Tisoa siphonalites dating 185 million years ago from the Upper Pliensbachian. The fossil burrow is made up of two tubes (the two rust-colored spots in the middle of the concretion) that can stretch several meters in length, making it the longest known underwater burrow. The burrow often serves as a nucleus for the growth of a calcareous concretion. Collection Jean-Philippe et Francois-Xavier Blouet, paleontologists.