Little skates swim by rippling the pectoral disc, but they also walk. Two narrow lobes of the pelvic fins press against the bottom and move in alternation, producing a slow, deliberate gait that looks startlingly like the stepping of a small tetrapod.
A 2018 study traced the spinal circuitry behind it. The motor neurons controlling the pelvic lobes are specified by the same combination of regulatory genes, including Hox and related transcription factors, that patterns limb-controlling motor neurons in mice and other tetrapods. The implication is that the neural machinery for alternating limb movement predates the move onto land by a long way, and was already present in the common ancestor of skates and bony vertebrates.
The finding does not make skates ancestral to land animals. It relocates the origin of the circuit, showing it evolved in water and was later recruited for walking on ground.