Nicolas Steno (; Latinized to Nicolaus Stenonis or Nicolaus Stenonius; 1 January 1638 – 25 November 1686 ) was a Danish scientist, a pioneer in both anatomy and geology who became a Catholic bishop in his later years. Steno was trained in the classical texts on science; however, by 1659 he seriously questioned accepted knowledge of the natural world. Importantly he questioned explanations for tear production, the idea that fossils grew in the ground and explanations of rock formation. His investigations and his subsequent conclusions on fossils and rock formation have led scholars to consider him one of the founders of modern stratigraphy and modern geology.