Tree-rice rats are small to medium-sized cricetines of the genus Oryzomys (family Muridae). The general characteristics of the subgenus Oecomys are common to Oryzomys and a number of other genera that together form the theoretical zomyine group of the subfamily Cricetinae (family Muridae). The ranges of the two species are coextensive in Panama, the Rfo Orinoco Basin of Colombia and Venezuela, and the Amazon region.
It is based on an eastern Brazilian representative of the larger species of subgenus Oecomys. The next member of the species, collected in western Ecuador, was described by Thomas in 1900 as Rhipidomys dryas. In 1906, Thomas discovered the essential oryzomyine characters of the small tree rice rats which he assigned to Rhipidomys.
Based on the available data, the systematic position of Hesperomys simplex cannot be determined more precisely.
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RIGHT UPPER MOLARS LEFT LOWER MOLARS
FIRST UPPER MOLAR
BUCCAL VIEW
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The measurements in Tables 3 and 4 refer to series of large arboreal Oryzomys (Oecomys) concolor from eastern Colombia and to measurements of comparably large terrestrial series. Due to the distortions of the rear foot samples, it is not possible to give a reliable measurement of metatarsal width in relation to the length of the foot. On the other hand, the greater width of the metatarsus of the subgenus Oecomys (Fig. 4a,b) seems indeed to be a specialization for arboreal life.
Claws: Claws are thick, relatively short, curved, their tips sharp and raised well above the ends of the fingers. These claws cannot be used for bathing, and their position does not interfere with the function of the toes as grasping organs. In contrast, the claws of closely related terrestrial crickets, such as Oryzomys laticeps, are slender, slightly curved, and protect the fleshy tips of the toes when used m.
The tail of subgenus Oecomys appears to be slightly thicker than that of comparable sylvian cricetines of predominantly terrestrial habits.
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Thus, in orizomy the hind leg longer than 21.5 percent of the combined head and body length, or shorter than 21 percent, the more specialized it is. Likewise, the longer or shorter a tail is than the length of the head and body combined, the greater the specialization. This, in effect, implies that a specialized short-legged species cannot have evolved from a specialized long-legged form, or vice versa; and that a specialized long-tailed species cannot claim as its ancestor a specialized short-tailed species, or vice versa.
On the basis of the above criteria, Oryzomys (Oecomys) concolor is more arboreal specialized than 0. The two known species of the subgenus Oecomys breed in tree hollows, tangled masses of epiphytes or vines, palm fronds, abandoned bird nests and thatched roofs of houses. The smaller species is the one most often found in houses where arboreal habitats are simulated by palm-thatched roofs and natural timber frames.
Although one of the most common native house mice in tropical South America, it is not found in areas where.
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531 Table 3.-Oryzomys (Oecomys) concolor superans Thomas: External measure- Table3.-Oryzomys (Oecomys) concolor superans Thomas: External measurements (in millimeters) of a series of adults from Rio Caquetdregion, eastern Colombia.
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ARBOREAL RICE RATS — HERSHKOVITZ 533
The elevation range is from near sea level to about 1,500 meters above the western slope of the Cordillera Occidental.
ARBOREAL RICE RATS ^HERSHKOVITZ 535
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538 CONTINUATION OF THE NATIONAL MUSEUM vol. no. except an oki-like stripe on each side of the white breast in one. In five individuals of Canelos taken in March, the breast is slightly buff; between the same place, . taken in April 1910, and in two from the Rio Copataza and another from Montalvo, the breast being pure white.. mentioned were within a few miles of each other in the upper Efo Pastaza region. Specimens from Jollln, Jatun Yacu, Llunchi, Avila, Concepci6n, San Jose, and Rio Suno, all in the upper Rio Napo region, show the same range of variation in color as the preceding.
In a specimen from Llunchi, however, the belly is uniformly ochre-red and hardly defined from the sides. The series of 11 specimens from Rio Curaray, Loreto, Peru, includes individuals in dark and light pelage. The underside, upper lips, and lower half of the cheeks of one of two mice from Satipo, Junln, are yellowish.
The type series of Oecomys florenciae J.A. AUen, from eastern Colombia, is virtually indistinguishable from the typical hicolor as represented by any series from eastern Ecuador. Thomas is the "buffy ochreous" belly of the type compared to the pure white belly of the dryas {= western {s) type of western Ecuador. Of the two specimens present from the Rio Tapajoz, Pard, one, an adult from Limontuba, is as small cranially as the type; the other, from Igarap6 Bravo, is a subadult with a much larger skull.
Ni Allen, manipud Barao de Malga9o, Mato Grosso, Brazil, ket maitutop a nadayagnos iti orihinal a pannakailadawan kas “kapada ti sapasap a kolor ken kadakkel iti (E. Ecuador: Iti baba ti San Jos^, Rfo Payamino, Napo-Pastaza, 2 (AMNH); Rfo Suno, Rio Napo, Napo-Pastaza, 3 (AMNH);Avila, Rfo Suno, Napo-Pastaza,.
1 (CNHM)
540 COLLECTIONS OF THE NATIONAL MUSEUM vol.no Belem in Braganza, Pard, 1 (BM, paricola type); Recreio, Rio Majary, Amazonas, 1 (AMNH); Urucumde Corumbd, Mato Grosso, 1 (CNHM); Barao Malgago, Mato Grosso, 3 (including species milleri, AMNH); Urupd, Mato. Measurements of the paratype were not given, but Thomas stated that it was "about the same overall size" as the type. 542 PROCEEDINGS OF THE NATIONAL MUSEUM vol.no A skin without a skull from Ticunhuaya, Bolivia, not far from the type locality of the benevolens, seems to belong here.
544 PROCEEDmCS of IVUISEUM national voL.no Oryzomys laticeps* is a terrestrial species co-ranging with Oecomys. In co-staining, individual fusion from one color phase to another is evident in a large proportion of specimens. Type locality: Eio Curicuriari, an affluent of the upper Rio Negro, entering from the right below Sao Gabriel, Amazonas, Brazil.
The darker coloration of the upper parts in the type series indicates a wedge leading to the darker speciosa in northeastern Venezuela and Trinidad. Allen agrees with the color of the upper Rio Negro-Rio Orinoco region in terms of size, but they are more saturated on the lower parts and as dark on the upper parts and sides as 0. Morphologically and geographically, the mice of the Colombian foothills of the Andes in the Orinoco drainage are the closest to the true color.
Topotypes of illectusBangs from the equally wetter but cooler north slope of the Sierra are paler on average. They were taken from the beginning of the dry season in January to the beginning of the rainy season in April. Allen on one adult, both from localities near Bonda in the semi-arid northwestern corner of the Sierra Nevada de Santa Marta.
They are like the small pale mice of the ecologically similar valley at the western base of the Sierra. The range of variation in color, size, and degree of development of the supraorbital ridges shown by the mice of the Sierra Nevada de Santa Marta region is greater than in that of any other single region.
CNHM, 2)
Wagner compared the type concolor with the larger Hesperomys anguya (= Oryzomys buccinatus Olfers) and noted that in the former the color of the upperparts is much brighter and redder, the hair of the belly pure white, the cheeks without gray as in anguya, the feet covered with brownish hair, and the tail dark and with short hairs. My dogs found it in the opening of a hollow tree and I pulled it out using a pickaxe. The hairs are slightly longer at the roots of the claws, but do not reach the tips of the claws.
The size, color, broad hindquarters and relatively long and sparsely haired tail of concolor are characteristic of Oecomys.
ARBOREAL RICE RATS — HERSHKOVITZ 553 (AMNH); Villavicencio, Meta, 2 (AMNH, types of helvolus aud vicencianus)
554 PROCEEDINGS OF THE NATIONAL MUSEUM vol.no Distribution: Trinidad, Guiana, and eastern Venezuela, including the coast and delta and basin of the lower Rio Orinoco;. Characters: Like concolor, but darker throughout; upperparts brown finely marked with dark brown; underparts grey, sometimes white or pale with plumose basal parts of hairs showing. However, in diseased specimens, the basal parts of the abdominal and chest hairs are plumose and show through the surface.
Remarks: Of series of our specimens collected at Prince's Town, Trinidad, Allen and Chapman described one as Oryzomys speciosus. The basal parts of the abdominal hairs in the first are more nearly white than in the others. The authors noted that "in size, proportions, and color [speciosus] is strongly suggestive of Hesperomys concolor Wagner." Paradoxically, they failed to recognize the same relationship with the specimen they named.
The two specimens from Auyan-tepui on which the description of Oecomys auyantepui Tate is based are colored like other terrestrial representatives of the species speciosus. Distribution: Foothills, lower slopes, valleys, and foothills of the Andes drained by the Amazon in Colombia, Ecuador, and Peru, from about 200 to 1,200 meters above sea level. Characters: Largest and darkest of the subspecies; upperparts and sides brownish, the back evenly mixed or strongly edged with dark brown; underparts gray to yellowish orange or ornamental orange, dark leaden basal parts of hairs showing through; the throat and chest are not significantly different from the abdomen.
Most other specimens are in worn old pelts of one color phase with patches of new pelts of the next phase. One specimen collected in each of February, August and October is in old pelage. Others taken at the same time and during other months of the year are bad pelage.
Specimens from higher elevations in the valleys and slopes of the Andes (Zamora and Chonta Urcuin Ecuador; Moyobamba, Amazonas, and Hacienda Exito, Huanuco, in Peru) are smaller, have longer pelage, and are more richly colored, especially on the underside, than their relatives from the bottom of the The Cordillera. Oecomys palmeri Thomas is just a small topotype of superans collected on the same day by the same collector.
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Ti lokalidad ti tipo: Santa Ana de Chapada, Mato Grosso, Brasil; kangato, 800 metro iti ngatuen ti patar ti baybay. Panakaiwarwaras: Akin-amianan a Bolivia kadagiti departamento ti Beni, Cochabamba, Santa Cruz ken Chuquisaca iti laud aginggana idiay Mato Grosso, Brasil iti labneng ti Rio Paraguay; kangato ti agarup 200 agingga iti 1500 a metro. Dagiti espesimen manipud kadagiti departamento ti Bolivia ti Chuquisaca, Beni ken Santa Cruz ket mangipakita ti dakdakkel a panaglalaok ti natayengteng a kayumanggi iti akinngato a paset ken.
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ARBOREAL RICE RATS — ^HERSHKOVITZ 561
CNHM)
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Lateral aspect (X2) of the left mandible of the same skulls shown in plates 8-lU: a, Oryzo^nys biro/ose; b,0.concolor;c,0.
