Under the feet of sauropods: a trampled coastal marine turtle from the Late Jurassic of Switzerland?

Abstract

Recent excavations from the “Paléontologie A16” project brought to light thousands of dinosaur footprints and numerous turtle remains from the Late Jurassic of Porrentruy (Swiss Jura Mountains). While most fossil turtles (Thalassochelydia) were found in marly layers that were deposited in a coastal marine paleoenvironment, the dinosaur (theropod and sauropod) tracks were found in laminites that were deposited in a tidal flat environment. Despite extensive exploration, very few body fossils were found in these dinosaur track-bearing laminites. On one occasion, a sub-complete turtle shell (Plesiochelys bigleri) was discovered within the laminites, embedded just beneath an important sauropod track level. The state of preservation of this specimen suggests that the turtle died on the tidal flat and was quickly buried. This is the first evidence that these turtles occasionally visited tidal flat paleoenvironments. Moreover, the particular configuration of the fossil turtle suggests that the shell was possibly trodden on by a large sauropod dinosaur.