Scientists from the University of Liverpool have learned more about the evolution of sauropod dinosaurs and their oddly proportioned body structures thanks to the use of 3-D computer models.
Famous for their extremely long neck, long tail, relatively small head and four thick, pillar-like legs, sauropod dinosaurs such as Diplodocus, Apatosaurus and Brontosaurus are some of the largest land animals to have ever walked the Earth.
Little was known about how the dinosaurs evolved to obtain such a unique body shape, until now. By using computer models, researchers reconstructed the bodies of sauropod dinosaurs in 3-D, allowing them to analyze how the dinosaurs' size, shape and weight-distribution changed over time.
"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," explained Karl Bates, one of the study researchers from the university's Department of Musculoskeletal Biology.
It turns out that changes in body shape coincided with major events in sauropod evolutionary history. For example, the early dinosaurs that sauropods evolved from were small and walked on two legs, and they had long tails, small chests and small forelimbs. Based on this body shape, the researchers estimate that their weight was concentrated close to the hip joint, which would have helped them balance while walking bipedally on their hind legs. However, this all changed with the rise of titanosaurs, which were the largest of sauropod dinosaurs, measuring up to 130 feet long.
As sauropods began altering both their body size and shape, they not only grew significantly larger and heavier, but also gained a proportionally larger chest, forelimbs and, most distinguishably, a dramatically larger neck.
"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," said Philip Mannion, a researcher from the Imperial College London.
This, researchers say, demonstrates how sauropods' weight distribution changed as they grew in size, gradually shifting from being tail-heavy, two-legged animals to being front-heavy, four-legged animals, such as the large, fully quadrupedal Jurassic sauropods Diplodocus and Apatosaurus.
"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," added Vivian Allen, one of the study researchers from the Royal Veterinary College London. "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."
The findings were published in the March 30 issue of the journal Royal Society Open Science.
