Tetrapod means 4-legged, or, more precisely, 4-limbed. Dogs are tetrapods; so are humans and birds. Fish aren't tetrapods, because they lack arms or legs. However, snakes are considered tetrapods because their ancestors had four legs and were part of the tetrapod lineage.ogs are tetrapods; so are humans and birds. Fish aren't tetrapods, because they lack arms or legs. However, snakes are considered tetrapods because their ancestors had four legs and were part of the tetrapod lineage.