In general, what characteristics determine if a dinosaur skeleton is a sauropod?
Paleontologists use several technical characteristics to determine if a dinosaur skeleton is that of a sauropod. In general, they look for the following:
1. Twelve or more neck (cervical) vertebrae.
2. Four or more sacral (between the hipbones) vertebrae (most modern reptiles have two; birds have over ten; and most modern mammals have three to five).
3. Massive, vertical limbs with long, solid bones.
4. Ilium (part of the pelvis bone) expanded to the back.
All sauropods have extra neck vertebrae, which is an evolutionary feature that developed at the expense of the back (dorsal) vertebrae. In addition, their skulls were weakly attached; thus the skull is often missing from the rest of the fossil skeleton. Additional skeletal characteristics are often used to classify fossils into groups and species, including the tail chevrons and the socket structure between the vertebrae.
What were the prosauropods?
The prosauropods (Prosauropoda) were some of the first dinosaurs to be discovered and described in the 1830s, which was even before the term dinosaur was coined to describe these huge reptiles. The name prosauropod, or precursor of the sauropods, is a misnomer, as the earliest known creatures were already too specialized to be the ancestors of the sauropods, but the name is still used today.
The prosauropods evolved during the late Triassic period some 230 million years ago, and they apparently disappeared at the end of the Early Jurassic period. Most prosauropods had blunt teeth, long forelimbs, and extremely large claws on the first finger of the forefoot (often called the thumb claw) ; most were semi-bipedal (walked on two legs). They were mostly herbivores, and only toward the Early Jurassic gained the huge size or special adaptations of the later herbivorous dinosaurs.
It is currently difficult to pin down the classification of the prosauropods. In certain classifications, saurischian dinosaurs were also divided into the suborder Sauropodomorpha, with another division Prosauropoda. Another classification suggests the Sauropodomorpha were divided into the Sauropoda, Prosauropoda, and Segnosauria. Still other classifications just list the prosauropods as an extinct offshoot of the saurischians.
What prosauropod fossils have been discovered?
In 1836, not long after the discovery of the first dinosaur fossils (although the term had not yet been coined), one of the earliest fossil prosauropods was found: a Thecodontosaurus; most of the fossil was later destroyed during bombings in World War II (since then, others have been discovered). A fossil Plateosaurus was found in 1834, thought to be the largest of its time and today considered the best-known and most extensively studied of all the prosauropods. Other prosauropod fossils have been discovered over the years, including the Azendohsaurus, Sellosaurus, Saturnalia, and Riojasaurus all from the Late Triassic period. From the Early Jurassic period, the most common prosauropods were the Massospondylus, Yunannosaurus, and Lufengosaurus.
What were some major groups of sauropods during the Jurassic?
There were several major groups of sauropods during the Jurassic period. They included the following:
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, evolutionary, 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, peglike teeth only located in the front of the mouth, and nostrils on top of the head.
Brachiosaurids (Brachiosauridae): The brachiosaurids 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.