Long necks were a key reason sauropods were able to get so big. Long necks let the animals reach foods other plant eaters couldn't, and meant the animals could stand in one place while practically inhaling food from a large swath of landscape. But as useful as they were, long necks had some big potential downsides. One of them was immense weight.
Notice the cavities and hollows in this bone, from the middle of the neck of a sauropod dinosaur. They were so striking to scientists that they named the animal Camarasaurus (cam-AIR-uh-SORE-us), which means "chambered reptile."
These hollows likely held air-filled sacs. Inclusion of air in the bones lightened sauropod necks by more than 50 percent; that weight reduction made holding and moving those necks possible.