Baby Rapetosaurus were only dog-sized a few weeks after hatching, but likely lived on their own. (Martin and K. Curry Rogers)

A rare look at a baby titanosaur suggests that these huge dinosaurs may have lived independently immediately after birth.

Long-necked titanosaurs were the largest animals ever known to walk the Earth (not to be confused with the largest animal ever known to swim the Earthor the most massive animal ever known to walk the Earth), and it seems their babies came out looking like miniature versions of Mom and Dad. Scientists led by Kristina Curry Rogers of Macalester College report on an infant of the titanosaur species Rapetosaurus krausei in a study published Thursday in Science.

But looking just like Mom and Pop is far from an indicator of close familial bonding.

“For sauropods, it doesn’t appear that they were very good parents — at least after their babies hatched,” Curry Rogers told the LA Times.


(K. Curry Rogers, M. Whitney, M. D'Emic, and B. Bagley)

Rapetosaurus krausei was puny when it hatched, at least compared with its parents. The 70-million-year-old specimen Curry Rogers studied weighed just 7.5 pounds at birth — lighter than most domestic cats (d'aw). The research team was able to turn back the clock and estimate the dinosaur's hatching weight by looking for something called the hatching line, which is a shift in bone growth that indicates when a baby left its egg.

By the time the baby krausei died — around 39 to 77 days later — it had packed on about 80 additional pounds. That's some impressive growth, but it's nothing compared with the thousands of pounds an adult probably weighed.


A hatchling-size dinosaur compared to the size of the dinosaur at its death. In contrast, an adult's femur is compared to an adult human. (K. Curry Rogers, M. Whitney, M. D'Emic, and B. Bagley)

But despite its tiny size, the baby dino's bones were proportioned similar to an adult's. That's something usually seen in animals that set out on their own not long after birth. While some sorts of animals — cats, dogs, humans and even some dinosaurs, for example — have big-headed, helpless babies, other species are born with the bodies they need to fight, flee and feed without the help of a parent.

The word for this immediate independence, by the way, is "precocial," which comes from the same root as "precocious," which I personally find delightful.

Brian Switek at National Geographic reports that the baby appeared to have been very active during its short life and that it was "ridiculously overengineered" with a body built to carry the massive weight it never lived to put on.

It might sound heartless for a plant-eating dinosaur to leave its babies wandering — especially during the age of predators like the T. rex — but having precocial young is a pretty good evolutionary strategy.

"Precocial young can avoid predation on their own, and there is a much smaller chance of the entire brood succumbing to predation at once," Curry Rogers told Reuters.

The strategy likely worked out for this fossilized dinosaur's mama — which may have had many successful young in her brood — but it was bad news for the baby Curry Rogers and her team studied. Based on the fossilized bones' thin layers of cartilage, they believe it died of starvation. That makes sense, because the site in Madagascar where the bones were found is thought to have been experiencing a severe drought during that period. It's hard out there for a baby titanosaur.

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