the eastern fence lizard ("sceloporus undulatus") is a medium-sized species of lizard in the family phrynosomatidae. the species is found along forest edges, rock piles, and rotting logs or stumps in the eastern united states. it is sometimes referred to as the prairie lizard, fence swift, gray lizard, northern fence lizard or pine lizard. it is also referred to colloquially as the horn-billed lizard.