Why Are Dinosaur Necks So Long?

By Joann Fan email: , Feb 25, 2013 12:07 PM EST

Dinosaurs were some of the largest living creatures that ever walked the earth, many with wildly impractical and impossible-sounding specs — er, physical qualities. The gargantuan sauropods (an order which includes the apatosaurus, which is commonly and inaccurately known as the brontosaurus), for instance, had necks that reached up to 50 feet in length, with a body approximately the size of a whale.

The sauropods were "really stupidly, absurdly over-sized," Michael Taylor, a vertebrate paleontologist at the University of Bristol in England, told Discovery News. "In our feeble, modern world, we're used to thinking of elephants as big, but sauropods reached 10 times the size elephants do. They were the size of walking whales."

The secret lies in their neck vertebrae, which scientists figured out by comparing sauropods to their closest living relatives, birds and crocodiles. Sauropod neck bones were made of 60 percent air, making them extremely light, the same way birds' bones are hollow. The tendons, muscles and ligaments in the sauropods' necks were also aligned in a way that could maximize leverage. They were also quadripedal, the enormous weight of their bodies set on four solid foundations to counterbalance the extreme lengths of their necks.

Head size also played a role. Sauropods had up to 19 neck vertebrae (most mammals have no more than seven), and had very small, light heads. They also had no cheeks in which to store food, and did not chew their food, swallowing the vegetation that made up their diet directly. "Sauropod heads are essentially all mouth," Mathew Wedel from the Western University of Healthy Sciences told LiveScience. "The jaw joint is at the very back of the skull, and they didn't have cheeks, so they came pretty close to having Pac Man-Cookie Monster flip-top heads," Wedel said.

Researchers also believe that sauropods probably breathed like birds, drawing air continuously into their lungs instead of having to exhale, which would have been extraordinarily difficult for organisms with such a long neck. The reasons they have such long necks in the first place can be attributed to the need to feed on high leaves, as giraffes do, and also to sweep their heads side to side to graze on vegetation on the ground, as geese do. This would maximize their energy expenditure for every step, considering how much effort it would take to move such an enormous body.

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