Dinosaur giants 'could not chew'

An inability to chew may be one reason why giant long-necked dinosaurs such as Brachiosaurus and Diplodocus got so big, scientists believe.

Because they swallowed plant material whole, they needed massive guts to allow enough time for it to be digested - and hence an enormous body.

Having no chewing jaws also meant the creatures could have small heads supported by long necks.

Although this gave them tiny brains in relation to their bodies, it offered the major advantage of gaining access to vegetation other animals could not reach.

Other factors, such as high growth rate, flexible metabolisms, and egg laying may also have helped to keep the creatures large, according to two experts writing in the journal Science.

The four-footed sauropod dinosaurs, characterised by their long necks and tails and huge bodies, were the largest animals ever to walk the Earth. They weighed up to 80 metric tons - 10 times more than an African elephant - and grew to lengths of more than 40 metres.

As well as being big, they were highly successful in evolutionary terms, dominating terrestrial ecosystems for more than 100 million years until the extinction of the dinosaurs 65 million years ago.

Environmental factors during the dinosaurs' reign cannot explain why the animals grew so vast, said Dr Martin Sander from the University of Bonn in Germany and Dr Marcus Clauss from the University of Zurich in Switzerland.

They pointed out that physical and chemical conditions at the time were probably less favourable for plant and animal life they are today, with much lower levels of oxygen in the atmosphere.

Variations in land mass, temperature, and atmospheric carbon dioxide were not accompanied by variations in sauropod body size, suggesting the key to their gigantism lay in their biology.

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