Oryzomys palustris

Karyotype: 2n = 56 and FN = 56. Autosomal complement: one small metacentric pair, and 26 acrocentric pairs (one very large and the remaining large to small decreasing in size). Sex chromosomes: X chromosome presented two different morphologies, a large acrocentric, and a large subtelocentric; Y, a small acrocentric (Gardner & Patton 1976; Benson & Gehlbach 1979, pp. 227, Fig. 1B; Haiduk et al. 1979). G-banding karyotype was performed by Haiduk et al. (1979) and Baker et al. (1983).

The karyotypes of O. couesi and O. palustris were very similar, but O. palustris exhibits a distinctly large acrocentric chromosome that was not present in O. couesi .