Oryzomys xanthaeolus Thomas, 1894

Prado, Joyce Rodrigues Do & Percequillo, Alexandre Reis, 2016, Systematic studies of the genus Aegialomys Weksler, Percequillo and Voss, 2006 (Rodentia: Cricetidae: Sigmodontinae): Annotated catalogue of the types of the species-group taxa, Zootaxa 4144 (4), pp. 477-498 : 488-490

Oryzomys xanthaeolus Thomas, 1894

Holotype. BMNH 85.4.1.47, adult specimen, without information regarding sex, collected by J. Stolzmann, with no precise date of collection. There is no information on the original description about other specimens collected from the same or neighbor localities ( Fig. 5 ).

Type condition. Specimen preserved in skin and skull; the skin is in good condition and the skull is badly damaged, with basicranium, left ventral portion, and auditory bullae missing, right zygomatic arch broken, and left upper molar series missing, except for M1.

Type locality. “ Tumbez, N. Peru ”, as in the original description ( Thomas, 1894). Tumbez is a misspelling of Tumbes, the correct name for the river, locality and province of the NW Peru (see Stephens & Traylor, 1983). The more appropriate type locality would be “ Tumbes, Tumbes Province, North Peru ; geographical coordinates 03°34’S, 80°28’W”. The type locality is represented in figure 3.

Original description. the description was originally published on the Annals and Magazine of Natural History, ser. 6, vol. 14, in 1894 (p. 346–366), as follows:

“Size and general characters of O. galapagoensis, Waterh. , to which I had previously assigned it. Fur harsher and shorter than in that species, the hairs on the back about 10 or 11 millim. in length. General colour coarsely grizzled yellow and black, the mixture approximating to tawny olive of Ridgway. Cheeks and sides clearer yellow, or rather buff. Under surface white, the slate-coloured bases of the hairs scarcely showing through; line of demarcation on sides well defined. Eyes with a rather lighter ring surrounding them. Ears large, their substance apparently brown, thinly clothed with yellowish hairs. Hands and feet very thinly haired, almost naked, their few scattered hairs white; fifth hind toe (without claw) reaching to the middle of the first phalanx of the fourth. Tail very long, thinly haired, brown above and whitish below. Skull with a short broad muzzle, sharply edged and beaded supraorbital margins, and medium palatal foramina, about equal in length to the upper molar series.”

Original dimensions. Length of head and body: 121 mm; tail: 139 mm; foot: 30 mm; ear: 18.5 mm. Skullfront of interparietal to nasal tip: 28.3 mm; greatest breadth: 16mm; nasals: 12.7 x 4 mm; interorbital breadth: 5.1 mm; length of outer wall of interorbital foramen: 3.4 mm; palate length from henselion (henselion, accordingly to Thomas (1905: 193), “is the back of the alveolus of either of the median incisors, the point used and defined by Prof. Hensel in his craniological work”): 13.4 mm; diastema: 8 mm; palatal foramina 5.5 x 2.5; length of upper molar series: 5 mm; lower jaw: condyle to incisor-tip: 20 mm; height of ramus below: 4.4 mm. Additional craniodental measurements are provided in table 2.

Morphological description. Pelage soft, long, lax, dense and woolly; pale yellow wool and cover hairs and brown guard hairs; dorsal color yellowish cream, pale, weakly grizzled with brown medially, resulting in a pale yellow grayish general coloration; venter grayish, with gray based and white tipped hairs; tail longer than head and body length, conspicuously bicolor (dark gray above, unpigmented below); densely hairy, with scales very large, about 16 scales per cm; pes covered by white hairs and with short and sparse ungual tufts (approximately half size of claw), pads developed with thenar closest to hypothenar, surface rough; pinnae with very long hairs, more abundant externally, brown with golden apex and internally more golden than brown.

Skull moderately robust, with moderately long and broad rostrum; zygomatic plate weakly projected anteriorly, not reaching beyond nasolacrimal capsule; rostral fossa shallow; weakly projected plate and shallow fossa, configuring a shallow and narrow 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; fronto-squamosal 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; tegmen tympani large, not overlapped to squamosal; incisive foramen long, wider medially, with anterior and posterior margins rounded, posterior margin reaching anterocone of M1; posterior margin of zygomatic plate collinear to the alveolus of M1; palate with posterolateral palatal pits small, not recessed in palatine depressions.

Upper incisors opisthodont; upper molars with labial and lingual cusps arranged in opposite pairs; M1 with anteroloph connected to anterocone, parallel to it and separated from it by small anteroflexus; anterocone with weakly anteromedian flexus; paracone connected medially to protocone (and not to median mure) and to mesoloph more labially (defining a small and oblique mesofosset); mesoloph long, connected with median mure medially; mesoloph separated from metacone by long and deep metaflexus; posteroloph fused labially to metacone, defining a small posterofosset; M2 with short anteroloph; paracone connected medially to protocone (and not to median mure) and to mesoloph more labially (defining a small and oblique mesofosset); mesoloph long; posteroloph fused labially to metacone, defining a small posterofosset; M3 small, subtriangular; lower molars with labial and lingual cusps arranged in opposite pairs; m1 with weak anteromedian flexid; m1 and m2 with small lophulid emerging from the labial margin of entoconid (entolophulid or pseudo mesolophid) mesolophid on M1 and M2 small.

Observation. In 1884 (p. 453) Thomas identified two specimens from Tumbes (two skins) as Hesperomys (Oryzomys) galapagoensis , stating that this represent a record of this species in Peru. Ten years later, Thomas (1894) recognized this Tumbes sample as a new species, O. xanthaeolus , describing the external morphology of the species in detail, but providing a simplified description of the craniodental morphology. He compared the new species O. xanthaeolus with O. galapagoensis (informing that previously [in 1884] had assigned this specimen as galapagoensis ) and noted a clear association between the two species, but also described some differences between them, namely the more yellowish color in O. xanthaeolus , instead of the brownish hues of O. galapagoensis ; as well as the shorter fur and longer tail on O. xanthaeolus .

Figures

FIGURE 5. Dorsal, ventral and lateral views of the skull, and lateral view of the mandible of the specimen BMNH 85.4. 1.47, holotype of Oryzomys xanthaeolus Thomas, 1894 (ONL not available; Thomas, 1894 recorded the length of the “ front of interparietal to nasal tip ”: 28.3 mm).