Imperobator

Imperobator ("powerful warrior") is a genus of paravian theropod, a group of large, three-toed carnivorous dinosaurs, that lived during the Maastrichtian stage of the Late Cretaceous period in what is now James Ross Island in Antarctica. Imperobator is unique, being one of two non-avian theropods known from Antarctica, crossing over to the landmass when it was part of Gondwana. The only known specimen was found in 2003 by an expedition launched by the University of California Museum of Paleontology and described initially as a dromaeosaur in 2007. However, later searches recovered more fossils from the site including teeth and skull bones. The fossils were later formally described as a new genus of giant paravian in 2019. Imperobator is one of the largest known paravians, with an estimated height of 2 metres (6.6 ft), making it of comparable size to the gigantic North American dromaeosaurs Utahraptor and Dakotaraptor. Its fossils lack the characteristic "sickle claw" on the second digit, excluding it from properly being considered a dromaeosaur. Imperobator's lack of complete remains has caused controversy over its classification. It was described as a basal paravian by Ely & Case (2019), but a later study recovered it as a basal dromaeosaur. It was discovered in the Cape Lamb Member strata of the Snow Hill Island Formation, which bears a variety of other fossils, many of them unique as they evolved in the isolation of Antarctica after the breakup of Gondwana. Imperobator coexisted with the ornithopod dinosaur Morrosaurus and bird Antarcticavis in addition to a menagerie of mosasaurs, plesiosaurs, and a pterosaur.