Imperobator

MEANING: Powerful warrior

PERIOD: Late Cretaceous

CONTINENT: Antarctica

Imperobator is known only from a fossilized left foot, and is largely unknown, but it is likely an unenlagiine dromaeosaur. It was 2-3 m in body length, and probably covered in feathers. Imperobator is one of the very few non-avian theropods known from Antarctica, most likely having crossed over when it was still part of the southern continent of Gondwana.

Imperobator is from the Late Cretaceous. The Cretaceous is the third and final geological period of the Mesozoic Era, with the Late Cretaceous making up roughly the second half of it, lasting from about 100 to 66 million years ago. It was a time of significant evolutionary change, with dinosaurs reaching their greatest diversity before the mass extinction at the end of the Cretaceous.

The Cretaceous was a period with a relatively warm climate, though the Late Cretaceous experienced a global cooling trend, caused by falling levels of carbon dioxide in the atmosphere. The continents were nearing their present positions, but high sea levels flooded low-lying regions, turning Europe into an archipelago, and forming the Western Interior Seaway in North America. These seas were home to a variety of marine reptiles, including mosasaurs and plesiosaurs, while pterosaurs and birds shared the skies.

On land, dinosaurs continued to thrive and diversify during the Late Cretaceous, producing many of the most well-known goups, including tyrannosaurs, hadrosaurs, and pachycephalosaurs. Established Cretaceous dinosaur clades like the ceratopsians, ankylosaurs, and dromaeosaurs continued to flourish. Sauropod species consisted almost exclusively of titanosaurs, which seemed to be confined to the Southern Hemisphere for much of the Late Cretaceous. Flowering plants and grasses diversified and spread, becoming the dominant flora similar to what we see today.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene (K–Pg) extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. This event, likely triggered by an asteroid impact, is marked by the abrupt K–Pg boundary, a distinct geologic layer separating the Mesozoic and Cenozoic Eras. In its aftermath, mammals and avian dinosaurs rapidly diversified, becoming the dominant land animals of the Cenozoic Era.

Imperobator is an unenlagiid. Unenlagiidae is a family of small to medium-sized theropod dinosaurs within the larger group of dromaeosaurids - a group often associated with their birdlike anatomy and swift, predatory lifestyles. Unenlagiids were part of the Gondwanan radiation of dromaeosaurs, and they lived primarily in what is now South America during the Late Cretaceous Period. Like other dromaeosaurs, they had long, stiffened tails, sharp curved claws on their feet, and feathered bodies. However, unenlagiids also show features like elongated snouts and lightly built skulls, and in some cases, adaptations for increased agility suggesting semiaquatic lifestyles.

The distinct anatomy of unenlagiids compared to their northern cousins suggests that dromaeosaurs evolved in very different directions depending on where they lived.