William Daniel Conybeare FRS (7 June 1787 – 12 August 1857), dean of Llandaff, was an English geologist, palaeontologist and clergyman. He is probably best known for his ground-breaking work on marine reptile fossils in the 1820s, including important papers for the Geological Society of London on ichthyosaur anatomy and the first published scientific description of a plesiosaur.