Cimolopterygidae

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Cimolopterygidae is an extinct family of early birds from the Late Cretaceous. They lived roughly 75 to 66 million years ago. Fossils attributed to cimolopterygids have been found in North America (the Frenchman Formation in Saskatchewan, the Lance Formation in Wyoming, the Fox Hills Formation in Colorado, and the Hell Creek Formation in Montana) and in Argentina (the Allen Formation in Rio Negro). Most specimens date to the end of the Maastrichtian, about 66 million years ago, but a much earlier species is known from Alberta’s Campanian Dinosaur Park Formation, around 75 million years ago. The family includes the genera Cimolopteryx, Ceramornis, and Lamarqueavis, with Cimolopteryx rara as the type species. They are part of the bird lineage known as Avialae/Ornithurae within the broader theropod-dinosaur group.