A visitor looks at the head of the Apatosaurio dinosaur fossil "Einstein", on display in Monterrey, Mexico.
Hollow neck bones made it possible for the largest of all dinosaurs to evolve necks longer than any other creature that has ever lived, researchers have suggested.
They said sauropods, the plant-eating dinosaurs, had by far the longest necks of any known animal, Fox News reported.
Their necks reached up to 50 feet in length, six times longer than that of the current world-record holder, the giraffe, and at least five times longer than those of any other animal that has lived on land.
Sauropods were really stupidly, absurdly oversized. They were 10 times bigger than elephants. In fact they were the size of walking whales, said researcher Michael Taylor, a vertebrate paleontologist at the University of Bristol in England.
To find out how sauropod necks could get so long, scientists analyzed other long-necked creatures and compared sauropod anatomy with that of the dinosaurs'' nearest living relatives, the birds and crocodilians.
In their study, Taylor and his colleagues found that the neck bones of sauropods possessed a number of traits that supported such long necks.
For instance, air often made up 60 percent of these animals'' necks, with some as light as birds'' bones, making it easier to support long chains of the bones. The muscles, tendons and ligaments were also positioned around these vertebrae in a way that helped maximize leverage, making neck movements more efficient.
In addition, the dinosaurs'' giant torsos and four-legged stances helped provide a stable platform for their necks. In contrast, giraffes have relatively small torsos, while ostriches have two-legged stances.
Sauropods also had plenty of neck vertebrae, up to 19. In contrast, nearly all mammals have no more than seven, from mice to whales to giraffes, limiting how long their necks can get. (The only exceptions among mammals are sloths and aquatic mammals known as sirenians, such as manatees.)
Moreover, while pterosaur Arambourgiania had a relatively giant head with long, spear-like jaws that it likely used to help capture prey, sauropods had small, light heads that were easy to support.
Scientists have proposed three theories to explain why sauropods evolved such long necks.
They suggested that some of the dinosaurs might have used their long necks to feed on high leaves, like giraffes do. Others may have used their necks to graze on large swaths of vegetation by sweeping the ground side to side like geese do. This helped them make the most out of every step, which would be a big deal for such heavy creatures.
Scientists have also suggested that long necks may have been sexually attractive, therefore driving the evolution of ever-longer necks; however, Taylor and his colleagues have found no evidence this was the case.
In the future, Taylor and Wedel plan to delve even deeper into the mysteries of sauropod necks.
For instance, Apatosaurus, formerly known as Brontosaurus, had "really sensationally strange neck vertebrae," Taylor said.
The scientists suspect the necks of Apatosaurus were used for "combat between males - fighting over women, of course."
Their study results have been published in the journal PeerJ.