The Silurians were distinguished by a number of crests which ran atop their head. When a group of Silurians evolved into Sea Devils, their crests became gill arches situated at the rear of the head through a process of exaptation. (PROSE: The Monster Vault [+]Loading...["The Monster Vault (novel)"])
The Silurians were distinguished by their crests atop their heads. (TV: Doctor Who and the Silurians [+]Loading...["Doctor Who and the Silurians (TV story)"])