Oecomys trinitatis (J. A. Allen & Chapman, 1893)

PATTON, JAMES L., DA SILVA, MARIA NAZARETH F. & MALCOLM, JAY R., 2000, Mammals Of The Rio Juruá And The Evolutionary And Ecological Diversification Of Amazonia, Bulletin of the American Museum of Natural History 2000 (244), pp. 1-306 : 131-132

Oecomys trinitatis

(Allen and Chapman, 1893)

TYPE LOCALITY: ‘‘Princestown, Trinidad’’ Princes Town, Trinidad and Tobago.

DESCRIPTION: This is the second largest species present in the Rio Jurua´, but it cannot be distinguished in most mensural characters from O. roberti (fig. 83). The head­and­body length averages 132 mm, and the tail (162 mm) is much longer than the body (123%), either unicolored dark brown, or only slightly paler below, with scale rows visible to the eye (16 scale rows per cm), clothed with short hairs (<2 scale rows long), and terminating in a slight pencil. The hind feet are short and broad, but not as broad as in O. superans ; the toes are typically darker than the metatarsal area. The dorsal coloration is dull brown with a slight reddish perfusion; a bright orange lateral line separates the dorsal and ventral colors, especially in the shoulder and chin regions; and the ventral fur is graybased with pale buff or white tips. The dorsal hairs appear distinctly thin, giving the pelage a sleeker appearance than in either O. roberti or O. superans , the latter which appears the most woolly, but the hair is of the same overall length. The skull (fig. 85) is somewhat narrower than that of other large species; zygomatic notches are shallow; supraorbital ledges are broad and strongly diverging; upper incisors are strongly opisthodont; an alisphenoid strut is present in three of five specimens, at least on one side; the tegmen tympani is usually in contact with squamosal; the subsquamosal foramen is open as often as occluded; the hamular process of the squamosal is more elongate and narrower than in other species; the incisive foramen is short, broadest at its midpoint, and thus ovoid in shape; the toothrows are intermediate in length between those of O. roberti and O. superans (MTRL 5.05; fig. 83); the posterior palatal pits are moderate in size and often divided; the mesopterygoid fossa is relatively narrow with an arched anterior border; the parapterygoid fossae are relatively shallow; and the bullae are very small and distinctly uninflated. Our samples are limited, but O. trinitatis cannot be distinguished from O. roberti by any cranial measurement, except the length of the incisive foramen (figs. 82 and 83).

SELECTED MEASUREMENTS: See table 29.

DISTRIBUTION AND HABITAT: This is apparently an uncommon but widely distributed species within the Rio Juruá basin. We found it at one or more localities within each of the four sampling regions (fig. 81), and on both sides of the river. Three were trapped on terra firme standardized lines (Penedo, locality 7; Barro Vermelho, locality 12; and Vira­Volta, locality 14); two were taken on the edge of flooded forest (Vira­volta, locality 14), and three were taken on várzea standardized lines (opposite Igarapé Porongaba, locality 2, and Barro Vermelho, locality 12). We caught the species on the ground (n = 3) as often as on canopy platforms (n = 3) or in lower branches 1.5 m off the ground (n = 2).

REPRODUCTION: All adults of both sexes were reproductive; and one juvenile was taken (at Penedo, locality 7, in August). One female was pregnant, with three embryos and two others had fresh placental scars these three were taken in both the late dry season (November) and late rainy season (May).

KARYOTYPE: 2n = 58, FN = 96 (fig. 91) We karyotyped four individuals, one each from localities 7 and 12 and two from locality 14. This complement is quite different from those of the other species of Oecomys reported here, with a much lower diploid number and proportionately larger autosomes. There are 16 pairs of large to small metacentric and submetacentric autosomes four pairs of large to medium subtelocentrics and eight pairs of medium to small acrocentrics. The X­chromosome is a large submetacentric, again the largest of the entire complement, and the Y­chromosome is a small acrocentric element.

SPECIMENS EXAMINED (n = 8): (2) 1m — MNFS 1250; (7) 1m — JLP 15425; (12) 1m 2f — JLP 15851, 15866–15867; (14) 1m, 2 — MNFS 1683, JUR 472, 497.