It was so named because its describer, Sir Richard Owen, supposed it was a marine creature, initially an extremely large crocodile, and did not recognise it for a land-dwelling dinosaur.

C. oxoniensis is estimated to have been about 16–18 metres (52–59 ft) long and to have weighed roughly 11 tonnes (12 short tons).

[3] The first fossils, vertebrae and limb elements, were discovered near Chipping Norton in the early nineteenth century and were reported upon by collector John Kingdon in a letter read on 3 June 1825 to the Geological Society; they were seen as possibly belonging to a whale or crocodile.

In 1841 biologist, comparative anatomist and palaeontologist Sir Richard Owen, named these as the genus Cetiosaurus, the year before he coined the term Dinosauria.

Between March 1869 and June 1870 Professor John Phillips, further investigating the site, in a layer dating from the Bathonian uncovered three skeletons and additional bone material.

[3] A century later, a new C. oxoniensis specimen (LCM G468.1968) called the "Rutland Dinosaur" was discovered on 19 June 1968 by the driver of an excavating vehicle.

Of the about two hundred bones in a cetiosaurus, it has preserved a nearly complete cervical series (2–14), most of the dorsal vertebrae, a small part of the sacrum and anterior caudals, the chevrons, the ilium, the right femur, and rib and limb fragments.

The model's vertebral column seen on display has fourteen cervicals, ten dorsals, five sacrals and about fifty caudals.

[3] In 1970 Rodney Steel renamed Cardiodon Owen 1841, based on a now lost tooth, into Cetiosaurus rugulosus, "the wrinkled one".

In 1874, Henri-Émile Sauvage named Cetiosaurus rigauxi based on a vertebra found by Edouard Edmond Joseph Rigaux at Le Portel, west of Boulogne-sur-Mer,[16] in layers dating from the Tithonian.

[18] In 1955, Albert-Félix de Lapparent named Cetiosaurus mogrebiensis based on three skeletons found in Morocco from the El Mers Formation dating to the Bathonian.

[22] Several fossil tracks discovered in 1997 and 2024 at two Oxfordshire, UK sites have been suggested to be Cetiosaurus footprints, though identification with a diplodocoid is also possible.

This conclusion, if correct, would cause considerable taxonomic instability, because the genus Pelorosaurus had since been based on its fossils, and recognized as a totally different kind of sauropod.

Its forearm was as long as the upper arm, unlike most other sauropods, resulting in a forelimb equalling the hindlimb in length.

In his original descriptions, Owen was unable to indicate any differences between Cetiosaurus and other sauropods for the simple reason these latter were not yet discovered.

Now that such relatives have been found, the uniqueness of Cetiosaurus oxoniensis and its status as a valid taxon must be proven by indicating its new derived traits or autapomorphies.

The vertebrae of the middle tail have a tongue-shaped process at the top of the front face of the vertebral body; this is an extension of the floor of the neural canal.

The lower process of the ilium, to which the pubic bone was attached, features on the outer surface of its base a triangular depression.

In the early 1850s, Gideon Mantell began to suspect that Cetiosaurus was a land animal as a result of his studies of Pelorosaurus.

Modern exact cladistic research has not resulted in a single clear outcome about the position of Cetiosaurus oxoniensis in the sauropod tree.

Sometimes a Cetiosauridae was recovered, a clade uniting Cetiosaurus oxoniensis with species as the Indian Barapasaurus, the South American Patagosaurus or the African Chebsaurus.

Cetiosaurus inhabited the London-Brabant Massif, a tectonic high that during this period formed an island landmass including parts of southern Britain and adjacent areas of northern France, the Netherlands, Belgium and western Germany, suggested to be comparable in size to Cuba with an area of around 100,000 square kilometres (39,000 sq mi).

A possible explanation for this is that the island remained ecologically connected to the much larger landmass comprising northern Britain (the Scottish Massif), the Fennoscandian Shield and the now submerged region in the North Sea between them.

[26] Other dinosaurs roughly contemporaneous to Cetiosaurus in the Bajocian-Bathonian of Britain include the large theropod dinosaurs Megalosaurus and Duriavenator (both belonging to Megalosauridae), the small tyrannosauroid Proceratosaurus and paravians (suggested to include dromaeosaurs and troodontids), and possible therizinosaurs,[36] as well as indeterminate heterodontosaurids, stegosaurs and ankylosaurs.

Paul considered Cetiosaurus a feeding generalist, eating at both a low and a medium-high level, in view of its moderately long neck and limb proportions.