Georges Cuvier (full name Jean Leopold Nicolas Frederic Cuvier, 1769-1832) originated a system of zoological classification that grouped animals according to the structures of their skeletons and organs. Cuvier extended his system to fossils; his reconstructions of the way extinct animals looked, based on their skeletal remains, greatly advanced the science of paleontology. Cuvier was a major figure in natural sciences research in the early 19th century, and was instrumental in establishing the fields of comparative anatomy and paleontology through his work in comparing living animals with fossils. He is well known for establishing extinction as a fact, being the most influential proponent of catastrophism in geology in the early 19th century. He established the fields of stratigraphy and comparative anatomy. He made the first thorough, published documentation of faunal succession in the fossil record, making extinction an accepted scientific phenomenon.