33-foot-long 'Sea Monster' That 'Hunted All Animals' Found Surrounded by Ancient Crocodile Skulls and Teeth

Paleontologists at the Polish Academy of Sciences have found the partial remains of a 150 million-year-old sea monster—formally known as a pliosaurus—in a cornfield. The discovery was made near the village of Krzyżanowice in the Holy Cross Mountains of Poland.

"In Europe, they have been discovered only in a few countries, never before in Poland," Daniel Tyborowski from the Museum of the Earth of the Polish Academy of Sciences in Warsaw, Poland, said in a press release.

A study, published in the Proceedings of the Geologists' Association, describes the fossilized remains of a surprising assemblage of creatures from the Late Jurassic period, including the skull and teeth fragments from a large pliosaurus.

Dating reveals the fossils are between 145 and 163 million years old, when pliosaurs—a group of long, flippered reptiles—were top of the marine food chain.

These animals could swallow prey whole and reached lengths of 33-feet. To this day, they remain one of the largest predators to scour the world's oceans, according to the University of Oslo's Natural History Museum.

a pliosaur and a plesiosaur
An illustration of a pliosaur (bottom left) and a plesiosaur (top right). Szymon Zdziebłowski/Science in Poland

Pliosaurs existed in the Triassic and Jurassic Period and went extinct at the same time as the dinosaurs, 66 million years ago during the Cretaceous–Paleogene extinction event—as did another group of marine predators, the plesiosaurs, remains of which were also found at the Krzyżanowice site.

Bones from a long-necked species of plesiosaur belonging to the Elasmosauridae family and teeth from ancient crocodiles (or crocodylomorphs) were described in the study, along with the shell fragments of ancient turtles.

"Sea turtles ate large snails, while they themselves fell prey to large crocodiles," said Tyborowski. "We know this because we found teeth marks left by those reptiles on turtle shells. On the other hand, powerful pliosaurs hunted all animals whose fossils we discovered at this site."

How the discovery challenges ideas on Jurassic-era Europe

The diverse and eclectic selection of creatures challenges existing views on Jurassic-era Europe, which has previously been split into two main zones—a cooler Boreal/Sub-Boreal province and a warmer Mediterranean/Sub-Mediterranean province.

Large pliosaurids and long neck plesiosaurids tend to be found in the Boreal or Sub-Boreal ecosystems of places like Kimmeridge Clay in the United Kingdom and Svalbard Archipelago in Norway's Arctic. While crocodylomorphs and plesiochelyid turtles like those found in Krzyżanowice are usually found in Mediterranean or Sub-Mediterranean provinces, such as the Swiss Jura Mountains and Southern Germany.

In response to this surprising find, Tyborowski and his colleague Błażej Błażejowskib propose establishing a 'Matyja-Wierzbowski Line' named after two researchers of Late Jurassic paleobiogeography, Bronisław Andrzej Matyja and Andrzej Wierzbowski.

This line would represent a hypothetical barrier separating the ecosystems of the warmer Mediterranean climes to those of the harsher Boreal zones, where creatures from the Boreal zones (the pliosaurids and plesiosaurids) and creatures from the Mediterranean zones (the plesiochelyid turtles and crocodylomorphs) may meet and cohabit.

The line, they suggest, would extend from Dorset and Yorkshire in the United Kingdom through to Scandinavia, the Bohemian Massif in Central Europe and the Teisseyre-Tornquist Zone, a fossil plate boundary from the Baltic to the Black Sea.

"We hope that the next months and years will bring even richer material in the form of bones of large reptiles," said Tyborowski.