Scolomys juruaense Patton and da Silva 1995

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 : 160-162

Scolomys juruaense Patton and da Silva 1995

TYPE LOCALITY: ‘‘Seringal Condor, left bank Rio Jurua´, Amazonas, Brazil 70°51̍W 6°45̍S.’’

DESCRIPTION: This genus consists of smallbodied, spiny mice with a tail shorter than head and body length, short and fleshy feet short and rounded ears, and dark reddishblack to brownish­black dorsal coloration and gray venter. It can be confused only with members of the genus Neacomys , which also have spiny dorsal fur. A complete set of comparisons between the two genera is given in Patton and da Silva (1995). The readily recognizable and salient differences between Scolomys and Neacomys include, respectively, the following characters: (1) gray, as opposed to generally pure white venters; (2 three, as opposed to four pairs of mammae (3) skull (fig. 106) short with blunt rostrum flanked by very shallow zygomatic notches as opposed to more narrow and elongate rostrum with deeper notches; (4) supraorbital margins rounded with moderately developed

overhanging ledges, rather than raised ridges; (5) interorbital region broad, greater than width of rostrum, as opposed to equal to or less than rostral width; (6) derived carotid circulation pattern comprised only of internal carotid artery, with greatly reduced to absent stapedial foramen, no squamoso­alisphenoid groove or sphenofrontal foramen, as opposed to either primitive carotid pattern or derived, but with well­developed stapedial foramen indicative of a stapedial artery; (7) sphenopalatine vacuities greatly reduced, as opposed to broadly open; (8) upper incisors proodont to orthodont, as opposed to opisthodont; and (9) molar teeth with weakly developed cusps that obliterate quickly with wear, as opposed to well­developed and long­lasting cusps.

Scolomys juruaense , the species we have recently described from the Rio Juruá basin, is readily distinguished from the type species of the genus, S. melanops , which is now known from extreme northern Perú and eastern Ecuador, by its combination of (1) longer and more slender rostrum, (2) orthodont rath­ er than proodont upper incisors, (3) somewhat larger cranial dimensions, (4) narrow and parallel zygomatic arches, (5) occluded subsquamosal fenestra ; and (6) gracile mandible with longer, more curved, and narrower coronoid process. This species is very similar in cranial shape to the third known member of the genus, S. ucayalensis Pacheco from northern Peru´ , but differs in larger cranial dimensions, reddish­brown as opposed to dark gray dorsal coloration, ‘‘stepped’’ rather than evenly tapered lateral margins of the incisive foramina, and square rather than distinctly rounded anterior margin of the mesopterygoid fossa .

SELECTED MEASUREMENTS: Means and ranges (from Patton and da Silva, 1995) are given in table 45.

DISTRIBUTION AND HABITAT: Known only from four localities in the central and upper reaches of the Rio Jurua´, Amazonas and Acre states, western Brazilian Amazon. Although we caught all of our specimens in undisturbed terra firme forest on the ground, these sites were often in areas of local, natural disturbances, such as tree falls.

REPRODUCTION: Pregnant females or those with a perforate vagina were obtained from August through March, suggesting that breeding occurs in both wet and dry seasons and perhaps throughout the year. Embryo counts ranged from one to three.

COMMENTS: While superficially similar in external morphology to spiny mice of the genus Neacomys , these two genera differ so trenchantly in other features that they cannot be considered close relatives (Patton and da Silva, 1995). This view is supported by the preliminary molecular sequence data provid­ ed by Patton and da Silva (1995) for seven genera of oryzomyine rodents, including Scolomys . In this analysis, Scolomys was quite divergent from all other genera in the tribe, and no particular relationship could be supported given the 801 base pairs of sequence then available. The genus is apparently unique among the Oryzomyini in having only three, as opposed four, or more, pairs of mammae (see Voss and Carleton, 1993, for a discussion of the morphological characters of oryzomyine rodents).

SPECIMENS EXAMINED (n = 23): (4) 1m, 4f — INPA 2485–2486, MPEG 24023–24024, MVZ 183172; (6) 3m, 2f — MPEG 23824 (holotype), 24019–24020, MVZ 183167– 183168; (7) 3m, 2f — INPA 2487–2488, MPEG 24022, MVZ 183165–183166; (12) 6m, 2f — INPA 2489–2492, MPEG 24021, MVZ 183169–183171.

TRIBE THOMASOMYINI VORONTSOV, 1959