In a world where paleontologists are used to making do with a handful of bones, the discovery of the most complete titanosaur skeleton ever found in Europe would be exciting enough. However, the really interesting thing about the newly described species Abditosaurus kuehnei is the mismatch between its immense size and its location in the Pyrenees.
Living on islands changes species, making some larger, some smaller and some lose the power to fly. In the last few million years before the asteroid strike, when Europe was a set of disconnected islands, the titanosaur family of sauropods took the second path, becoming smaller than their continental counterparts. At least that was what was believed, prior to the description of Abditosaurus’ 14 tonne (15.4 ton) bulk in Nature Ecology and Evolution.
"Titanosaurs from the Upper Cretaceous of Europe tend to be small or medium-sized due to their evolution in insular conditions," Dr Bernat Vila of Institut Català de Paleontologia Miquel Crusafont said in a statement. "It is a recurring phenomenon in the history of life on Earth, we have several examples worldwide in the fossil record of this evolutionary trend.”
By our standards, the European archipelago of the time included some large islands, including Ibero-Armorican, made up of modern-day Spain, Portugal, and much of France. To a titanosaur, however, this was still small enough to limit food resources, applying evolutionary pressure that shrunk these herbivorous dinosaurs.
Consequently, the discovery of the 17.5 meter (58 foot) Abditosaurus was a shock. However, with 53 pieces of its skeleton unearthed over a period of decades, including scattered limb and pelvic bones, 19 vertebrae, six ribs, and a few teeth, there is little doubt about its size. "We were really lucky, it is unusual to find such complete specimens in the Pyrenees due to its troubled geologic history," said co-author Dr Ángel Galobart.
The authors explain this puzzle by concluding Abditosaurus was a new arrival to Ibero-Armorican, crossing from Africa 70.6 million years ago when sea levels were briefly low. Its closest relative was the African Paralitian, followed by contemporary South American titanosaurs. It was probably not alone in having made the journey. "In the same site we have found eggshells of dinosaur species known to have inhabited Gondwana, the southernmost continent." said co-author Dr Albert Sellés.
As so often happens when island species are suddenly forced to compete with arrivals from another continent, things did not go well for the natives. The sudden change in Ibero-Armorican ’s inhabitants is known as the “Maastrichtian Dinosaur Turnover”.
The fact 68 years passed between the first Abditosaurus bone being found to the publication of its scientific description is testimony to how slowly things can move in paleontology, even when describing unusually important finds. The process was interrupted by long periods of neglect of the site and storms so large they forced excavation to stop. The interrupted nature of the work is commemorated for posterity in the genus name, which means “forgotten reptile”. The species name honors Walter Kühne, who found the first bones.