Oecomys concolor (Wagner)

Carleton, Michael D., Emmons, Louise H. & Musser, Guy G., 2009, A New Species of the Rodent Genus Oecomys (Cricetidae: Sigmodontinae: Oryzomyini) from Eastern Bolivia, with Emended Definitions of O. concolor (Wagner) and O. mamorae (Thomas), American Museum Novitates 3661, pp. 1-32 : 21-24

Oecomys concolor (Wagner)

Hesperomys concolor Wagner, 1845: 147 (type locality: Brazil, Amazonas, Rio Curicuriari, a tributary of the upper Rio Negro, below São Gabriel [as amplified by Hershkovitz, 1960: 547]; holotype: NMW B482).

[ Oryzomys (Orzyomys)] concolor: Tate, 1932: 3 (name combination, taxonomic history).

Oryzomys (Oecomys) concolor concolor: Hershkovitz, 1960: 545 (genus-group revision, retention as valid species and nominotypical subspecies).

Oecomys concolor: Gardner and Patton, 1976: 13 (name combination, karyotype).

Rhipidomys marmosurus Thomas, 1899: 378 (type locality: Colombia, Vichada, middle Río Orinoco, Maipures ; holotype: BMNH 1899.9.11.38).

[ Oryzomys (Oecomys)] marmosurus: Thomas, 1906a: 445 (name combination, allocation to new subgenus).

O [ecomys] marmosurus: Thomas, 1910: 187 (name combination).

Oryzomys marmosurus: Ellerman, 1941: 358 (name combination).

Oryzomys (Oecomys) concolor concolor: Hershkovitz, 1960: 546 (subgeneric revision, marmosurus allocated as full synonym).

Oecomys concolor: Musser and Carleton, 1993: 716 (name combination, marmosurus listed as synonym without indication of rank).

EMENDED DIAGNOSIS: A species of Oecomys ( Sigmodontinae : Oryzomyini ) characterized by a combination of medium-large size (HFL <26–28 mm, ONL <31–33 mm), relatively long tail (TL <140–155 mm), very short pelage, relatively narrow incisive foramina, presence of alisphenoid struts, and a derived carotid circulatory pattern (skull lacking squamosal-alisphenoid groove, sphenofrontal foramen, and posterolateral groove on the parapterygoid plate; posterior opening to the alisphenoid canal compressed; stapedial foramen absent; groove dorsally crossing the parapterygoid plate present).

DISTRIBUTION: Lowland rainforest to the north of the rios Amazonas–Solimões in northwestern Brazil and to the south of the Río Orinoco in eastern Colombia and southern Venezuela (fig. 6). Known elevational range sea level to 400 m.

REMARKS: In 1848, Wagner amplified his initial brief diagnosis ( Wagner, 1845) of concolor under Hesperomys , a catchall genus of the middle 1800s whose definition and contents were nearly equivalent to the subfamily Sigmodontinae as its taxonomic boundaries are understood today (translation below by E. Brothers; see appendix 2 for original Latin and German text):

5. Hesperomys concolor Wagner. The monochromatic ‘‘scharrmaus.’’

H [esperomys concolor is] tawny, abruptly white below, with feet becoming darker; tail naked and as long as the body; with the hairs of the belly a uniform color.

Hesperomys concolor . A. Wagner in Archiv für Naturgeschichte 1845: 147.

We have viewed this species initially as a modification of Hesperomys Anguya ; after I had made a careful comparison with the latter, it appeared more proper to me to consider it a species. It is in all ways very closely related to H. Anguya, but the coloring of the dorsum is far livelier, mixed with more red and sprinkled with black. The underside, which is a beautiful white, has hair that is purely of one color, in contrast to the twocolored H. Anguya; furthermore, the gray coloring of the cheeks is absent and the feet are covered with brownish hairs; the naked tail, with only short fine hairs, has a dark coloring. The whiskers are black and the ears are haired in the same manner as H. Anguya. After Wagner’s description, concolor remained a forgotten name in the early nomenclatural history of oryzomyine rodents until Tate (1932) associated it with Oryzomys (Oryzomys) . Hershkovitz (1960) correctly recognized concolor Wagner as a species of Oecomys , ranked as subgenus, but had not examined any type material. Musser’s study of the type specimen of concolor (NMW B482; table 7 ) in 1992 supports Hershkovitz’s genusgroup association of the name, the oldest epithet assignable to Oecomys . The type is a young adult (sex indeterminate), with only moderate wear on the molars but in full adult pelage. Aspects of the holotype indicate that it was first preserved in alcohol and later stuffed and converted to a museum specimen. The tail is brittle but intact; the pinnae are somewhat tattered and paler than those observed in the recently collected Venezuelan series. The upperparts of the holotype are closely similar in fur length, texture, and color to material from the lowlands of Venezuela except that they are slightly redder, probably a result of initial preservation in alcohol. The chin and throat are gray, and the rest of the underparts are white except along the flanks, where the basal portions of the hairs are pale gray. As emphasized by his designation of the specific name, Wagner was impressed by the all-white underparts of the specimen before him, but coloration of the ventral pelage does vary within the series that we have examined. Many specimens possess small to broad expanses of gray over the middle abdomen, and some exhibit a strong overwash of buffy-tipped hairs; the dorsal-ventral pelage contrast is weakly defined in the latter condition. Impressions of the carotid branching preserved on the skull of the type specimen disclose a derived configuration—no sphenofrontal foramen or squamosal-alisphenoid groove, minute stapedial foramen, diagonal groove across dorsal surface of parapterygoid bone—the same traits that we have uniformly observed in all other specimens that we identify as O. concolor . Further, the type skull bears a strong alisphenoid strut on both sides, a condition observed in nearly all specimens of O. concolor examined ( table 5 ).

As mentioned by Wagner, the specimen on which he based his new species was obtained by Johann Natterer (1787–1843), an Austrian naturalist and early collector of birds and mammals in the Amazon Basin. Kurt Bauer of the Naturhistorisches Museum Wien kindly provided additional information about Natterer’s travels and the collecting site of the type (in litt. to GGM, 16 Jan 1984).

I found no information how far up the rio Curicuriari Natterer went, but all indications are, that he stopped just at the mouth or entered the lowest part. Oe. concolor seems to be the only mammal collected there, and the itinerary v. Pelzeln [August von Pelzeln, 1825–1891] provided in his work on Natterer’s birds [ Pelzeln, 1871] just mentions 5 August 1831 represented by a bird collected there. From his data … and our notes, it is clear that J. Natterer stayed at least until 15th July at the Rio Vaupe/Uaupes and collected at Barcellos/Barcelos about 500 km downriver on the Rio Negro from August 23rd onward.

Thus, the standard coordinates for the mouth of the Río Curicuriari (appendix 1), a southern tributary of the Río Negro, may reasonably approximate the geographic source of Natterer’s specimen and Wagner’s type of Hesperomys concolor .

The holotype of marmosurus (BMNH 1899.9.11.38; table 7 ) possesses a bright ochraceous-tawny dorsum, resembling the more intensely colored specimens in the recent Venezuelan series. The belly is white overwashed with buff. The skull clearly exhibits the key traits of a derived carotid circulatory pattern and possesses well-developed alisphenoid struts on both sides.

The construct of O. concolor promulgated by Hershkovitz (1960) consisted of five subspecies ( concolor , speciosus , superans , roberti, bahiensis) whose collective distribution matched that of the genus in lowland rainforest of Central and South America. The highly variable morphology and pantropical range of his form reflected its composite nature, which embraced, either entirely or in part, at least nine valid species among the synonyms ( auyantepui , catherinae , concolor , flavicans , mamorae , roberti , speciosus , superans , trinitatis , as per Musser and Carleton, 2005). To our knowledge, only one speciesgroup epithet, marmosurus Thomas (1899) , properly belongs as a subjective junior synonym of O. concolor ( Wagner, 1845) . Divorced of these other species, O. concolor sensu stricto is seen to exhibit a somewhat specialized morphology, with limited boundaries of variation, and this morphology has a very restricted distribution within the genus. The geographic occurrence of O. concolor is confined to the Rio Negro West subregion of northern Amazonia, an area of endemism delineated from phlyogeographic and distributional studies of neotropical birds ( Cracraft and Prum, 1988; Stotz et al., 1996).

SPECIMENS EXAMINED: 63, as follows. Brazil — Amazonas, Rio Curicuriari, a tributary of the upper Rio Negro, below São Gabriel ( NMW B482 , holotype of concolor ); Ilha das Onças , left bank Rio Negro , 01 ° 49 9 57 0 S /61 ° 22 9 49 0 W (INPA-JLP 16806, 16807, INPA-LC 168, 178, INPA-YL 161); Lago Meduini , left bank Rio Negro , 01 ° 47 9 07 0 S / 61 ° 23 9 39 0 W (INPA-JLP 16795, INPA-LC 176); Macaco , left bank Rio Jaú , 24 m, 02 ° 05 9 01 0 S / 62 ° 07 9 21 0 W (INPA-LC 124, 128, 137–139, INPA- YL 127, 129, 131, 133); Macaco, right bank Rio Jaú , 02 ° 04 9 30 0 S /62 ° 06 9 21 0 W (INPA-YL 144, 146, INPA-LC 151, 154); vicinity of Comunidade Tambor, left bank Rio Jaú , 02 ° 14 9 S / 62 ° 26 9 W (INPA-MNFS 2038, 2040, 2051, 2057, 2059, 2060); Rio Uaupes , 2 m opposite Tahuapunta, 00 ° 36 9 N / 69 ° 11 9 W ( AMNH 78630 ) ; Yavanari, right bank Rio Negro , 00 ° 32 9 S / 64 ° 49 9 W ( AMNH 79400 ) . Roraima, Rio Uraicoera (joins the Rio Tacutu to form the Rio Branco ), 03 ° 02 9 N / 60 ° 29 9 W ( BMNH 1933.12.4.5) . Colombia — Meta, 18 km S San Juan de Arama, Los Micos , 1300 ft ( FMNH 87966 , 87968 ) . Vichada, middle Río Orinoco, Maipures ( BMNH 1899.9 .11.38 [holotype of marmosurus ]) . Venezuela — Amazonas, Río Cunucunuma, 48 km NW Esmeralda and 13 km SSW Belén, Acanaña ( USNM 406021 , 406022 ) ; Río Cunucunuma, 56 km NNW Esmeralda, Belén , 150 m ( USNM 406013 ) ; 68 km SE Esmeralda, Boca Mavaca , 138 m ( USNM 406014–406020 ) , 185 m ( USNM 374322–374325 ); Río Manapiare , San Juan , 155 m ( USNM 409862 , 409863 , 418444 ); Río Orinoco, Tamatama , 135 m ( USNM 409880 , 416712 , 416713 ); Río Orinoco, Caño Derecho (stream meeting Río Orinoco on its right bank), 02 ° 48 9 N / 65 ° 14 9 W ( AMNH 78069–78072 , 78545 ); Río Casiquiare , 250 ft, 02 ° 48 9 N / 65 ° 55 9 W ( AMNH 77319 ); 12 mi W Río Jawasu, left bank of Río Casiquiare, 01 ° 58 9 N, 66 ° 42 9 W ( AMNH 77328 ); Río Casiquiare, El Merly, 03 ° 05 9 N / 65 ° 55 9 W ( AMNH 78073 , 78074 ). Apure, 60 km NE Puerto Páez, Cinaruco River, Hato Caribén , 76 m ( USNM 374321 ) .