Giant bones get archaeologists rethinking Triassic dinosaurs

Rodiano Bonacci
Luglio 10, 2018

But the earliest examples of this group were small, two-legged creatures.

With this discovery, researchers are now rethinking the evolution of dinosaurs, as they previously believed giant dinosaurs didn't exist until 25 million years later.

The remains of "Ingentia Prima" ('first giant') were found in Argentina, and are three times the size of previously discovered dinosaur species from the Triassic.

Cecilia Apaldetti of the University of San Juan said, 'Before this discovery, gigantism was considered to have emerged during the Jurassic period, approximately 180 million years ago, but Ingentia prima lived at the end of the Triassic, between 210 and 205 million years ago'.

"Although the origin of gigantism in sauropodomorphs [sauropods] was a pivotal stage in the history of dinosaurs, an incomplete fossil record obscures details of this crucial evolutionary change", the authors wrote in the study.

To turn into towering beasts, it was believed the development of straight legs for support and continuous, rapid growth were essential. Together, these dinosaurs belong to a sauropod subgroup known as the lessemsaurids, which lived between 237 and 201 million years ago (relatively soon after dinosaurs first appeared) in what is now Argentina but was then the southeast corner of the supercontinent Pangaea.

Dr Apaldetti said the climate would have been warm, with periodic monsoons. producing an African savannah style landscape, with plenty of shrubs on which Ingentia prima would feed.

For most dinosaurs, gigantism proved to be an evolutionary survival tool, especially among herbivores who could use their size as a form of defence against predators.

They were discovered in a dinosaur "nest" unearthed at a World Heritage site known for its fossils in Argentina's north western San Juan province.

The remains included shoulder blades, cervical vertebrae and bones from the forelimbs, feet and skull of the four dinosaurs.

Like their notorious descendants, they also had elongated necks and tails. These repiratory structures may have been necessary to keep such large animals cool.

The dinosaur's bone fragments displayed cyclical and seasonal growth, with a different kind of tissue to other sauropods, which allowed it to grow very quickly.

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