Jacques Armand Gauthier (born June 7, 1948, in New York City) is an American vertebrate paleontologist, comparative morphologist, and systematist, and one of the founders of the use of cladistics in biology.
His master's thesis, the content of which was published in 1982, is a classic work on the paleontology and phylogeny of the lizard clade Anguimorpha that remains a core reference for morphological research on Xenosauridae and Anguidae in particular.
His PhD thesis constituted the first major cladistic analysis of Diapsida, as well as arguing for the monophyly of the dinosaurs.
[4][5] In addition to his theoretical work on systematics and taxonomy, Gauthier continues to study the anatomy and relationships of diapsids, particularly lepidosaurs.
He is a principal investigator on the National Science Foundation-funded effort to reconstruct the phylogeny of lizards and snakes (Squamata) using gross anatomy and molecular structure, building on his earlier work in collaboration with Richard Estes and Kevin de Queiroz, which established the most widely accepted phylogeny of the group.