A team of paleontologist has created 3D computer models of large dinosaurs to study how their size, weight distribution and body shape evolved through time. The study revealed that the evolution included the gradual variation in all three areas.

Led by Karl Bates from the University of Liverpool, the researchers reconstructed 3D models of sauropods, the most dominant group of massive herbivores during the Mesozoic era. Popular sauropods include Brontosaurus, Diplodocus and Giraffatitan.

Among the terrestrial vertebrates, the body plan and massive size of these herbivores are unparalleled. They had small heads, but very long necks and tails, with legs the size of pillars.

"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 Bates, from the university's Department of Musculoskeletal Biology.

They also discovered the dinosaurs' body shape variations happened almost at the same time when major evolutionary events took place, such as the rise of titanosaurs.

The sauropods evolved from a group of small dinosaurs that walked on two legs. These early ancestral dinosaurs had small forelimbs, small chests, but also had long tails. The team theorized that this ancestral body template had the weight concentrated near the hip joint. This helped the sauropods' ancestors walked using their two hind legs.

The 3D model approach revealed that the sauropods' evolution included the gradual alteration of both their body shape, weight distribution and size. They became heavier and bigger, especially on the chest part and forelimbs. They also developed larger necks compared to their ancestors.

This gradual body evolution also changed their weight distribution. They moved from being heavy on the tails to being heavy on the front area. They also shifted from walking on two hind legs to becoming four-legged dinosaurs.

In the research, published in the Royal Society Open Science journal on March 30, Bates and his colleagues discovered that the body shape, size and weight distribution evolutionary changes extended beyond the sauropods' evolution.

Many sauropod groups were lost in the Cretaceous period while a new sauropod type emerged. These new sauropods include the Dreadnoughtus and the Argentinosaurus, which are more massive than their ancestors.

Photo: Erik Drost | Flickr

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