Researchers excavated the 125-million-year old birds’ feathers, organs and bones from petrified lake-bottom mud in northeastern China. These birds, called Confuciusornis sanctus, were buried by the hundreds following catastrophic volcanic eruptions in the Mesozoic era.

Some C. sanctus fossils have long, fancy feathers and some don’t. Paleontologists have assumed the discrepancy in plumage was gender-based: the males were more decorated in order to attract and woo the drab-colored females, as in many modern bird species. But a new discovery, presented in a study in Nature Communications today, is the first actual proof.