 This would imply that echidnas evolved from water-foraging ancestors that returned to living completely on the land, even though this put them in competition with marsupials.Further evidence of possible water-foraging ancestors can be found in some of the echidna's phenotypic traits as well.These traits include hydrodynamic streamlining, dorsally projecting hind limbs acting as rudders, and locomotion founded on hypertrophied humeral long-axis rotation, which provides a very efficient swimming stroke.