杏吧原创

It brings a whole new meaning to the word shellshock. A Jurassic turtle seems to have been squashed flat before it was fossilised 鈥� possibly because a giant dinosaur trod on it.

The marine turtle fossil was found in 2007 in Switzerland, as part of a project to study fossils that had been revealed by the construction of a highway. It dates from about 155 million years ago in the late Jurassic period. The dinosaurs were at their height then, and huge, long-necked sauropod dinosaurs dominated the land.

Most turtles from the time are found in marine sediments, but this one was on land. 鈥淚t鈥檚 like a tidal flat, where we mostly found dinosaur prints and tracks,鈥� says palaeontologist Christian Pu虉ntener, who was employed by the Republic and Canton of Jura in Switzerland to study the fossils. Finding the turtle there is significant, he says, because previously there was no hard evidence that Jurassic marine turtles ventured onto land.

The turtle was on its back, and it probably became stuck on the tidal flat and died there, says Pu虉ntener. It鈥檚 not clear what it was doing there. One possibility is that it came ashore to lay eggs, as marine turtles do today, but it is unclear if the animal was male and female, and if the tidal flat was a nursery there ought to be more turtle fossils.

A shell of its former self

However, the most striking thing about the turtle is the state of the fossil. Most of it is unusually flat. Seen from the side, a big chunk of it is visibly lower than the rest in the rocks. 鈥淭he main shell part is pushed down, relative to the posterior part,鈥� says Pu虉ntener. This suggests a heavy weight crushed much of the shell.

The rock layers in which it was found also contain a lot of dinosaur footprints, laid down on the tidal flat. The lowered part of the turtle fossil is 7.5 centimetres below the rest, which is about the depth of the dinosaur tracks. The implication is that a sauropod dinosaur trod on the turtle鈥檚 corpse after its death.

鈥淚t鈥檚 just a hypothesis,鈥� Pu虉ntener emphasises. There is no dinosaur footprint on or next to the turtle. 鈥淚f we had that, we would be sure about it.鈥�

However, Pu虉ntener says the turtle鈥檚 plastron, which covered its underbelly, is rotated relative to the main shell 鈥� perhaps as a result of twisting as the sauropod lifted its foot off. It may also be possible to identify tell-tale scratch marks on the fossil from trampling. 鈥淭hat would be further evidence,鈥� he says.