Cetiosaurids (Cetiosauridae): The cetiosaurs were a group of early sauropods. In fact, this group was an amalgamation of many different types of sauropods that had relatively simple vertebrae. Although some lived until the Late Jurassic period, the dinosaurs in this loose group retained some primitive features. Scientists believe that the cetiosaurids led the way, evolutionarily, for the more advanced forms of sauropods, such as the diplodocids, brachiosaurs, and camarasaurs. Some well preserved specimens of this group have recently been found in China, complete with skulls. These sauropods were distinguished by the lack of an opening in the jaw and five pelvic vertebrae, among other features. The cetiosaurids include the Middle Jurassic Shunosaurus, with a tail that ended in a club of bone; and the Late Jurassic Mamenchisaurus, with an extremely long neck containing 19 elongated vertebrae. The Mamenchisaurus was close to diplodocid line, but still retained a number of primitive characteristics that distinguished it from them.

Diplodocids (Diplodocidae): The diplodocids were a group of advanced sauropods living in the Late Jurassic period; they included some of the longest-known dinosaurs. The diplodocids had long, whip-like tails with at least 80 vertebrae, vertebrae with tall spines, small, long, and slender skulls with elongated muzzles, peg-like teeth only located in the front of the mouth, and nostrils on top of the head.

Brachiosaurids (Brachiosauridae): The brachi osaurids were another group of sauropods. These Jurassic period dinosaurs were much more massive than the diplodocids. Their most unique characteristic was front legs as long as—or even longer than—their rear legs. This, combined with their long necks, gave them a giraffe-like posture. In addition, the brachiosaurids had a relatively short tail comprised of about 50 small vertebrae, nostrils perched on a protrusion on top of the head, and a long neck with an average of 13 large vertebrae.

Camarasaurids (Camarasauridae): Depending on the classification system, the sauropods called camarasaurids can be listed as part of the brachiosaurids or placed in a group of their own. They were shorter and heavier than the diplodocids, with front and rear legs more similar in length. These Late Jurassic (to Late Cretaceous) period dinosaurs were the largest vegetarians had an average of 12 neck vertebrae; low, thick spines; vertebrae with extensive, deep cavities; large nostrils in front of the eyes; and large, spoon-like teeth set in a short, blunt skull. The Camarasaurus is the most common sauropod—and one of the smallest measuring 30 to 60 feet (9 to 18 meters) in the Morrison formation in the western United States. In fact, it is one of the only dinosaurs whose osteology—or the anatomy and structure of the bones—is completely known.