Birds Lost Reproductive Baggage Before Taking Flight, Fossils Suggest

摘要

The ancient ancestors of today's birds lost an ovary in an adaptation that may have helped them take flight. At least, that's one interpretation of a study examining three 120 million-year-old fossils that contained preserved ovaries. Non-avian dinosaurs had two working ovaries, but almost all of today's birds-the kiwi being one exception-have only one, located on the left side. Researchers have long speculated that this loss served to lighten the birds' load for flight, but evidence for this notion has been scant.