Babies! They're so cute! And one thing we find so endearing about our own offspring is how different they look from us as adults. Their legs and arms are stubbier, their heads are way bigger, and they just look like, well... like babies.
But while human babies have different proportions than adults of our species, that's not the case for all animals. Think of baby horses, for instance, on their feet and tottering around within a few hours birth. Though a foals is not exactly a perfect match for an adult, it's pretty darn close. And now new research shows that the largest dinosaurs that ever lived also hatched with similar proportions, shedding life on the different ways dinosaurs evolved to live and socialize.
New fossil analysis published today in the journal Science shows that hatchling titanosaurs came out of the egg with proportions very close to what they'd have when full grown. Researchers examined fossils of the titanosaur Rapetosaurus krausei, which was not the largest of the titanosaurs, the largest land animals that we know of, but could still grow to 50 feet (15 meters) in length and weigh about the same as a modern-day elephant. Baby R. krausei started out weighing only 7.5 pounds (3.4 kilograms) when hatched — the same as an average human baby.
This suggests, the authors propose, that R. krausei infants may have been more like today's horses than today's humans — cute, regardless, but relatively independent very early on in life.
The researchers studied the size and density of fossils of baby dinos who died, most likely from starvation, between the ages of 39 and 77 days. Using X-rays and microscopic analysis of bone structures, the scientists concluded that the titanosaurs grew with similar proportions throughout life. This isn't the case for other dinosaurs that lived in the Cretaceous period, like those in the theropod and ornithischian categories — Tyrannosaurus rex and velociraptors, and stegosaurs and triceratops, respectively.
No news on whether titanosaurs had adorable fat rolls and pinchable cheeks.