The first fossil specimen was mistakenly described as a bird in the family Phorusrhacidae, in part because the bones were so large.

Remains have been found in cave deposits from the Late Pleistocene period (126,000 to 11,700 years ago).

[3] "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 oneself is not prohibited, but it is frowned upon as vain by the scientific community[citation needed]).

It is probable that, like a modern wild turkey, the owl only took flight when extremely pressed, more often choosing to run.

[4][9] 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 a black bear.