Pregnant Teens Common Among Dinosaurs

Oct. 19, 2007 -- Dinosaurs probably did not enjoy many carefree teenage years, since most were parents before they reached adulthood, according to recently announced research.

The find puts dinosaurs on the list of animals that had teenage pregnancies. Others on the list include crocodiles, lizards and humans.

The discovery, announced in Austin at the Society of Vertebrate Paleontology's annual meeting, also suggests why evolution favors early births in these groups.

"Dinosaurs did pretty much what we do and what most other vertebrates do," explained co-presenter Andrew Lee. "If these species had waited until full size to reproduce, they would have had very few years in which to produce offspring."

Lee, a microanatomy instructor and post-doctoral fellow at Ohio University, and colleague Sarah Werning extracted bone tissue from three types of dinosaurs: Tyrannosaurus rex, Allosaurus and Tenontosaurus. The latter was a medium sized, plant-eating cousin of duck-billed dinos, while the former two were big carnivores, so the sampling represented a broad spectrum.

Three of the examined dinos possessed a special type of bone tissue called medullary that was used as temporary calcium storage before eggshells were made.

Lee explained to Discovery News that living birds possess this same tissue, which they form a few weeks before they are ready to create eggs. This means the analyzed dinosaurs were females that were ready to lay eggs just before they died. Their cause of death remains unknown.

Based on the growth stages of the dinosaurs, the scientists determined that T. rex was laying eggs by the age of 18, Allosaurus by age 10 and Tenontosaurus by the very young age of 8. Individuals within all three species would have reached full adult size between their 17th and 21st years. Their lifespan was from 25-30 years.