Evidence for swimming in sauropods comes from fossil trackways that have occasionally been found to preserve only the forefeet (manus) impressions. Henderson showed that such trackways can be explained by sauropods with long forelimbs (such as macronarians) floating in relatively shallow water deep enough to keep the shorter hind legs free of the bottom, and using the front limbs to punt forward. However, due to their body proportions, floating sauropods would also have been very unstable and maladapted for extended periods in the water. This mode of aquatic locomotion, combined with its instability, led Henderson to refer to sauropods in water as "tipsy punters".