The Astrapian sicklebill, also called the green breasted riflebird, is an unknown species of bird of paradise. It's known from a single specimen that was collected by Walter Rothschild in the late 1890s in the Bird’s Head Peninsula. The specimen is now kept in the American Museum of Natural History.
In 1930, Ornithologist Erwin Stresemann suggested in his scientific paper in Novitates Zoologicae, that the Astrapian sicklebill was not a new species. He proposed it was a hybrid between an Arfak astrapia and a black sicklebill, and has been assumed by the greater scientific community to be a hybrid ever since.
Various cryptozoologists, namely Karl Shuker, noted that the Astrapian sicklebill doesn't resemble either parent species at all. Shuker also pointed out that neither would likely breed with each other or would even be capable, as neither are genetically related, let alone in the same genus. No specimen or sighting of an Astrapian sicklebill has been seen since, although that doesn’t necessarily mean it’s extinct, as New Guinea’s vast interior is still uncharted.