Dinosaurs had pregnancies as early as age 8, far before they reached their maximum adult size, a new study finds.
Researchers at Ohio University and University of California at Berkeley have found medullary bone – the same tissue that allows birds to develop eggshells – in two new dinosaur specimens: the meat-eater Allosaurus and the plant-eater Tenontosaurus. It’s also been found in Tyrannosaurus rex.
The discovery allowed researchers to pinpoint the age of these pregnant dinosaurs, which were 8, 10 and 18. That suggests that the creatures reached sexual maturity earlier than previously thought, according to the scientists, who will publish their study Jan. 15 in the journal Proceedings of the National Academy of Sciences.
The scientists originally studied the bones, which come from different geologic periods, to learn more about dinosaur growth rates. Because researchers rarely find fossils of adult dinosaurs, some have speculated that the ancient beasts never stopped developing, said Andrew Lee, a postdoctoral student at the Ohio University College of Osteopathic Medicine who conducted the work as a graduate student at University of California at Berkeley with scientist Sarah Werning.
The new study suggests another explanation: Dinosaurs grew fast but only lived three to four years in adulthood. Offspring were probably precocious, like calves or foals, Lee said.
“We were lucky to find these female fossils,” Werning said. “Medullary bone is only around for three to four weeks in females who are reproductively mature, so you’d have to cut up a lot of dinosaur bones to have a good chance of finding this.”
The research also offers more evidence that dinosaurs were less like reptiles and more like birds. Though dinosaurs had offspring before adulthood, their early sexual maturity was more a function of their tremendous size than any anatomical similarity to crocodiles.
When they factored in the size of the dinosaurs, Lee and Werning found that the reptile model for sexual maturity predicted that the ancient beasts would have had offspring as late as age 218. “That’s clearly ridiculous,” Lee said. Research shows that most dinosaurs only lived until age 30, though long-necked creatures such as Brontosaurus may have reached 60.
“We hope this is the last nail in the coffin, but some scientists still cling to the notion that dinosaurs weren’t like birds,” Lee said.
The discovery also sheds new light on the evolution of birds. The presence of medullary tissue in these dinosaurs, which lived as long as 200 million years ago, shows that the reproductive strategies of modern birds have ancient origins.
Because birds have evolved to be much smaller than dinosaurs, however, their reproductive strategies and growth spans now bear no resemblance to those of T. rex. Birds grow to adulthood in only 40 days, but may take one to 10 years to reach sexual maturity. That’s relatively similar in other tiny critters such as shrews, Lee said.
NOW WE KNOW WHAT HAPPENED TO TREX! Their family VALUES declined until their civ generated so those nonarchosaurian mammals could take over! What a parallel warning we have for the modern era! Protect those family values! Or risk going the way of the T rex!
ahem. ok. politics OD recently.
It's interesting that they argue that T rex had a avian similar growth. That would imply a warm blooded metabolism. That runs rather contrary to the conclusions about the chasmosaurs in Horns and Beaks with the paper there on the subject. This always raises the possibility that endothermy is 'just' a theropod trait. However, there are not a lot of ectotherms out there that get nearly as big these days: they have a hard time competing with the endotherms. I have a hard time seeing that it would be much different back then in this respect.
Whoops. That's what I get for reading too fast:Tenontosaurus was included and seems to be implied that it grew the same way. hrm. What's that mean for ectothermy in dinos theory then?
Update #2: NatGeo has an article too.