The Markoffian sea lizard was a type of lizard not native to Earth.
In 2366, when Q was stripped of his omnipotence and immortality, he thought of taking the form of a Markoffian sea lizard before deciding on taking the form of Human, as part of his punishment by the Q Continuum for his irresponsibility. (TNG: "Deja Q")
In the script, this species was identified as the Markoffian fire lizard.