Study explains how sauropods became the biggest animals on Earth

The sauropods included some of the biggest land animals ever to have lived, and their body shape is as fascinating as its size. Scientists have long wondered how their body shape evolved and how it contributed to the size of the animals.

Sauropods, which included Diplodocus, Apatosaurus and Brontosaurus, had extremely long necks, long tails and four thick legs. They also had strangely small heads in comparison to their bodies (although we wouldn’t have told them that to their faces).

Now, Dr. Karl Bates and a team from the University of Liverpool, UK, have used three-dimensional computer models to reconstructing the bodies. They examined how their size, shape and weight-distribution evolved over time, and found that changes in the body-plan coincided with major events in their evolutionary history, such as the rise of titanosaurs.

The researchers observed how sauropods evolved from creatures with a tail-heavy body shape to being very front-heavy. Their long necks were perhaps the most significant change, along with a shift from using four legs instead of two. The ancestral template that they evolved from had long tails, small chests and small forelimbs, a shape which the team assessed concentrated their weight close to the hip joint, helping them to balance while walking on their hind legs.

As they grew overall, their front features became enhanced and they began to walk on four legs.

Dr. Bates said: “As a result of devising these models we were able to ascertain that the relative size of sauropods’ necks increased gradually over time, leading to animals that were increasingly more front-heavy relative to their ancestors.”

A big send-off

During the last of dinosaurs’ three ages, the Cretaceous period, the evolution ended with the titanosaurs, which included the staggeringly huge Argentinosaurus and Dreadnoughtus.

Dr. Philip Mannion from Imperial College London, a collaborator in the research, said: “These innovations in body shape might have been key to the success of titanosaurs, which were the only sauropod dinosaurs to survive until the end-Cretaceous mass extinction, 66 million years ago.”

Dr. Vivian Allen of the Royal Veterinary College London, who also collaborated, cautioned: “What’s important to remember about studies like this is that there is a very high degree of uncertainty about exactly how these animals were put together. While we have good skeletons for many of them, it’s difficult to be sure how much meat there was around each of the bones. We have built this uncertainly into our models, ranging each body part from emaciated to borderline obesity, and even using these extremes we still find these solid, trending changes in body proportions over sauropod evolution.”

“We love the idea that, not being satisfied with being among the biggest creatures ever to exist, some sauropods allowed themselves to become obese.”

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Image credit: Thinkstock

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