The saying goes that all babies are cute, but scientists now suggest one ginormous exception: the long-necked titanosaur.
The finding changes scientists' understanding of dinosaur family life, as the hatchlings that looked like adults almost from birth likely received minimal care from their parents, paleontologists wrote in a study published Thursday by the American Association for the Advancement of Science (AAAS).
"It's always seemed a bit weird to think of titanosaurs having much in the way of parental care," Thomas Holtz, a paleontologist at the University of Maryland, College Park, told Science magazine.
The hypothesis was untested, however, until paleontologist Kristina Curry Rogers found a familiar bone in a drawer full of crocodile fossils. She recognized one fossil as a miniature bone of a long-necked titanosaur, a species for which few hatchling samples had been found, Patrick Monahan wrote for Science.
"When we find sauropod bones, they are usually big," Dr. Curry Rogers said in news release from Macalester College in St. Paul, Minnesota. "Even juveniles can be bigger than cows. This is our first opportunity to explore the life of a sauropod just after hatching, at the earliest stage of life."
Her finding established evidence that these massive dinosaurs were precocial, meaning the hatchlings were quite self-sufficient from the time they left the egg. They looked like tiny versions of their parents from the moment they hatched, and they began to walk and live very much like their adult relatives almost at once.
"During the short interval between hatching and drought-related mortality, [the baby titanosaur studied] lived an active, precocial life," researchers wrote in the study.
This is not to say that the dinosaur would not have grown quickly. Adult titanosaurs were some of Earth's largest dinosaurs. Although the baby titanosaur was a little less than half the height of an average American human, the baby's parents approached 23 feet, more than three times a human's height and 10 times the baby's weight.
"The postcranial skeletons of very young Rapetosaurus were built to accommodate the massive adult sizes that they would eventually achieve," the authors wrote in the study.
The baby titanosaur may have been mechanically suited to life on its own, but that does not mean it was completely ready to forage for itself in the drought-ridden environment where this dinosaur was born. The young dinosaur's age was anywhere between 39 and 77 days old at the its death, but the skeleton's very thin cartilage suggests the beast died from lack of food.
"It's very exciting," Holly Woodward, a paleohistologist at Oklahoma State University, Tulsa, told Science. "There's direct evidence of starvation for the mode of death."
The finding cannot be applied to all dinosaurs, however, or even to all those in the long-necked giant family. Many other dinosaurs, including theropods and ornithischians, changed shape more dramatically between hatching and adulthood, according to a AAAS press release.