Harrison's Large-eared Giant Mastiff Bat

It is the largest member of its genus, and possesses the most robust skull. Males weigh between 31.5–45 g (1.11–1.59 oz), while females weigh between 26.8–45 g (0.95–1.59 oz). Its forearm length is 63.8–74 mm (2.51–2.91 in). Its total body length is 138–163 mm (5.4–6.4 in). Its tail is 30–48 mm (1.2–1.9 in) long; its hind foot is 11–16 mm (0.43–0.63 in) long; its ear is 34–46 mm (1.3–1.8 in). Its dental formula is 1.1.2.32.1.2.3, for a total of 30 teeth. Its ears project over its face, meeting in the middle over its nose. It has a minute tragus. Around its lips are loose folds of skin. Males have a gular gland located at the base of their throats. Its hind feet are broad, with long white hairs. It can be differentiated from other members of its genus based on its long cranium and exceptionally high braincase. Its fur is short and velvety. On its back, the fur is dark chocolate brown; it has a "distinct cream-coloured collar" around its neck. Fur on its ventral side is lighter than its back. The edges of its body and of its wing membranes have a thin, but distinct, band of white fur.

Its range includes Yemen, Djibouti, Ethiopia, and Kenya. It is most likely to occur in the eastern portion of Sub-Saharan Africa, also including Eritrea. Distribution modeling predicts that it prefers areas that receive at least 20 mm (0.79 in) of rain in the driest month, altitudes greater than 1,500 m (4,900 ft) above sea level, and locations with a total annual rainfall of less than 500 mm (20 in). They have been documented in woodlands, shrublands, montane grasslands, xeric grasslands, and thickets. During the day, they roost in mountain caves or lava caves.

It was described as a result of a taxonomic split in the large-eared free-tailed bat, Otomops martiensseni. It was split from O martiensseni based on morphological and genetic data. It has a genetic distance from O. martiensseni of 2.10%. The authors chose the species name "harrisoni" after the late mammalogist David L. Harrison. Of Harrison, they wrote: "[his] numerous publications on Afro-Arabian Chiroptera, in particular the Molossidae, have significantly improved our knowledge of this poorly known family."