Ornimegalonyx oteroi

Arredondo estimated the height of Ornimegalonyx to have been 1.1 m (3 ft 7 in) tall. It had very long legs for its size, but was bulky overall and probably short-tailed. Its body mass in life is initially estimated to have been approximately 30 kg (66 lb), but later studies suggest a mass of 9 to 13.5 kg (20 to 30 lb). The modern owl that most resembles the Cuban giant owl in proportions is probably the dainty and quite small 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 Cuban giant owl appear to be very large and powerfully built. This supports the theory that they were strong runners, hence the alternate name, cursorial. The keel of the sternum was reduced 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 females of this owl species were larger than the males.

The Cuban giant owl is believed to have preyed principally on large hutias, including Capromys, Geocapromys, and Macrocapromys (the latter being the size of a modern nutria or capybara) and the ground sloths Cubanocnus, Miocnus, Mesocnus, and Megalocnus, some of these sloths being roughly the size of an American black bear. It possibly fed on the Cuban flightless crane, Antigone cubensis. It was probably an ambush predator that would pounce on unsuspecting prey with its crushing talons.