Aside from being the largest marine turtle species ever discovered in Europe, and one of the largest worldwide, the discovery of Leviathanochelys aenigmatica suggests that gigantism in marine turtles was acquired independently, by different lineages over time.
Leviathanochelys aenigmatica lived during the Campanian age of the Late Cretaceous epoch, some 78 million years ago.
“Marine turtles were common in the subtropical Upper Cretaceous epi-continental seas that once washed the coasts of the ancient European archipelago,” said Universitat Autònoma de Barcelona paleontologist Albert Sellés and his colleagues.
“But unlike its contemporaneous faunas from North America, in Europe no species surpassed the 1.5 m shell-length.”
With an estimated body length of up to 3.7 m, Leviathanochelys aenigmatica represents the largest marine turtle to have been found in Europe to date.
The largest known marine turtles such as the extinct genus Archelon, which grew to sizes of 4.6 m long and weighed up to 3.2 tons, lived in the seas surrounding the North American continent towards the end of the Cretaceous period.
The fossilized remains of Leviathanochelys aenigmatica were found at the locality of Cal Torrades in Spain.
They consisted of a fragmented but almost complete pelvis and parts of the upper shell (carapace).
“The specimen possesses a distinctive prominence of bone that protrudes forwards from the front of the pelvis,” the paleontologists said.
“This feature differs to other marine turtles, and indicates that Leviathanochelys aenigmatica represents a new taxon (group) of ancient marine turtles.”
“This protrusion may have related to the respiratory system.”
The researchers estimate that the maximum width of Leviathanochelys aenigmatica’s pelvis was 88.9 cm, which is slightly larger than the biggest estimates for Archelon’s best known specimen (81 cm wide).
The length of the pelvis from front to back was estimated to be 39.5 cm, slightly smaller than that of Archelon (46 cm long).
“The discovery of the new gigantic and bizarre chelonioid Leviathanochelys aenigmatica from the Middle Campanian marine deposits of the Southern Pyrenees, which rivals in size to Archelon, sheds a light on the diversity of marine turtles and on how the phenomenon of gigantism in these groups was also occurring in Europe,” the authors said.
“Despite the scarcity and fragmentary nature of the individual, the new evidence not only increases the taxonomic diversity of the Late Cretaceous marine turtle biota in Europe, but also opens a new line of exploration and raises new questions, in order to solve the evolutionary mechanisms and ecological pressures that could have favored the independent evolution of colossal (over 2.5 m in shell length) marine turtles in multiple lineages, especially during the Late Cretaceous epoch.”
The findings are published in the journal Scientific Reports.
O. Castillo-Visa et al. 2022. A gigantic bizarre marine turtle (Testudines: Chelonioidea) from the Middle Campanian (Late Cretaceous) of South-western Europe. Sci Rep 12, 18322; doi: 10.1038/s41598-022-22619-w