Pregnant Teens Common Among Dinosaurs

Since smaller animals tend to reach sexual maturity earlier than larger animals, the smallest of the three dinosaurs studied, Tenontosaurus, was on a slightly faster track.

Florida State University paleontologist Gregory Erickson and his team recently came to similar conclusions using a different technique.

Instead of extracting bone tissue, Erickson and his colleagues counted growth rings in the bones of T. rex and other related dinosaurs, all of which had been found buried with brooding eggs.

Erickson and his group also concluded that T. rex gave birth before it reached full maturity.

"We now know that T. rex lived fast and died young," he said.

While birds are the modern descendants of dinosaurs, birds never give birth as teens. They finish growing and then may wait a year, or even longer, before reproducing.

Lee thinks several factors caused birds to change from their dino birthing ways.

"Flight is definitely part of the answer," he said. "Most birds need to be able to fly when they fledge, so they have to reach adult size."

Birds also now require a steep learning curve for survival, and the learning process takes time. Additionally, he said, "If birds matured early, their offspring might be born during the late summer or fall when food for growth is more scarce."

As for future humans losing their ability to produce as teens, Lee believes that's unlikely.

He said, "There is little benefit to delay sexual maturity in humans, so I can't imagine that selection might operate to delay sexual maturity before reaching adult size."