Mesosaurid Swim Traces

Despite subaqueous fossils tracks of tetrapods being quite common in the fossil record, few studies discuss their classification and morphofunctional interpretation. Even with their simple morphology, some important information about the trackmakers can be retrieved from these tracks. Subaqueous traces were found in Brazil in the Irati Formation (Cisuralian, Permian), Paraná Basin, and described as Mesosaurichnium natans, related to Mesosauridae. The traces were produced in a shallow marine environment, whose substrate contained crustacean shells forming a thin layer. The mesosaurids produced the traces by swimming close to the bottom. The propulsion was provided by undulatory moves of the long tail, mainly for faster swimming. The feet could act as accessory and slower propellants, but provided more maneuverability.