Enantiornithean

The Enantiornithes (literally, "opposite birds", by which name they are popularly known), also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense). They were the most abundant and diverse avialan group known from the Mesozoic era and the first to spread across the globe. Almost all retained teeth and clawed fingers on each wing, but otherwise looked much like modern birds externally. Internally, they notably differed in the arrangement of shoulder bones, with a reversed or "opposite" ball-and-socket joint. In Enantiornithes, the scapula functions as a socket and the coracoid as a ball, whereas in modern birds, these bones function respectively as a ball and a socket.