Babies of long-necked sauropod dinosaurs hatched from eggs no bigger than a soccer ball, and did not need parental care, a study of newly discovered fossil of a baby titanosaurian sauropod has found.
The research sheds the first light on the life of a young Rapetosaurus, a titanosaurian sauropod buried in the Upper Cretaceous Maevarano Formation of Madagascar.
Sauropod dinosaurs include the largest animals ever to walk on land, but they hatched from eggs no bigger than a soccer ball, researchers said.
The baby behemoths were active, capable of a wider array of manoeuvres than adult members of their species, and did not need parental care after hatching, they said.
The preserved partial skeleton was so small that its bones were originally mistaken for those of a fossil crocodile, said Kristi Curry Rogers of Macalester College in US, who led the research.
"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," Curry Rogers said.
"This is our first opportunity to explore the life of a sauropod just after hatching, at the earliest stage of its life," she said.
"These scientists employed several lines of evidence to investigate growth strategies in the smallest known post-hatching sauropod dinosaur," said Judy Skog, from the US National Science Foundation (NSF).
"It's intriguing that these animals developed quickly to function on their own, much like some birds and herding mammals of today," Skog said.
Researchers studied thin-sections of the tibia and used a high-powered CT scanner to get a closer look at the microstructures preserved inside the limb bones.
The detailed microscopic features of the Rapetosaurus bones revealed patterns similar to those of living animals and made it possible for the scientists to reconstruct the beginning of the dinosaur's post-hatching life.
"We looked at the preserved patterns of blood supply, growth cartilages at the ends of limb bones, and at bone remodelling," Curry Rogers said.
"These features indicate that Rapetosaurus grew as rapidly as a newborn mammal and was only a few weeks old when it died," she said.
The tiny titanosaur was mobile at hatching and less reliant on parental care than other animals. Baby sauropods like Rapetosaurus were somewhat like miniature adults, Curry Rogers said.
The team also observed microscopic zones deep within the bones. They proved similar to the hatching lines in today's reptiles, and to neonatal growth lines in extant mammals.
The zones indicate the time of hatching in Rapetosaurus, and allowed the scientists to estimate the weight of the newly hatched Rapetosaurus - around 3.5 kilogrammes.
The study was published in the journal Science.
