Gigantic Dinosaurs Had to Grow Freakishly Fast 

By George Dvorsky on at

Titanosaurs were the largest land animals to ever appear on this planet, but even these lumbering beasts had humble beginnings. The discovery of a baby titanosaur fossil suggests that these dinosaurs were born with very adult-like features — and grew crazily fast.

Titanosaurs like Argentinosaurus, Apatosaurus (formerly known as Brontosaurus), and Rapetosaurus grew to enormous size. These four-legged, long-necked herbivores reached lengths of about 15 metres, and weighed nearly 90 tonnes, which is about the same weight as 25 adult elephants. The discovery of a baby Rapetosaurus krausei fossil shows that these animals hatched with adult-like proportions, suggesting they needed very little adult supervision.

A baby Rapetosaurus would have stood only knee-high to a human. (Image: Raul Martin and Kristina Curry Rogers).

The fossil dates back to between 66 to 70 million years ago, and it was discovered in Madagascar. The tiny titanosaur was about 35cm long when it died, apparently of starvation. Analysis by Macalester College palaeontologist Kristina Curry Rogers and colleagues shows that this dinosaur, which was about 40 to 77 days old when it died, exhibited very adult-like features even at this early stage in its life.

This discovery affirms the ongoing theory that titanosaurs were “precocial” vertebrates, meaning they were able to move independently immediately after birth, and featuring a greater range of physical motion than adults. Soon after hatching, these creatures were able to stand on all-fours and begin independent living. They likely required very little parental oversight. This runs in contrast to a number of other dinosaurs, including theropods and ornithischians, for whom parental care was paramount.

Rapetosaurus krausei also grew incredibly fast. This specimen weighed about 3.4 kilos when it hatched, but just several weeks later it reached 40 kilos. As Moines University palaeontologist Sarah Werning told National Geographic, “That’s like going from Chihuahua to a great Dane in six weeks”.

It's a very cool discovery. One that shows just how complex and varied these ancient creatures really were, while also painting an extraordinary picture of what early life was like for some dinosaurs. [Science AAAS]