Fans of the Disney Channel's "Zoey 101," take heed. The pregnancy of 16-year-old star - and Britney sibling - Jamie Lynn Spears has some paleontological precedence.
New research, published in the Proceedings of the National Academy of Sciences, adds support for the idea that dinosaurs had babies starting in adolescence. For an animal that died young - roughly between ages 15 and 30 - such teenage pregnancies would have helped the species survive, scientists said.
Scientists studying the fossilized leg bones of adolescent female Allosaurus, Tenontosaurus, and Tyrannosaurus rex found medullary bone tissue, which, in modern-day birds, temporarily stores the calcium needed to make eggshells. The presence of this tissue in the three fossils suggests the creatures bore eggs before reaching adult size.
The notion that the tissue functioned in dinosaurs the way it does today in birds "is a pretty good inference," said researcher Andrew H. Lee, because no other animals seem to make this tissue. "It's a good first guess for now, but we have to do more research on it."
The presence of the bone in dinosaurs also reinforces the idea that birds and dinosaurs are evolutionary cousins.
Kristi Curry Rogers, a paleontologist at Macalester College in St. Paul, Minn., who co-authored one of the first studies on dinosaur sexual maturity, said the new research fits with her team's findings.
"They looked at a different signal of reproductive maturity than we did - we looked at tissue on the outside of bones and they looked inside - but found the same thing, that dinosaurs were still growing after reaching sexual maturity," she said. "Because it's a very different line of evidence, it strengthens the hypothesis."
Finding another evolutionary link between birds and dinosaurs wasn't necessarily his goal when Lee, then a University of California at Berkley graduate student, met Sarah Werning at a paleontology conference in 2005. Both were looking for growth patterns in dinosaur bones - he in the Allosaurus and she in the Tenontosaurus - and each independently stumbled upon the elusive medullary bone. Researchers had previously found the tissue in the Tyrannosaurus rex. The odds of researchers finding such tissue in three fossils were astronomical. Most dinosaurs probably reproduced once a year, with the tissue present for three to four weeks, and few ended up fossilized.
Because the two had already determined that their fossilized dinosaurs had died young, it was clear that they could reproduce years before reaching their adult size. Contemporary crocodiles also reproduce as adolescents.
"It reinforces just how complicated dinosaur biology is - it's not cut and dry," said Lee, now a post-doc instructor at Ohio University College of Osteopathic Medicine. "They're not crocodiles, and they're not birds: They're their own unique group of organisms."
Next, Lee said, he would like to determine the mechanism behind how birds form medullary bone.
"By understanding how it forms and works in living birds," he said, "we can understand how it may have worked in dinosaurs and possibly why it originated."
