On bipedalism in skates and rays

Abstract

The anterior crurae of the pelvic fins in rajids are limb-like; this paper shows that these rays use the crurae for bipedal locomotion on the bottom at speeds around one-third of a disc length per second. It is suggested that this ‘walking’ pattern is employed to feed on prey within the substrate; sting rays (which feed in a different manner) do not possess such crurae. ‘Walking’ on a mud substrate leaves a characteristic track pattern as the crural tips dig in to propel the ray forwards; such tracks should be recognizeable in the fossil record.