| Named By: | Friedrich von Huene in 1927 |
| Time Period: | Middle Jurassic, 166-164 Ma |
| Location: | England |
| Size: | Estimated to be about 15 meters long |
| Diet: | Herbivore |
| Fossil(s): | Partial post cranial skeletal remains including parts of the limbs, vertebrae and pelvis |
| Classification: | | Chordata | Reptilia | Dinosauria | Saurischia | Sauropoda | Eusauropoda | |
| Also known as: | | Ornithopsis leedsi | Cetiosauriscus leedsi | Cetiosaurus leedsi | |
Not to be confused with another sauropod dinosaur, Cetiosaurus.
Cetiosauriscus ( meaning "whale lizard like" i.e. "Cetiosaurus-like") is an extinct genus of sauropod dinosaur. It lived in the Callovian (Middle to Late Jurassic Period) of England (about 166 to 164 million years ago [mya]). Cetiosauriscus was a quadrupedal, herbivorous, saurischian, and was possibly the earliest diplodocid. It was named by Friedrich von Huene in 1927, for the species Cetiosaurus leedsi. Before 1993 it was shown that C. leedsi was not a Cetiosauriscus species, so that year Alan J. Charig sent a petition to the ICZN to designate C. stewarti as the type species. The remains include a series of vertebra, a hind leg, a partial sacrum, and a front leg. A potential additional specimen includes a diplodocid whiplash tail. Cetiosauriscus has, over time, been classified in Cetiosauridae, Diplodocidae, and Mamenchisauridae. It lived alongside Sarcolestes, Callovosaurus, and Lexovisaurus.