Oryzomys baroni Allen, 1897

Holotype. AMNH 11820/10112, a female specimen, collected by O. T. Baron, in 27.IV.1894 (Fig. 6).

Type condition. This specimen is preserved as skin and skull, both in good condition; the skin has a small area on the tail that has been torn and sown, and the pes are tied to each other and to the tail; the skull exhibit damaged nasolacrimal capsular projections as well as the proximal portion (maxillary and frontal) of the infra-orbital foramen.

Type material. The description of this species was based also on two additional specimens, AMNH 10111 and AMNH 11819: an old female, with molars and a sub-adult female, with molars only slightly worn, respectively.

Type locality. Malca, Cajabamba, alt. 8000 feet. The more appropriate designation would be Malca, Province Cajabamba, Region Cajamarca, Peru; alt 8,000 ft (circa 2,400m); geographical coordinates of this locality are 07°37’S, 78°03’W. The type locality is represented in figure 3.

Original description. This species was described on the Bulletin American Museum of Natural History, vol. 9, issue 8, 1897:117–118, as follows:

“Above yellowish brown, mixed with many blackish tipped hairs; sides paler and more grayish; below clear whitish gray, the hairs plumbeous at base, the basal portion slightly tinging the surface; fore limbs grayish brown to the base of the toes, which are lighter; lower portion of tarsus dusky, metapodials and toes dull soiled whitish; ears rather large, clothed thinly on both surfaces with short fine hairs, brown externally, slightly rufous internally; tail brown, nearly concolor, being barely lighter below, clothed with fine short hairs, too sparse to conceal the annulations. Mammae, i pectoral, i abdominal=4; only 3 functionally developed in the present specimen.

Skull—Cranial portion rather flat; facial portion broad, with very broad nasals; supraorbital and cranial ridges well developed, forming raised beads; palatal floor extending but slightly behind the last molar, but in other respects the skull and dentition are nearly as in typical Oryzomys, including tooth pattern.”

Original dimensions. Total length: 290 mm; head and body: 130 mm; tail: 160 mm; hindfoot: 30 mm. Ear from notch: 18 mm. Skull: Total length: 35 mm; basal length: 30 mm; zygomatic breadth: 17.5 mm; interorbital breadth: 11 mm; length of nasals: 13.5 mm; width of nasals at middle: 5. 5 mm; interparietal, 10 x 3 mm; length of interpterygoid fossa: 10.3 mm; palatine length, 15mm; length of anterior palatine foramina: 7 mm; upper molar series, 5.3 mm; diastema, 9 mm; length of lower jaw (from inner base of incisors to posterior border of condyle): 19 mm; from incisive tip to condyle: 22.3 mm; height of lower jaw at condyle: 8.6 mm; height of ramus at m1: 5 mm. Other craniodental measurements are in table 2.

Morphological description. Pelage soft, dense, lax, and long; yellowish wool and cover hairs and brown guard hairs; dorsal color yellowish cream, lightly grizzled with brown, resulting in grayish-yellow color; venter grayish; tail longer than head and body length, bicolored dorsoventrally, covered by very long hairs, with very small scales, with approximately 23 scales/cm; pes densely covered by long and white hairs, ungual tufts short and thin, some the same size as claw and others smaller, tufts white; plantar pads fleshy, including thenar and hypothenar; pinnae covered internally and externally with brown hairs with yellowish apex.

Skull moderately robust, with long and broad rostrum (approximately 38% of skull length [LN/ONL ratio]); zygomatic plate greatly projected anteriorly, not reaching beyond nasolacrimal capsule; rostral fossa moderately deep; greatly projected plate and moderately deep fossa, configuring a very deep and wide zygomatic notch; interorbital region convergent anteriorly, with supraorbital margins sharp and acute, forming small dorsolateral crests; zygomatic arches weakly divergent posteriorly, wider near the squamosal root; braincase small and delicate, elongated; braincase with temporal margins slightly squared, without crests; interparietal short and wide; frontosquamosal suture contiguous with fronto-parietal suture; alisphenoid strut absent; anastomotic channel present, configuring pattern 3 of carotid circulation (Voss 1988); parietals expanding over surface side of skull; incisive foramen long, wider medially, with anterior and posterior margins more acute, posterior margin leveled to the alveolus of M1; posterior margin of zygomatic plate situated anterior to the alveolus of M1; palate intermediate, with mesopterygoid fossa extending anteriorly between the maxillary bones but not between molars; palate with deep posterolateral palatal pits recessed in small and deep palatine depressions; palatal excrescencies absent; anterior border of mesopterygoid fossa rounded, roof of mesopterygoid fossa perforated by large vacuities, occupying the presphenoid and basisphenoid; auditory bulla, with short and wide stapedial process.

Upper incisors opisthodont; upper and lower molars with labial and lingual cusps arranged in opposite pairs; dental series significantly worn, hindering the full dental description.

Observation. Allen (1897) provided a superficial description of the external and cranio-dental morphology, and pointed to the close relationship of this species with O. xanthaeolus. He highlighted, however, that O. baroni specimens are much larger and their coloration is less yellowish than in O. xanthaeolus.