the ground and preventing the neck from pulling the body over. Aquatic capabilities In the 1980s, a number of studies suggested that Tanystropheus lacked the musculature to raise its neck above the ground, and that it was likely completely aquatic, swimming by undulating its body and tail side-to-side like a snake or crocodile. This interpretation has been disputed by later paleontologists, although Tanystropheus may have still spent a large portion of its life in shallow water. Renesto (2005) argued that Tanystropheus lacked clear adaptations for underwater swimming to the same degree as most other aquatic reptiles. The tail of Tanystropheus was compressed vertically (from top-to-bottom) at the base and thinned towards the tip, so it would not have been useful as a fin for lateral (side-to-side) movement. The long neck and short front limbs shifted the center of mass back to the long hind limbs, which would have made four-limbed swimming inefficient and unstable if that was the preferred form of locomotion. Renesto (2005) suggested that thrusting with only the hind limbs, as in swimming frogs, was an inefficient form of locomotion for a large animal such as Tanystropheus. A follow-up study by Renesto and Saller (2018) came to a different conclusion. They noted that, based on reconstructions of muscle mass, the hind limbs would have been quite flexible and powerful according to muscle correlations on the legs, pelvis, and tail vertebrae. Their proposal was that Tanystropheus, despite its apparent lack of adaptations for typical swimming styles, utilised a more unusual mode of underwater movement: extending the hind limbs forward and then simultaneously retracting them, creating a powerful 'jump' forward. Further support for this hypothesis is based on the ichnogenus (trackway fossil) Gwyneddichnium, which was likely created by small tanystropheids such as Tanytrachelos. Some Gwyneddichnium tracks seem to represent a succession of paired sprawling footprints from the hind limbs, without any hand prints. These tracks may have been created by the same form of movement which Renesto and Saller (2018) hypothesised as the preferred method of swimming in Tanystropheus. The idea that Tanystropheus evolved this form of swimming over much more efficient and specialised styles is evidence that it did not live an exclusively aquatic life, in contrast to longer-lasting marine reptiles such as ichthyosaurs or plesiosaurs.In the lifestyle interpretation of Renesto and Saller (2018), Tanystropheus was a shallow-water predator which used its long neck to stealthily approach schools of