Long-Necked Dinosaurs Held Heads Horizontally

The group including the well-known Apatosaurus(formerly known as Brontosaurus) -- could not have kept their long necks in a vertical position, according to a new study.

At best, the dinosaurs would have needed to expend nearly half their energy just to hold their necks up, the study found. At worst, they would have passed out after lifting their heads at a 90-degree angle.

The study, published in the latest Royal Society Biology Letters, adds to an emerging consensus that sauropods held their necks -- up to 30 feet long -- in a horizontal position. In the future, museum exhibits, movies and books may reflect the change in their depictions of these enormous prehistoric animals.

Based on the new findings, it is believed that sauropods held their heads more like a horse than a giraffe.

"There is good evidence for a strong ligament that supported the neck horizontally at no energy cost to the animal," study author Roger Seymour told Discovery News. "Like horses, (sauropods) used their muscles to pull the neck down, not up."

Seymour, a professor of ecology and evolutionary biology at the University of Adelaide, performed a series of calculations to determine the metabolic rate and energy cost required for a sauropod to hold its head and neck aloft. He began by determining what the blood pressure would have been for the hefty dinosaurs if they had held their heads up.

"Blood pressure at a minimum can be calculated exactly from the vertical distance above the heart," he explained.

In Mamenchisaurus, for example, skeletal remains show its head, if the animal had reared, would've been more than 11 meters, or 36 feet, above its heart.

To generate high enough blood pressure to keep its head held high, the dinosaur's heart would have needed to have been five times thicker and 15 times heavier than that of an animal with more average blood pressure, according to the study.