How to grow a giant dino

New dinosaur fossils from the Late Triassic of Argentina, around 237-201 million years ago, are described in a paper published online this week in Nature Ecology & Evolution. This specimen is among the earliest giant sauropods - 30 million years older than its titanosaur cousins - which changes our understanding of how this clade could grow to such immense sizes.

Long-necked and enormous, four-legged sauropods like Brachiosaurus and Diplodocus are among the most iconic of dinosaurs. Unlike such 50-tonne giants, however, the earliest examples of this group were small, two-legged creatures. To transition into towering behemoths, it had been thought that the development both of straight legs for support and of a continuous, rapid growth strategy were essential.

Cecilia Apaldetti and colleagues examined the fossils of the new dinosaur species Ingentia prima and the previously known species Lessemsaurus sauropoides, which are grouped together as ‘lessemsaurids’. These dinosaurs lived 237-201 million years ago - around 47 million years before Brachiosaurus and Diplodocus - in what is now Argentina, but was then the southeast corner of the supercontinent Pangaea.

Weighing in at an estimated 7-10 tonnes, the lessemsaurids had elongated necks and tails, although not so long as Diplodocus. Like later sauropods, lessemsaurids had bird-like air sacs - respiratory structures that may have been necessary to keep such large animals cool. Unlike their more recent counterparts, however, they stood on bent legs, and had bones that grew thick through accelerated bursts. These findings show that there is more than one way to ‘make’ a giant dinosaur, and that the last, iconic sauropods had the benefit of a long history of evolutionary innovation in this regard.

doi: 10.1038/s41559-018-0599-y

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