Attempt to extend a found skeleton part. In this case it is a complex bone from a swan, called synsacrum, a skeletal structure which can only be seen in birds and other dinosaurs. The synsacrum is the section of the spine which, as a rigid structure, forms the roof of the pelvis.
Zeus fell in love with Leda and approached her in the form of a swan and impregnated her. But Leda’s husband Tyndareos also slept with her that night and she gave birth to two eggs with four children.