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The 'Cuban Giant Owl' or 'Giant Cursorial Owl' ('''Ornimegalonyx oteroi''') is a giant, extinct species of owl, whose closest extant relative is the wood owl. It is believed to be the largest owl that ever existed. They lived on the island of Cuba. When the first specimen was described in the 1950s, the bones were so large that they were described as belonging to a bird in the family Phorusrhacidae. In 1961, Pierce Brodkorb reviewed the findings and placed them properly, with the owls. Remains have been abundant throughout the island, in cave deposits from the Late Pleistocene period (10,000s of years ago) and at least three nearly complete skeletons have been found.
Since then, it has been suggested that there were three subspecies of this bird (which were initially assumed to be distinct species). "Ornimegalonyx arredondoi" is a ''nomen nudum''; the name was proposed for this species before it was described but ''oteroi'' was eventually adopted by Oscar Arredondo (according to the rules of the ICZN, naming a species after one's self is not prohibited, but it is frowned upon as vain by the scientific community).
This owl is believed to have been at least 1 m (3.3 feet) tall and probably easily exceeded 9 kg (20 lb). It had very long legs for its size, but was bulky overall and probably short-tailed. The modern owl that most resembles the Giant Cursorial Owl is probably the dainty Burrowing Owl, the only surviving owl closely tied to the ground. This implies similar adaptations to the terrestrial lifestyle, but not a close phylogenetic relationship.
The legs and feet of the Giant Cursorial Owl appear to be very large and powerfully built. This supports the theory that they were strong runners, hence the title of cursorial. The keel of the sternum was reduced (if the keel were absent flight would have been impossible) and the owl may have been capable of short burst of flight. It is probable that, like a modern wild turkey, the owl only took flight when extremely pressed, more often choosing to run.
The Giant Cursorial Owl is believed to have preyed principally on large rodents (the size of modern nutria or capybara) and other medium-sized mammals (such as small ground sloths). It was probably an ambush predator that would pounch on unsuspecting prey with its crushing talons. Nothing about their life history is known, but based on their size, they probably laid a small clutch and had a long life-expectancy.