Scientists have developed 3D computer models of the bodies of the gigantic sauropod dinosaurs to analyse how their size, shape and weight-distribution evolved over time.
Sauropod dinosaurs include the largest land animals to have ever lived. Some of the more well-known sauropods include Diplodocus, Apatosaurus and Brontosaurus.
They are renowned for their extremely long necks, long tails as well as four thick, pillar-like legs and small heads in relation to their body.
To date, however, there have been only limited attempts to examine how this unique body-plan evolved and how it might be related to their gigantic body size.
Using 3D computer models, researchers from the University of Liverpool and Imperial College London, found evidence that changes in body shape coincided with major events in sauropod evolutionary history such as the rise of the titanosaurs.
The early dinosaurs that sauropods evolved from were small and walked on two legs, with long tails, small chests and small forelimbs.
The team estimated that this body shape concentrated their weight close to the hip joint, which would have helped them balance while walking bipedally on their hind legs.
As sauropods evolved they gradually altered both their size and shape from this ancestral template, becoming not only significantly larger and heavier, but also gaining a proportionally larger chest, forelimbs and in particular a dramatically larger neck.
The findings show that these changes altered sauropods' weight distribution 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.
The researchers found that these linked trends in size, body shape and weight distribution did not end with the evolution of fully quadrupedal sauropods.
In the Cretaceous period - the last of the three ages of the dinosaurs - many earlier sauropod groups dwindled.
In their place, a new and extremely large type of sauropod known as titanosaurs evolved, including the truly massive Argentinosaurus and Dreadnoughtus, among the largest known animals ever to have lived.
The computer models suggest that in addition to their size, the titanosaurs evolved the most extreme 'front heavy' body shape of all sauropods, as a result of their extremely long necks.
"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," said Karl Bates from University of Liverpool.
"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 from Imperial College London.
