Cetiosauridae is a family of sauropods from the Middle Jurassic of Europe, roughly 168 to 161 million years ago, representing some of the earliest well-documented members of the sauropod lineage. Members retained solid (non-hollow) vertebrae, a primitive feature that sets them apart from later, more derived sauropods whose air-filled vertebrae helped reduce skeletal weight, and their overall build followed the standard sauropod pattern of a long neck and tail, a massive barrel-shaped body, and four sturdy, column-like legs supporting their great weight.
The type genus Cetiosaurus, whose name means "whale lizard" -- a reflection of how its enormous vertebrae were initially mistaken for those of a giant marine animal -- was recovered near Oxford, England, and remains one of the more completely known Middle Jurassic sauropods. The related genus Cetiosauriscus, from the Callovian stage of the Jurassic, was named for its similarity to Cetiosaurus. As sauropods with a comparatively primitive, solid-boned skeleton, cetiosaurids offer an important snapshot of what sauropod anatomy looked like before the weight-saving vertebral adaptations of later Jurassic giants like Diplodocus and Brachiosaurus became widespread.