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Dinosaur of the Day: Pregnant-teenager-o-saurus

As debates over sex education rumble along in America and elsewhere it’s nice to know that teenage pregnancies were also a problem for the last species to dominate Earth. And we can learn a lot from the youthful liaisons of the dinosaurs.

Researchers at UC Berkley looked at medullary bone in dinosaurs. This bone is found in the bone marrow cavity, where it provides calcium for egg shells in expectant females. Fossils containing this bone, combined with other studies of the skeletons, allowed the researchers to determine that three dinosaurs sampled – a Tenontosaurus, an Allosaurus, and a T. Rex – were fertile at 8, 10 and 18 years respectively (PNAS research abstract, live soon). This is important as it does not fit with a model that involves scaling up reptile growth to dinosaur sizes.


“What’s really cool about it is that now we can understand so much more about dinosaur biology – about their growth rates, their ages and sexual maturity, their size and life span, and compare it with modern animals,” says researcher Sarah Werning, of UC Berkeley (SF Chronicle).

Such early maturity could also be a survival strategy in a species that had a high adult mortality. Dinosaurs, it seemed, lived fast and died young.

“This is an exciting finding, because age at sexual maturity is related to so many things. It also shows that you can’t use reptiles as a model for dinosaur growth, as many scientists still do,” says Kevin Padian, who advised the paper authors and is a curator in UC Berkeley’s Museum of Paleontology (press release).

Werning and her co-author were pretty lucky to find the fossils, she explains in the Daily Telegraph,

It’s like this: think of all the women you see on the street. Some will be too young to reproduce, and some too old, but a lot will be of reproductive age. But the chance of meeting one who is ovulating is around 1/28 of the sexually mature women you meet. The chance of meeting a woman who is ovulating for the first time is much, much smaller.

With dinos, it’s even smaller chance – they only reproduced once a year. And maybe one in a million of those will get fossilised. And of those dinos that were fossilised, only so many are found and collected by museums, and so far not too many have been examined in this way (studying the bone tissues under a microscope), so it’s no surprise that we haven’t found too many of these pregnant dinos yet.

Image: “Cross-sections through the fossilized tibia or shinbone of a 120 million-year-old female Tenontosaurus skeleton, showing growth rings and medullary bone laid down in the marrow cavity just prior to egg laying.” / Sarah Werning/UC Berkeley & Andrew Lee/Ohio University; fossil courtesy of the Oklahoma Museum of Natural History


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