Researchers have uncovered the fossils of a baby Rapetosaurus, a genus of long-necked sauropod dinosaurs, in the Upper Cretaceous Maevarano Formation of Madagascar. The findings, published in the journal Science on April 22, reveal that the baby Rapetosaurus weighed about 7.7 pounds (3.5 kilogrammes) and was just a few weeks old when it died.

Initially, the researchers mistook the partial skeleton for a crocodile fossil. However, further analysis of the remains’ preserved showed patterns of blood supply, cartilage growth at the ends of limb bones. More bone remodelling showed that it was actually a tiny sauropod that was already mobile and less reliant on its parents upon hatching.

“This baby’s limbs at birth were built for its later adult mass; as an infant, however, it weighed just a fraction of its future size,” says lead researcher Kristi Curry Rogers of Macalester College in St. Paul, Minnesota. “This is our first opportunity to explore the life of a sauropod just after hatching, at the earliest stage of its life.”


This is a comparison of an adult Rapetosaurus, a baby Rapetosaurus and a human. Credit: Kristi Curry Rogers

Although it was more capable of more manoeuvres than the older ones, this baby dinosaur was somewhat like a miniature version of fully-grown Rapetosaurus. This rapid developmental growth can be observed in many of today’s birds and mammals.


A baby Rapetosaurus stands alongside other young mammals of today for size comparison. Credit: Demetrios Vital

Moreover, microscopic findings suggest that the dinosaur’s hatching lines and neonatal growth lines are similar to the ones found in today’s reptiles and mammals, respectively.

The researchers suggest that the baby Rapetosaurus starved to death, most likely due to the extreme drought that occurred during its lifetime. Apparently, its cartilage growth plates resembled that of modified growth cartilages that occur among vertebrates as a result of starvation. “Between its hatching and death just a few weeks later,” adds Curry Rogers, “this baby Rapetosaurus fended for itself in a harsh and unforgiving environment.”

Long-necked sauropod dinosaurs are among the largest animals to have walked on land. Interestingly, their eggs are actually just the same size as a soccer ball.