THEY might be ungainly on land, but in water it鈥檚 a different story 鈥� hippos glide gracefully along the river bed using their feet as punts. As they spend relatively long periods 鈥渋n flight鈥� between punts, their movements resemble those of astronauts in microgravity.
and Brittany Coughlin of West Chester University in Pennsylvania spent hours filming a pair of captive hippos at the Adventure Aquarium in Camden, New Jersey.
Contrary to popular belief, they saw no evidence that hippos actually swim. Instead, they spent most of their time 鈥減unting鈥� along the bottom, usually using one or both of their front feet as the punt. When they needed air, they launched themselves to the surface with their hind feet (Journal of Mammalogy, vol 90, p 675). Fish says that the weight and bone density of the hippos is an asset underwater because, coupled with the buoyancy of the water, it gives them momentum to spring forward.
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The findings also give a clue to how hippo-like creatures may have given rise to cetaceans, with whom hippos share a common ancestor. 鈥淔irst, they may have walked on the bottom and foraged,鈥� says Fish.
鈥淚t鈥檚 a compelling idea that bottom-walking might have preceded all-out swimming in other lineages,鈥� says John Hutchinson of the Royal Veterinary College in Hertfordshire, UK.