Researchers have identified tell-tale signs of pregnancy in fossils from three young female dinosaurs, aged eight, 10 and 18 revealing that dinosaurs reached sexual maturity long before they were fully grown. The experts discovered calcium-rich bone tissue called medullary bone in cavities, thigh and shin bones from a meat-eating Allosaurus, a plant-eating Tenontosaurus and a Tyrannosaurus rex. Female birds deposit this type of tissue in marrow cavities in bones just before laying eggs, as a resource for making eggshells. Modern birds are descended from dinosaurs and likewise lay eggs.
'' 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,'' author Sarah Werning of University of California said.
The study published in the Proceedings of the National Academy of Sciences revealed that the prehistoric creatures reached sexual maturity long before they reached their maximum adult size.
In that respect, they were more akin to certain mammals, including humans, who are able to reproduce before they finish growing.
The dinosaur fossils contained medullar bone suggesting the creatures died before laying eggs, which could be a clue to the evolutionary reasons for the early sexual maturity.
Early pregnancies might have evolved to ensure the survival of the species, experts said.