Lizards were a group of reptilian species, they were typically quadrupeds.
A large brown lizard species was used by the farmers in The Armada as a mount. These lizards were a similar size to horse and were used in a similar fashion, being fitted with a harness and saddles for riding. Cumin, the son of one of the farmers, complained to Wesley Crusher in 2365 about his chores on the farms, which included sleeping with the lizards when they were pregnant. (TNG comic: "Space Seeds")