An international team of paleontologists reported the first definite proof that the sex of early birds and dinosaurs can be determined by examination of a particular bone in the journal Nature Communications on Jan. 22, 2013.
The researchers examined the numerous fossils of Confuciusornis sanctus, a 125-million-year-old Mesozoic bird, in the Dalian Natural History Museum in northeastern China and found a difference in large bones that defines what sex the ancient bird was.
Just like modern birds, Confuciusornis sanctus females stored calcium in an extra part of the large bones called the medullary bone. The medullary cavity served as a source of calcium for egg shells.
Confuciusornis sanctus males were known to have elaborate plumage.
The discovery of the medullary bone also indicates females did not have the elaborate plumage that male Confuciusornis sanctus did.
The researchers also indicate that ancient birds began mating way before they were full grown.
Dinosaurs also began reproducing much earlier than reaching full size. Recent evidence suggests that a large majority of dinosaurs had some form of plumage.
The discovery anticipates the future ability to determine the sex of known fossil dinosaurs and new dinosaur finds. The sex of the vast majority of dinosaurs that are in museums or private collections is not known at present.
The research was reviewed at the Eureka Alert website the date of publication.
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