Cetiosaurus conybeari was named by Melville (1849) [humerus (BMNH 28626) made type of Pelorosaurus, but the caudals are the type of the species C. conybeari.]. Its type specimen is BMNH 28626, a limb element (right humerus), and it is a 3D body fossil. Its type locality is Cuckfield Quarry, Tilgate, which is in a Valanginian/Hauterivian terrestrial sandstone in the Tunbridge Wells Sand Formation of the United Kingdom. It is the type species of Pelorosaurus.

It was recombined as Pelorosaurus conybeari by Mantell (1850), Mantell (1850), Mantell (1851), Gervais (1852), Mantell (1852), Mantell (1852), Pictet (1853), Owen (1859), Lydekker (1888), Newton (1889), Lydekker (1889), Woodward and Sherborn (1890), Lydekker (1893), Lydekker (1893), Van Den Broeck (1900), Sauvage (1900), Nopcsa (1901), Sauvage (1902), Huene (1927), Tatarinov (1964), Steel (1970), McIntosh (1990), Cheevely and Chapman (1992), Norman (1997), Blows (1998) and Upchurch et al. (2004); it was misspelled as Pelorosaurus conybearei by Mantell (1851) and Gervais (1859); it was considered a nomen vanum by Blows (1995); it was considered a nomen dubium by Naish and Martill (2001); it was misspelled as Pelorosaurus conybearei by Royo-Torres et al. (2006); it was synonymized objectively with Cetiosaurus brevis by Owen (1859), Blows (1998) and Naish and Martill (2007).