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Recently discovered remains of a female dinosaur are elucidating the ways in which these animals gave birth. According to a report published today in the journal Science, the fossil includes two complete eggs preserved inside the mother's body.
Tamaki Sato of the Canadian Museum of Nature in Ottawa and her colleagues analyzed dinosaur remains recovered from the Jiangxi province of China. The pelvic and leg fragments are from a dinosaur, which probably measured between 10 and 13 feet, belonging to a group known as the oviraptorosaurians. The larger egg is nearly 18 centimeters long and between six and eight centimeters wide, the team reports, but its similarity in size to the other egg suggests that the creature's two oviducts each produced an egg simultaneously. Modern female birds can only produce one egg at a time because they have only one ovary and oviduct. The laying of the eggs, however, appears to have been distinctly birdlike. Scientists had previously discovered dinosaur nests from the same time period that contained up to 15 eggs. That, together with the positioning of the eggs, suggests to the researchers that the dinosaurs would have repeated the egg-laying process a number of times to attain a full clutch just as modern birds do. Reptiles, in contrast, lay their entire clutch at once.
The results provide further evidence that dinosaurs share some aspects of reproductive behavior with birds, strengthening the belief that modern birds are their descendants. In addition, the find helps explain why the eggs in other oviraptorosaurian nests appeared to be arranged in pairs. The authors conclude that this configuration most likely arose because the eggs were laid nearly simultaneously and not because the parents manipulated the eggs.