Oligoryzomys longicaudatus

Karyotype: 2n = 56 and FN = 66. Autosomal complement: six small metacentric and submetacentric pairs, and 21 acrocentric pairs (one large and the remaining medium to small decreasing in size). Sex chromosomes: X chromosome presented two different morphologies, a medium submetacentric, and a medium subtelocentric; Y chromosome presented two different morphologies, a small submetacentric, and a small subtelocentric (Gallardo & González 1977, pp. 313, Fig. 1A; Gallardo & Patterson 1985; Espinosa & Reig 1991; Palma et al. 2005; Belmar-Lucero et al. 2009; Palma & Rodríguez-Serrano 2017). Espinosa & Reig (1991) also reported a different fundamental number of 64 for a sample from Rio Negro, state of Argentina, according to the authors this difference was probably due to a pericentric inversion involving an autosomal pair. G-banding was also performed.