How to raise a dinosaur? Tiny fossil may tell us
Scientists have stumbled on an extraordinary fossil of a baby dinosaur – a youngster so small you would have had to stoop to scratch its back.
If it had survived to adulthood, the infant would have grown into a behemoth the size of a fire truck. Even so, it emerged from the egg only as high as an adult human’s ankle. Then its growth spurt began. By the time it perished, at perhaps two months old, it had sprouted to knee height.
“It grew from this … Chihuahua-sized dinosaur at hatching to a golden retriever-sized dinosaur when it died in just a few weeks,” said Macalester College’s Kristi Curry Rogers, co-author of a study describing the specimen.
Never before have scientists found such a complete fossil of a very small baby sauropod, a member of the group of long-necked, plant-eating giants that includes the iconic and much-disputed Brontosaurus. Other young sauropods have been discovered, but all are either embryos, more mature than the new fossil or so piecemeal that they are impossible to identify.
By dying young, the miniature dinosaur provided a gift to scientists: its bones. Encoded in the fossil is a wealth of information about dinosaur development and parenting, which in this case was minimal.
Until now, scientists have been in the dark about sauropods from “elephant-sized (to) when they were embryos in the egg,” says paleobiologist Holly Woodward of the Oklahoma State University Center for Health Sciences, who was not associated with the new study. The new find “is the key fossil right now for understanding that period of a sauropod’s growth.”
Curry Rogers wasn’t even looking for baby dinosaurs when she found one. Instead she was prospecting for crocodiles and turtles in drawers of fossils excavated in Madagascar, but she kept finding tiny versions of the bones of a dinosaur she’d discovered more than a decade ago. That would be Rapetosaurus, a sauropod dinosaur that lived near the end of the Cretaceous.
The baby Rapetosaurus died young, probably of starvation, at one to two-and-a-half months old, Curry Rogers and her colleagues say in this week’s Science. But the researchers’ exhaustive examination of the itsy-bitsy bones suggest that before its death, this wee reptile could run, jump, even rear onto its hind legs – unlike adults, which were too big for such shenanigans.
The baby’s bones also show that it grew like a weed, confirming suspicions that sauropods shot up and out from the very beginning. That quick scaling-up may have helped keep them from turning into someone else’s lunch.
The 67-million-year-old fossil shows bone features typical of young animals that must fend for themselves even when newly hatched. While some types of dinosaurs did take tender care of their children, Rapetosaurus apparently wasn’t among them.
That makes sense, Curry Rogers said, given the evolutionary advantages of ignoring the kids, and the size difference between Junior and dear old Mom and Dad. It’s not obvious how “such large parents (could) take care of such tiny babies … without stepping on your offspring,” she said.
Findings from only one fossil may not apply to all sauropods, cautioned paleobiologist Martin Kundrát of Slovakia’s Comenius University, who was not involved with the analysis. But he tends to support the study’s conclusions. The research, he said, is important for understanding how sauropods’ lives unfurled.
“This is not the end of the story,” Curry Rogers agreed. All the same, “it’s nice to finally have a little look at what might’ve been going on with those dinosaurs.”