January 23, 2013
Researchers Find A Way To Determine The Sex Of Avian Dinosaurs
April Flowers for redOrbit.com - Your Universe Online
An international team of paleontologists, including Dr. Luis Chiappe, Director of the Natural History Museum of Los Angeles Country's Dinosaur Institute has discovered a definitive way to determine the sex of an avian dinosaur species.
The 125-million-year-old Mesozoic bird, Confuciusornis sanctus, had remarkable differences in plumage between specimens. Some had almost body length ornamental tail feathers, while others had none. Scientists have interpreted this difference in features as the earliest example of avian courtship. Until now, however, the idea that male Confuciusornis birds had the ornamental plumage was unproven. The research team studied hundreds of C. sanctus fossils unearthed from the bottom of ancient lake deposits in what is currently northeastern China. They found undisputed evidence of the gender difference: the medullary bone.
"Our discovery provides the first case of sex identification in an ancient bird, an animal closely related to dinosaurs, such as the famous Velociraptor," said Chiappe. "When people visit dinosaur exhibits, they often want to know if the skeletons are male or female. We have nicknames like Thomas and Sue, but of all the thousands of skeletons of dinosaurs or early birds found around the world, only the sex of a few has been determined."
Anusuya Chinsamy, the bone histologist on the team, says, "Just like modern hens, female Confuciusornis birds that lived 125 million years ago deposited this special bone inside their long bones, and then used it to make the calcium-rich eggshells." Such tissue is present for only a short period of time in reproductively active females, so finding such a sample in a specimen that lacked long feathers proved that those birds without the ornamental plumage were females.
"This now permits us to assess gender differences in growth and development of this Mesozoic bird," she said.
This discovery offers evidence that both early and modern female avian species essentially used the same physiological strategy to reproduce, however, it highlights the differences between the ancient and modern species age of sexual maturity as well.
"In human terms, knowing the sex of these specimens sheds light on when these early birds begin puberty," said Chiappe, "Now we know that early birds began reproducing way before they were full grown, a pattern that contrasts with what we know of living birds, which typically begin reproducing after they reach full body size."
The ancient birds began to reproduce before they were fully grown, like dinosaurs.
The specimens were excavated from rocks formed at the bottom of ancient lakes, found in forested environments surrounded by volcanoes. They were housed at the Dalian Natural History Museum in northeastern China. Large numbers of birds and other animals were killed by ancient catastrophes, thought to be related to volcanic events. Their bodies were buried deep in the lake mud that helped to minimize decay and preserve the organs, skeletons and feathers.
"This discovery is part of the big picture of understanding the early evolution of birds," Chiappe said, "and how living birds became what they are."
The findings of this study were recently published in Nature Communications.