Nyctomyini new tribe. Type genus—Nyctomys Saussure, 1860. Definition—Medium-sized tylomyine rodents with rich tawny to reddish-brown pelage, tail densely furred and noticeably penicillate; cranium with short, stocky rostrum and arched dorsal profile; jugal thin but a constant middle element of zygomatic arch; carotid circulation complete (Otonyctomys) or derived (most Nyctomys); basihyal with small, knobby entoglossal process; vertebral column with 13 thoracics and 6 lumbars (Carleton, 1980); M1 oval, anterocone narrow and undivided, M3 ovate, smaller than M2; two complete and five incomplete transverse palatal ridges (Carleton, 1980); accessory reproductive glands with two pairs of preputials, ampullaries loose and filiform, dorsal prostates strongly modified, anterior prostates and vesiculars absent (Voss and Linzey, 1981); glans penis with urethral process and dorsal papilla (Hooper and Musser, 1964a). Contents—Nyctomys Saussure, 1860; Otonyctomys Anthony, 1932.
Placed with thomasomyine group by Hershkovitz (1944, 1962, 1966c) based on its pentalophodont molars and short-wide palate. Numerous studies have supported removal of Nyctomys from thomasomyines proper and even questioned its placement within Sigmodontinae sensu stricto (Arata, 1964; Carleton, 1980; Haiduk et al., 1988; Hooper and Musser, 1964a; Steppan, 1995; Voss and Linzey, 1981). Phylogenetic interpretation of mitochondrial DNA sequences also suggest an ancient New World lineage, basal to Sigmodontinae or to Cricetinae-Sigmodontinae depending upon the trees generated (Engel et al., 1998).