher in palaeontology at The Museum of Evolution, Uppsala University in Sweden.

Life-sized reconstruction of the head and jaws of the oldest megapredatory pliosaur, Lorrainosaurus

"They were ecological equivalents of today’s killer whales and would have eaten a range of prey including squid-like cephalopods, large fish and other marine reptiles. These have all been found as preserved gut contents.”

The recovered bones and teeth of Lorrainosaurus represent remnants of what was once a complete skeleton that decomposed and was dispersed across the ancient sea floor by currents and scavengers.

“The remains were unearthed in 1983 from a road cutting near Metz in Lorraine, north-eastern France," says co-author Ben Thuy, Curator at the Natural History Museum in Luxembourg. "Palaeontology enthusiasts from the Association Minéralogique et Paléontologique d’Hayange et des Environs recognised the significance of their discovery and donated the fossils to the Natural History Museum in Luxembourg.”

Other than a brief report published in 1994, the fossils of Lorrainosaurus remained obscure until this new study re-evaluated the finds. Lorrainosaurus indicates that the reign of gigantic mega-predatory pliosaurs must have commenced earlier than previously thought, and was locally responsive to major ecological changes affecting marine environments covering what is now western Europe during the early Middle Jurassic.

“Lorrainosaurus is thus a critical addition to our knowledge of ancient marine reptiles from a time in the age of dinosaurs that has as yet been incompletely understood”, says Kear.