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.