Paleontologists Discover Fossil Of Ancient Turtle Possibly Squashed By A Dinosaur

Photographs of the squashed shell. Püntener et al. 2019, Swiss Journal of Geosciences

The story begins in the Jura mountains (which the Jurassic period is named for) in Switzerland a mere 155 million years ago, when a turtle wandered into a tidal flat, somehow got stuck, died, and was subsequently squashed by a dinosaur. At least, that’s the prevailing hypothesis soon to be published in the Swiss Journal of Geosciences.

It was years later, in 2007, that the thuds and squeals of construction to build a highway through the mountains triggered the start of the team’s excavation of the turtle’s shell-shocked tale. The paleontologists removed rock that would have been discarded to build the highway and dubbed the follow-up research "Paléontologie A16" – after highway A16. In all, they found more than 15,000 dinosaur footprints and fossils from marine crocodiles and sea turtles. 

However, the team make special note of the turtle stepped on by a sauropod, describing it as "exceptional". By this, they mean the discovery of the turtle and not the survival prowess of the creature. The animal's unfortunate fate has provided researchers a window into an ancient world during the late Jurassic period.

"Fossils are generally scarce in these layers," the authors write in the study, "and only a few other vertebrate remains have been found in the laminites" – essentially sedimentary rock made up of fine layers. The discovery suggests the two creatures inhabited the same paleoenvironment at the same time.

The team can’t say for certain this event occurred as they describe, but they believe it did based on how far down the turtle fossil was pushed into the sediment – about 7.5 centimeters (3 inches), the same depth as the dinosaur footprints measured in the area. The rotation of the plastron, the flat bit that covered the animal's belly, could be due to "a slight horizontal friction of the dinosaur, either at the time of placing the foot onto the turtle shell or when taking it off."

 Comparison of a sauropod track with the taphonomic condition of the Jurassic turtle. Püntener et al. 2019, Swiss Journal of Geosciences

Stomping the turtle’s mistake home, the team note: “Examples of trampled vertebrates are rarely documented in the fossil record.”

They then name one of the few other creatures known to have this ignoble recognition: a flamingo associated with a camel track. The authors of that study suggest the already dead flamingo was stomped on by a camel that was crossing a lake bed near Puebla, Mexico, around 2 million years ago.

Preliminary findings suggest there are scratch marks on the flamingo’s bones, but confirmation of this has yet to be formalized. When it is, the team will likely take a close look at the turtle’s bones to see if they can corroborate a similar fate. 

Reconstruction of the hypothesis that a sauropod foot stepped on the turtle, thereby pushing the main shell further down. Püntener et al. 2019, Swiss Journal of Geosciences

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