Oryzomys macconnelli Thomas, 1910

VOSS, ROBERT S., LUNDE, DARRIN P. & SIMMONS, NANCY B., 2001, The Mammals Of Paracou, French Guiana: A Neotropical Lowland Rainforest Fauna Part 2. Nonvolant Species, Bulletin of the American Museum of Natural History 2001 (263), pp. 1-236 : 120-140

Oryzomys macconnelli Thomas

VOUCHER MATERIAL: MNHN 1998.674– 1998.676. Total = 3 specimens.

IDENTIFICATION: Our three Paracou vouchers (collected by O. Henry, see below), together with additional material that we examined from other French Guianan localities, agree with Musser et al.’s (1998: 225–232) description of Oryzomys macconnelli , an identification that we confirmed by direct comparison with Thomas’s (1910) type series from the Supenaam River, Guyana. Although the French Guianan material averages small­ er than the type series in many dimensions (table 33), most French Guianan specimens are young adults (with lightly worn molars) whereas the type series is composed of older specimens (with more advanced toothwear). In the absence of other noteworthy differences between the two series, most of the observed measurement divergence could be attributed to sample age composition. The longer molar rows of the Guyanese series, however, cannot be attributed to advanced age, and the observation of even longer toothrows in some Venezuelan series (LM averages 5.2 mm in 12 specimens that we measured from Estado Bolívar) suggests that a real east­to­west size gradient may exist among O. macconnelli populations from the Guiana subregion of Amazonia. Western Amazonian samples are even more divergent morphometrically (Musser et al., 1998: fig. 106), and available karyotypes from western Amazonia differ dramatically from those of the single population sampled for chromosomes in the Guianan subregion (op. cit.: fig. 105). In the event that western Amazonian populations currently referred to O. macconnelli merit formal taxonomic recognition, the name O. mureliae J. A. Allen , based on a specimen collected in eastern Colombia, is available (Musser et al., 1998: 278–280). The Paracou population, however, is unambiguously assignable to O. macconnelli , or to the nominate race if a trinomial nomenclature is adopted.

Based on the samples at hand from Paracou and other localities in French Guiana, adult specimens of Oryzomys macconnelli can be readily distinguished in the field from O. megacephalus and O. yunganus by their larger external dimensions (especially hindfoot length: tables 33, 34), brighter pelage colors (redder dorsally and whiter ventrally versus drab brown dorsally and grayer ventrally in megacephalus and yunganus ), longer dorsal fur (12–15 mm versus <10 mm in megacephalus and yunganus ), sharply bicolored tails that are slightly longer than headsand­bodies (versus indistinctly bicolored or unicolored­dark and shorter in megacephalus and yunganus ), and six plantar pads on the hindfoot (versus five in most yunganus , see below). Oryzomys macconnelli also has a longer rostrum than either of the other spe­

cies with which it is sympatric in French Guiana, a contrast that is obvious in cranial comparisons (Musser et al., 1998) but can also be seen in living specimens.

OTHER SPECIMENS EXAMINED: French Guiana —Arataye ( MNHN 1983.371 – 1983.373 , 1986.276 ), St.­Eugène ( MNHN 1994.126 , 1994.127 , 1995.208 , 1998.1842 – 1998.1844 ), Saül ( MNHN 1983.365 , 1983.367 ). Guyana —‘‘ River Supinaam’ ’ ( BMNH 10.5.4.29– 10.5.4.34 [type series]). Venezuela — Bolívar, San Ignacio Yuruaní ( AMNH 257236– 257238 ; MHNLS 7831 , 7836 , 7880 , 8075 , 8076 , 8088 ; USNM 448584–448586 ) .

FIELD OBSERVATIONS: Our only records of Oryzomys macconnelli at Paracou are based on three specimens trapped by O. Henry, none of which were accompanied by ecological information.

Oryzomys megacephalus Fischer Figure 53A

VOUCHER MATERIAL: AMNH 266494 , 266497 , 266498 , 266501 , 266502 , 266504 , 266508 , 266514 , 266515 , 266518 , 266521 , 266523 , 266525 , 266527–266530 , 266533 , 266535 , 266538 , 266539 , 266541 , 267018 , 267566 ; MNHN 1995.999 – 1995.1010 . Total = 36 specimens .

IDENTIFICATION: At Paracou, and apparently throughout most of Amazonia, Oryzomys megacephalus (formerly O. capito , see below) occurs sympatrically with another morphologically similar species, O. yunganus (see range maps in Musser et al., 1998). Both are drab­colored Oryzomys with brownish dorsal fur, whitish­gray ventral fur, and indistinctly bicolored or unicolored­dark tails that average a little shorter than heads­andbodies. Comparisons of external measurements from our voucher material suggest that French Guianan O. megacephalus have slightly longer tails than sympatric O. yunganus , but the difference in average values for the ratio LT/HBL is small (0.94 versus 0.89) and insufficient for field identification because of overlapping variation (the observed range in this ratio among our vouchers is 0.78–1.03 for megacephalus , 0.69– 1.13 for yunganus ). Our measurement data suggest no appreciable species difference in absolute or relative size of the hindfoot. On

TABLE 33 Measurements (mm) and Weights (g) of Oryzomys macconnelli from French Guiana and the Type Localitya

average, megacephalus has somewhat bright­ er adult dorsal pelage than yunganus , but the difference is subtle and not useful for field identification.

The only external character potentially useful for distinguishing Oryzomys megacephalus from O. yunganus in the field is the number of plantar pads on the hindfoot (for illustrations, see Musser et al., 1998: fig. 17). Almost all specimens of megacephalus have six plantar pads: thenar, hypothenar, and four interdigitals. By contrast, most French Guianan yunganus have five pads because the hypothenar is absent (table 35). One Paracou specimen of megacephalus (AMNH 266527), however, lacks the hypothenar completely on one foot and has only an indistinct hypothenar on the other. Similarly, a few yunganus from Paracou (e.g., AMNH 266495, MNHN 1995.994) have distinct hypothenars on one or both hindfeet. Based on our tabulation of trait frequencies, a conser­ vative approach to identifying these species in the field in French Guiana (classifying animals with six distinct plantar pads on both hindfeet as megacephalus and those with only five pads on both feet as yunganus ) would leave an estimated 3% of specimens undetermined (i.e., those with asymmetrical numbers of pads, plus those with indistinct hypothenars on both feet) and would result in an expected error rate of about 5% (mostly yunganus misidentified as megacephalus ).

The only truly reliable basis for identifying megacephalus and yunganus is cleaned cranial material, from which diagnostic molar characters can be determined. All of the Paracou vouchers we identify as megacephalus have (1) the long paraflexus and single fossette on M2, and (2) the long hypoflexid, diagonal median murid, and lack of fossetid on m2 described and illustrated by Musser et al. (1998). By contrast, specimens we identify as yunganus have (1) a short paraflexus and two fossettes on M2, and (2) a short hypoflexid separated from a lingual fossetid by a less oblique median murid on m2 (op. cit.). Our multivariate statistical analyses of cranial measurement data from Paracou vouchers identified by these molar traits reveal that specimens of megacephalus have, on average, wider incisive foramina and narrower zygomatic plates than likesized examples of yunganus . However, measurement variation is too extensive for cranial proportions to be used as the sole basis for species identification at this locality. Although molar measurements differ significantly between sympatric samples of megacephalus and yunganus from some parts of Amazonia (Musser et al., 1998: table 8), these species do not diverge in dental dimensions at Paracou.

Husson (1978) and most other recent authors have called this species Oryzomys capito (Olfers) , but Tate (1939) referred Guianan populations to O. laticeps (Lund) . Both capito Olfers and megacephalus Fischer are based on Azara’s (1801) description of the ‘‘Rat Seconde ou Rat à Grosse Tête’’ from Paraguay. Musser et al. (1998) designated a Paraguayan neotype for megacephalus and explained why this name should replace capito (a junior objective synonym). Musser and his colleagues also diagnosed Oryzomys la­

TABLE 34 Measurements (mm) and Weights (g) of Oryzomys megacephalus and O. yunganus from Paracoua

ticeps as a distinct species restricted to the Atlantic rainforest region of southeastern Brazil.

As understood by Musser et al. (1998), Oryzomys megacephalus occurs throughout

TABLE 35 Frequency of Occurrence of the Hypothenar Pad on the Hindfeet of Oryzomys megacephalus and O. yunganus from French Guianaa

Amazonia and extends southward into the Paraná basin of eastern Paraguay. Morphometric, karyotypic, and molecular data summarized by Musser and his colleagues, however, strongly suggest that western Amazonian populations (characterized by large size, diploid counts of 52 chromosomes, and distinctive mtDNA haplotypes) are genetically and evolutionarily distinct from Paraguayan and eastern Amazonian populations (characterized by small body size, diploid counts of 54 chromosomes, and different mtDNA sequences). Although Musser et al. (1998) recognized this dichotomy, they emphasized the difficulty of identifying geographically intermediate samples as belonging to either the eastern or western clades by morphological criteria and provisionally regarded all of their megacephalus ­like Amazonian material as conspecific. Patton et al. (2000) subsequently recognized the western Amazonian form as a distinct species, O. perenensis J. A. Allen , a decision with which we concur.

In fact, Oryzomys megacephalus may be composite even in the restricted sense of Patton et al. (2000) because their cytochrome­b sequence analyses (op. cit.: fig. 97) suggest that samples of the small 2N = 54 taxon from north and south of the Amazon form reciprocally monophyletic groups. In the event that these geographic moieties should prove to be diagnosably different by additional criteria, the oldest available name for the northern form (to which our Paracou sample is presumably referable) is velutinus J. A. Allen and Chapman (1893), based on a holotype collected at Princestown, Trinidad.

OTHER SPECIMENS EXAMINED: French Guiana —Arataye (MNHN 1986.287–1986.293, 1986.295, 1986.296, 1986.298–1986.301, 1986.314, 1986.878–1986.880, 1986.882), Cacao (MNHN 1980.275, 1983.370, 1986.278, 1986.279, 1986.316, 1986.493– 1986.499, 1986.501, 1986.506, 1986.511, 1986.514, 1986.531, 1986.533), Camopi (MNHN 1982.600, 1982.620), Cayenne (MNHN 1970.225, 1986.317, 1986.319, 1986.952, 1986.953), ‘‘Marais de Kaw’’ (MNHN 1986.1106, 1986.1107), Rorota (MNHN 1986.954, 1986.955), Piste St.­Élie km 16 (MNHN 1986.884–1986.886), Saül (MNHN 1981.181, 1983.368, 1983.369, 1986.489, 1986.492, 1986.518, 1986.521, 1986.525), Sauts de l’Itany (MNHN 1962.1024–1962.1028), Trois Sauts (MNHN 1981.150, 1982.616–1982.619, 1982.623– 1982.627, 1986.283, 1990.908–1990.910).

FIELD OBSERVATIONS: All of our definite records of Oryzomys megacephalus at Paracou are based on collected specimens. Of our 36 vouchers, 23 (64%) were taken in Sherman or Victor traps set on the ground, 7 (19%) were taken in Sherman or Victor traps tied to lianas 0.3–1.2 m above the ground, 5 (14%) were shot on the ground, and 1 (3%) was taken in a pitfall. Microhabitat notes accompanying 26 specimens shot or trapped on the ground record 18 captures under or beside logs, 4 captures under the roots or buttresses of fallen trees, 2 captures under tangled branches of fallen trees, 1 capture at the base of a buttressed tree, and 1 capture at the entrance to a hollow log. All of the shot specimens were encountered at night, and all of the other specimens were found in traps at or near dawn. Twenty­two specimens (61%) were taken in well­drained primary forest, 3 (8%) in swampy primary forest, 2 (6%) in creekside primary forest, 5 (14%) in

TABLE 36 Comparison of Capture­Habitat Frequencies between Oryzomys megacephalus and O. yunganus Trapped in Primary Forest at Paracoua

primary forest of unspecified character, and 4 (11%) in secondary vegetation. See table 36 and the following account for capturehabitat comparisons with O. yunganus .

Oryzomys yunganus Thomas

VOUCHER MATERIAL: AMNH 266495 , 266496 , 266503 , 266510 , 266511 , 266513 , 266516 , 266517 , 266520 , 266532 , 267017 , 267567 ; MNHN 1995.993 – 1995.998 . Total = 18 specimens .

IDENTIFICATION: See the account above for morphological comparisons with Oryzomys megacephalus , the only species with which O. yunganus could plausibly be confused.

Long unrecognized as a member of the Guianan fauna, O. yunganus was recently revised by Musser et al. (1998), who documented the extensive Amazonian distribution of this species by mapping all known collection localities (op. cit.: fig. 14). As noted by Musser and his colleagues, the geographic samples they refered to O. yunganus exhibit considerable divergence in body size. Especially notable are specimens from Guyana, Surinam, French Guiana, and eastern Amazonian Brazil, which are diminutive by comparison with specimens from Venezuela, Colombia, Ecuador, Peru, and western Brazil. For example, the observed range of variation in crown length of the upper molar series (LM) among our vouchers (4.3–4.6 mm; table 34) does not overlap with the observed range of variation among 52 specimens (including the type) that we measured from Colombia, Ecuador, Peru, and Bolivia (4.8–5.6 mm). Additionally, French Guianan samples of O. yunganus differ conspicuously from western Amazonian samples in the frequency of occurrence of the hypothenar pad on the hindfoot (Musser et al., 1998: table 7). The currently accepted provisional hypothesis, that these and other differences among samples currently referred to O. yunganus represent intraspecific geographic variation, merits testing by additional collecting at intermediate localities (op. cit.: p. 109), and by analyzing molecular sequence data from Guianan and western Amazonian populations (as by Patton et al., 2000).

OTHER SPECIMENS EXAMINED: Bolivia — Cochabamba, Charuplaya ( BMNH 2.1 .1.39 [holotype]) . Colombia — Caqueta´, Tres Troncos ( FMNH 72036 , 72051 , 72066 ) ; Meta, La Macarena ( FMNH 58778 , 58779 , 87969 , 87970 ) ; Putumayo, Río Mecaya ( FMNH 72067 ) . Ecuador — Pastaza, Río Capahuari ( FMNH 43268 , 43271 ), Río Yana Rumi ( FMNH 43265 ) . French Guiana — Arataye ( MNHN 1986.294 , 1986.297 , 1986.313 , 1986.881 , 1986.883 ), Cacao ( MNHN 1986.490 ), Cayenne and Rorota ( MNHN 1986.322 , 1986.324 , 1986.326 , 1986.327 , 1986.800 – 1986.803 ), Kaw ( MNHN 1986.1105 ) . Peru — Cuzco, Hacienda Cadena ( FMNH 65704 , 66399 , 66401 , 68630 , 68631 ), Quincemil ( FMNH 75242 , 75253 , 75254 , 75257 , 75259 , 75261–75264 , 75272 ; Huánuco, Chinchao ( FMNH 23721 , 23722 ), Hacienda Buena Vista ( FMNH 24544 , 24547 , 24548 ) ; Loreto, Río Pastaza ( BMNH 54.421 , 54.422 , 54.425 , 54.429 , 54.430 ) ; San Martín, Moyobamba ( FMNH 19376 , 19387 , 19392 ), Puca Tambo ( BMNH 26.5.3.31– 26.5.3.38, 26.5.3.40 –26.5.3.42; FMNH 19787 ) ; Surinam — Nickerie, Kayserberg Airstrip ( FMNH 93284 , 93286 ) .

FIELD OBSERVATIONS: All of our definite records of Oryzomys yunganus at Paracou are based on collected specimens. Our 18 vouchers represent only 16 sampling events, however, because pairs of juvenile individuals were taken in the same trap on two occasions. Of these 16 independent captures, 15 (94%) were in Sherman traps set on the ground, and one was in a pitfall. All of our specimens were found in the traps at or near dawn. Seven captures (44%) were in welldrained primary forest, another 7 were in swampy primary forest, 1 (6%) was in creekside primary forest, and 1 was in primary forest of unspecified character. Microhabitat notes accompanying 15 specimens record 4 captures under or beside logs, 3 captures at the bases of trees, 3 captures in dense undergrowth unsheltered by woody objects, 2 captures under tangled dead branches, 2 captures under fallen palm fronds, and 1 capture among the stilt roots of a standing tree.

Our capture data from Paracou are broadly consistent with specimen counts from other Amazonian localities (summarized by Musser et al., 1998) in suggesting that Oryzomys yunganus is less abundant than O. megacephalus wherever these species occur sympatrically. Although we sometimes caught both species in the same trapline on the same date, statistical comparisons of capture frequencies by habitat (table 36) suggest that O. yunganus prefers moister primary forest habitats (swamp or creekside formations) than does O. megacephalus . The latter species was also trapped above ground level on lianas, and in secondary vegetation, situations in which O. yunganus was not encountered. Future ecological studies of Amazonian rodent communities should test the hypothesis that O. yunganus is a habitat specialist by comparison with O. megacephalus , but we caution that destructive sampling (or molecular typing, as by Lavergne et al., 1997; Steiner et al., 2000) will be necessary in or­ der to obtain reliable taxonomic identifications for this purpose.

Rhipidomys nitela Thomas Figure 53C , 61B , 62A

VOUCHER MATERIAL: AMNH 267021 , 267580 , 267582 , 267583 , 267594 ; MNHN 1995.1011 , 1995.1012 . Total = 7 specimens .

IDENTIFICATION: The ten nominal taxa of Rhipidomys based on type material collected in the Guiana subregion of Amazonia appear to represent four valid species that can be readily distinguished by external and craniodental characters. Rhipidomys macconnelli de Winton (1900) (including subnubis Tate, 1939) and R. wetzeli Gardner (1989) have

TABLE 37 Diagnostic Characters and Geographic Ranges of Rhipidomys mastacalis , R. nitela , and R. venezuelae a

long, soft fur and a primitive carotid arterial circulation (pattern 1 of Voss, 1988); they occur in montane and premontane vegetation associated with rocky outcrops of the Pantepui complex (Tate, 1939; Handley, 1976; Gardner, 1989) and neither is known from French Guiana (where such habitats are absent). The other two species have shorter, coarser fur, a derived carotid arterial morphology (pattern 3 of Voss, 1988), and occur in lowland rainforest. One of the lowland rainforest species (represented by the Guian­ an holotypes of sclateri Thomas [1887] , bovallii Thomas [1911b], and aratayae Guillotin and Petter [1984]) is large (HF = 32–36 mm; LM = 5.9–6.8 mm) with gray­based ventral fur, whereas the other (represented by the Guianan holotypes of nitela Thomas [1901] , fervidus Thomas [1904], milleri Allen [1913b], and yuruanus Allen [1913b]) is small (HF = 24–28 mm, LM = 4.1–4.8 mm) with (usually) pure white ventral fur.

Although the oldest Guianan name for the large lowland species is Rhipidomys sclateri, Musser and Carleton ( 1993) and Tribe (1996) treated sclateri as a subjective junior synonym of leucodactylus Tschudi (1844) , the type locality of which is in eastern Peru. Only a single specimen, the type of R. leucodactylus aratayae , is currently known from French Guiana.

The oldest Guianan name for the small lowland species is Rhipidomys nitela , but nitela has often been treated (e.g., by Cabrera [1961] and Husson [1978]) as a junior synonym of R. mastacalis (Lund, 1840) , and some nominal taxa referable to nitela were originally described as subspecies of R. venezuelae Thomas (1896) . Based on our examination of types and other material, we agree with Musser and Carleton ( 1993) and with Tribe (1996) that nitela , mastacalis , and venezuelae represent three valid species with diagnostic morphological and karyotypic attributes, and with discrete geographic ranges (table 37). Our six Paracou vouchers together with 13 additional specimens subsequently collected at Les Nouragues (by F. Catzeflis and his colleagues from Montpellier) are ap­ parently the only examples known from French Guiana.

For the most part, external and craniodental measurements of French Guianan specimens of Rhipidomys nitela agree closely with those of the Guyanese type series (table 38). Although relative tail length appears to be divergent in the two samples (averaging about 130% of head­and­body length in French Guianan material versus 115% in the type series), methodological artifacts might explain this proportional difference between small series of specimens measured in the field by different collectors. By contrast, measurements of the hindfoot and of the molars (both measured by us) suggest that the populations in question do not differ much, if at all, in size. Because the French Guianan material additionally resembles the type series in qualitative characters, we interpret these samples as representing populations of a single species.

Some of Husson’s (1978: table 71) measurements of the hindfeet of Surinamese specimens that he identified as Rhipidomys mastacalis nitela are smaller than any that we or Tribe (1996) observed for this species. If Husson’s material was correctly identified, which we do not doubt, it is likely that the feet were simply mismeasured. The single weight datum that Husson tabulated for this species (150 g) was obtained from a female with three near­term embryos and is obviously not comparable with our weights of nonpregnant animals.

All of the specimens that we refer to Rhipidomys nitela (see below) appear to represent a morphologically cohesive taxon that is geographically limited to the Guianan and Southeastern subregions of Amazonia. Tribe (1996), however, recognized two isolated records of R. nitela from outside Amazonia. One of these records, consisting of the type series of R. nitela tobagi Goodwin (1961) from Little Tobago Island, is equivocal in our judgment because the diagnostic presence of a conspicuous caudal tuft (fig. 61B) cannot be confirmed from the two partially decayed fluid specimens of this taxon; possibly, these represent an insular form of the adjacent mainland species R. venezuelae . The other nonAmazonian record of R. nitela mapped by Tribe (1996: fig. 7.6) is improbably iso­

TABLE 38 Measurements (mm) and Weights (g) of Adult Rhipidomys nitela from French Guiana and the Type Localitya

lated on the northern Caribbean coast of Colombia. We examined the voucher in question ( MHNG 1706.75 , from Bonda, Departamento Magdalena), which differs from R. nitela by its pale bicolored tail and short (6 mm) caudal tuft ; in our opinion, this specimen represents another taxon, perhaps allied to R. venezuelae despite its short (4.6 mm) toothrow.

Recently, Anderson ( 1997) reported Rhipidomys nitela from eastern Bolivia, a considerable range extension that we attempted to confirm by examining his material. Of the two specimens that Anderson cited by number (AMNH 119406, UMMZ 156298), however, we were only able to locate one. That specimen, UMMZ 156298, is an example of Thomasomys resembling T. oreas Anthony (1926) . Therefore, as far as we have been able to determine by direct examination of museum specimens, R. nitela appears to be an Amazonian endemic that does not occur west of the north­south zoogeographic axis represented by the Rio Negro and the Rio Madeira.

Species of Oecomys externally resemble Rhipidomys by their large eyes, long vibrissae (extending well behind the pinnae when laid back alongside the head), short­broad hindfeet with semi­opposable fifth digits, and long tufted tails. At Paracou, O. auyantepui and R. nitela are of similar size and might be confused in the field. However, R. nitela and O. auyantepui differ in many external characters that are potentially useful for identification of specimens in hand. (1) Whereas the pinnae of R. nitela are blackish (contrasting in color with the fur of the head) and appear quite naked (a very sparse auricular pelage is visible only under magnification), the pinnae of O. auyantepui are not contrastingly colored and have a visible pelage of reddishbrown hairs. (2) The dorsal body pelage of R. nitela is very short (5–6 mm), somewhat coarse to the touch, and dull grayish­brown, but the dorsal fur of adult specimens of O. auyantepui is much longer (Ź 10 mm), very soft to the touch, and lustrous reddish­brown in appearance. (3) The ventral pelage of R. nitela is almost entirely self­colored (pure white or cream to the roots of the hairs), except immediately along the flanks (where some hairs have gray bases and white tips); by contrast, the ventral fur of O. auyantepui is mostly gray­based, except on the throat and along the midline (where some hairs are pure white). (4) The hindfeet of R. nitela are always prominently marked by a dark band of brownish hairs that extends from the ankle over all or part of the metatarsus to the base of the toes, which are usually white (pigmented hairs extend onto the proximal phalanges of the middle toes in a few specimens, but the outermost digits are always completely white); by contrast, pedal markings are not conspicuous in most specimens of O. auyantepui , some of which have uniformly pale feet. (5) Adult female specimens of Rhipidomys have six mammae in postaxial, abdominal, and inguinal pairs (muroid mammary loci are illustrated in Voss and Carleton, 1993: fig. 8), but female Oecomys have eight mammae (the additional teat­pair is pectoral).

Extended craniodental comparisons between Rhipidomys and Oecomys are unnecessary for fieldworkers, but it is relevant to note that these genera superficially resemble one another by their shallow zygomatic notches, convergent and beaded supraorbital margins, and pentalophodont molars. Nevertheless, skulls found in stomachs or scat can be easily identified by palatal architecture. The bony palate of Rhipidomys (fig. 62A) is ‘‘short’’ because it does not extend behind the molar rows, and the posterior palatal margin is biconcave because a small median palatal process is present; the posterior palatal pits are small, simple perforations. By contrast, the bony palate of Oecomys (fig. 62B) is ‘‘long’’ (extending behind the molar rows) with a typically arch­shaped posterior margin, and the posterior palatal pits are larger and often more complex. The only French Guianan species of Rhipidomys and Oecomys that are at all likely to be confused, R. nitela and O. auyantepui , can also be distinguished by carotid arterial morphology (pattern 3 versus pattern 1 [of Voss, 1988], respectively), but carotid morphology does not consistently differ between other representatives of these genera.

OTHER SPECIMENS EXAMINED: Brazil — Para´, Aramanay on Rio Tapajos ( AMNH 94810–94813 ). French Guiana —Les Nouragues ( AMNH 269821 ; V­824, —825, —826, —831, —876, —886, —890, —891, —893, —905, —914) . Guyana — Potaro ­Siparuni, Minnehaha Creek ( AMNH 36331– 36336 [type series of milleri]) ; Upper Takutu ­Upper Essequibo , Quatatat ( BMNH 1.6.4.81–1.6.4.86 [type series of nitela ]) . Venezuela — Bolívar, La Unión ( BMNH 4.5 .7.34, 4.5.7.35 [type series of fervidus]), La Vuelta ( BMNH 4.5.7.36), Río Yuruán ( AMNH 30727–30735 , 30737 [type series of yuruanus]), San Ignacio Yuruaní ( AMNH

because the mesopterygoid fossa does not extend anteriorly to the last molars; also, the posterolateral palatal pits of oryzomyines are large, sometimes complex, and frequently recessed in shallow fossae.

257273–257275; MHNLS 7845, 7846, 7848–7850, 7891, 7892, 7895, 7896, 7898, 7899, 8072, 8074; USNM 448613–448616, 448618–448623, 448625–448628).

FIELD OBSERVATIONS: All of our definite records of Rhipidomys nitela at Paracou are based on collected specimens. In 1992, one adult female was shot in the daytime as it perched several meters above ground level in the dark interior of a hollow tree (fig. 63). In 1993, the same tree cavity contained four individuals, of which one adult female and two juveniles were shot and one juvenile escaped. One specimen was captured at ground level in a pitfall, and two others were taken in platform traps 14.5–15.2 m above the ground. All of our vouchers were shot or trapped in well­drained primary forest.

ERETHIZONTIDAE

Coendou melanurus (Wagner) Figures 64 , 65 , 67 , 68 , 69 , 70A , 71

Only two specimens documented the occurrence of this distinctive porcupine in French Guiana prior to fieldwork at Paracou : the mounted skin of an immature animal from ‘‘ Guyane’ ’ ( MNHN 1909.241 ), and an adult skin­and­skull from St. Laurent du Maroni ( MNHN 1909.242 ). Just a single individual ( AMNH 266565 ) was encountered in our inventory, but simultaneous faunal rescue operations at the Petit Saut hydroelectric dam site resulted in 59 captures (Lemercier, 1998; Vie´, 1999), from which three specimens were salvaged as vouchers ( MNHN 1997.640 , 1997.641 , 1999.1080 ; F. Catzeflis, personal commun.). Evidently, the species is not rare, but cryptic. Because the morphological and geographic limits of Coendou melanurus are not adequately documented in the literature, we redescribe the species below, discuss its morphological variation, compare it with other congeners, and provide new information about its geographic range .

TYPE MATERIAL: Wagner’s (1842) original material of Cercolabes melanurus consists of two specimens in the Naturhistorisches Museum Wien collected by Johann Natterer at Barra do Rio Negro (= Manaus), Estado Amazonas, Brazil. 19 Both are skins, originally stuffed and mounted for exhibition, with skulls and mandibles subsequently extracted.

In order to clarify the application of Cercolabes melanurus , we select as lectotype NMW 42010, an adult female collected in February 1834. The skull (fig. 64) is that of a fully mature animal, with slightly swollen frontal sinuses and most cranial sutures fused ; the cheekteeth are worn flat, but all essential details of the occlusal morphology remain. The squamosal root of the right zygomatic arch is broken, as is the right pterygoid process; both occipital condyles and part of the basioccipital are missing. The skin (fig. 65) is essentially intact, but the tail is partially broken away at the base and secured to the body with thread. The paralectotype ( NMW B­1017) is a subadult female with deciduous premolars and unfused cranial sutures. Like the lectotype, the tail of this specimen is partially broken away and tied to the body with thread .

DISTRIBUTION: Specimens that we examined and literature records that we judge to be reliable suggest that Coendou melanurus ranges throughout the Guiana subregion of Amazonia (fig. 66). Although Emmons ( 1990, 1997), Alberico et al. (1999), and Tirira (1999) described the range of C. melanurus as extending into western Amazonia, all extralimital records that we investigated were found to be based on misidentified material of other species (see Comparisons, below).

DESCRIPTION: Small long­tailed porcupines (see measurements in table 39) with dorsal pelage composed of short quills more­or­less concealed beneath a thick coat of long blackish fur coarsely streaked with yellow. Quills bicolored (yellowish basally with darkbrown tips), about 3 cm or less in length, densely covering dorsal surface of head, neck, trunk, and upper limbs, but only exposed on cheeks and crown of head (except where fur has come away in patches due to

19 A third specimen in the same museum (NMW B­ 1006), consisting of a stuffed skin with skull and mandibles inside, lacks locality information and is not part of Natterer’s collection from Barra do Rio Negro (Pelzeln, 1883). According to the museum’s acquisition catalogs and card files, NMW B­1006 was purchased in London by L. v. Fichtel in 1809 and may have originated from the Guianas (K. Bauer, personal commun.).

(Wagner). Both views approximately Χ0.5.

faulty preservation). Dorsal fur long and abundant, concealing quills from crown to rump; individual hairs pale basally (among the quills), but emergent fur black heavily streaked with pale yellow (a mass effect pro­ duced by coarse guard hairs with very long yellow tips scattered abundantly among finer hairs that are entirely black or have only inconspicuous pale tips). Ventral surface of body without offensive quills, covered sparsely with short, coarse, brownish hairs (usually frosted with whitish bands or tips) from chin to anus. Face with very short quills on forehead and cheeks but otherwise almost naked, especially around eyes; facial vibrissae consisting of long, black mystacial, genal, and superciliary hairs; submental vibrissae short and black. Pinnae rudimentary and almost naked. Hands and feet covered dorsally with very coarse blackish hairs. Tail probably about as long as head­and­body on average; dorsum of proximal third with body pelage (quills and yellow­streaked black fur), but remainder of tail (except for naked prehensile surface) densely covered above and below with stiff black bristles.

Frontal and nasal sinuses uninflated (resulting in a flattened dorsal profile from midparietal region to nasal tips) or weakly inflated (resulting in a noticeable bulge over the orbits). Rostrum usually short and very broad, not conspicuously excavated laterally for origin of infraorbital muscle; nasals parallel­sided or weakly convergent posteriorly, with rounded posterior margins that extend well behind the premaxillae. Zygomatic

TABLE 39 Measurements (mm) of Coendou melanurus

arches (viewed from above) usually with rounded lateral deflection at orbits, but sometimes convergent anteriorly with no orbital deflection (e.g., AMNH 266565); jugals moderately expanded dorsoventrally behind maxillary suture. Dorsolateral contours of braincase weakly sculpted by bony scars of M. temporalis in most specimens (but temporalis scars well marked in AMNH 70120), the right and left scars always widely separated (never joined to form a sagittal ridge or crest).

Incisive foramina short and completely contained by premaxillae (e.g., AMNH 94174), or longer and bordered by maxillae posteriorly; left and right foramina recessed in a common fossa and incompletely separated (e.g., AMNH 94174) or completely separated by a stout bony septum and not recessed (e.g., AMNH 142955). Posterior diastema usually distinctly trisulcate; palatal bridge usually without a distinct median keel, or keel weakly developed (never a high crest flanked by deep lateral gutters). Anterior margin of mesopterygoid fossa a broad, blunt wedge penetrating between third molar crowns; bony roof of mesopterygoid fossa usually completely ossified (sometimes with tiny perforations but never large vacuities). Auditory bullae very large and antero­posteriorly elongated; roof of external auditory meatus with conspicuous bony ridge extending from dorsal lip of bulla to malleus.

VARIATION: This species is extraordinarily uniform in qualitative external characters despite the apparent plasticity of some morphometric and osteological traits. High variability in external measurements (table 39) is common in erethizontids because of the difficulty of handling animals protected by sharp quills; additionally, porcupine feet do not resemble those of other rodents, and some field collectors may have measured the hindfoot erroneously, from the rounded posterior margin of the plantar callosity instead of the heel. As in other caviomorphs, qualitative cranial and dental characters of erethizontids are annoyingly variable. Some differences among the specimens of Coendou melanurus that we examined may be corre­ lated with age and sex, but with miniscule samples from widely scattered localities, interpretation is difficult.

COMPARISONS: Many faunal accounts and checklists (e.g., Cabrera, 1961; Husson, 1978; Woods, 1993) have treated Coendou melanurus as a subjective junior synonym of C. insidiosus (Olfers, 1818) , a taxon endemic to the Atlantic rainforests of southeastern Brazil. The history of this erroneous usage was reviewed by Voss and Angermann ( 1997), who rediscovered and redescribed the holotype of C. insidiosus , compiled geographic data from other known specimens, and provided diagnostic comparisons with C. melanurus . Morphological differences between these highly distinctive species are here illustrated for the first time (figs. 67– 70).

Other species of South American porcupines with long fur are easily distinguished from Coendou melanurus by conspicuous external characters. For example, Coendou vestitus Thomas (1899c) and C. pruinosus Thomas (1905) from Venezuela and Colombia are smaller, shorter­tailed porcupines that have long wire­like bristles mixed among the quills and woolly fur of the dorsal pelage. We have also examined several Ecuadorean specimens previously misidentified as C. melanurus and determined that they represent an undescribed species of the vestitus group; this taxon superficially resembles melanurus because it has long yellow­tipped bristles that contrast with the black­tipped quills to produce a similarly streaked pelage pattern. However, the new species is substantially smaller (HF, 58–59 mm; CIL, 58.8–64.4 mm; MTR, 14.1–15.2 mm), lacks a dense coat of long adult fur, and has more acutely angled mesopterygoid margins that penetrate more deeply between the toothrows (Voss and da Silva, submitted).

Throughout the Guiana subregion of Amazonia, Coendou melanurus is sympatric with another congener, C. prehensilis (see below). Although melanurus is smaller than prehensilis , there is some overlapping variation in weights and linear dimensions from large sympatric samples (Richard­Hansen et al., 1999). Fortunately, the two species are unmistakeable in qualitative external characters (fig. 71). Diagnostic craniodental compari­ sons between Surinamese samples of melanurus and prehensilis were discussed by Husson (1978), who misidentified his material of the former species as Sphiggurus insidiosus (see above and Remarks, below)

REMARKS: Coendou melanurus and other long­furred Neotropical porcupines have often been referred to the genus Sphiggurus F. Cuvier (most recently by Husson, 1978; Concepción and Molinari, 1991; Woods, 1993; Eisenberg and Redford, 1999). However, we agree with Handley and Pine (1992) that Coendou and Sphiggurus are not meaningfully diagnosable based on current knowledge of morphological character variation, and that the latter name should be treated as a subjective junior synonym of the former.

Sphiggurus melanurus Gray (1842) , published in the same year as Cercolabes melanurus Wagner , is based on a skin in the Natural History Museum (London) bearing the number 86a on a cardboard tag attached to the hindfoot. This specimen agrees in every essential respect with Wagner’s type series and with the other material herein referred to Coendou melanurus . Waterhouse (1848: 425), the first reviser in the sense of the International Code of Zoological Nomenclature (ICZN, 1999), can be considered to have chosen Wagner’s name to have precedence over Gray’s (a junior subjective synonym).

SPECIMENS EXAMINED: Brazil —‘‘ Brazil’ ’ ( BMNH specimen numbered 86a in J. E. Gray’s manuscript catalog [type of melanurus Gray ]) ; Amapa´ , Serra do Navio ( USNM 394732 ) ; Amazonas , Manaus ( NMW 42010, B­1017) ; Para´ , Lago Claimy on Rio Jhamunda ( AMNH 94174 ). French Guiana — ‘‘Guyane’’ ( MNHN 1909.241 ), Paracou ( AMNH 266565 ), St.­ Laurent du Maroni ( MNHN 1909.242 ). Guyana — Cuyuni ­Mazaruni, Kartabo ( AMNH 70120 , 70131 , 142955 ) ; Demerara ­Mahaica , Georgetown ( FMNH 17762 ) ; Upper Takutu ­Upper Essequibo , 25 mi E Dadanawa ( ROM 31984), Nappi Creek near Letham ( ROM 31683, 31783 , 31801 ). No locality data —( NMW B­ 1006) .

FIELD OBSERVATIONS: Our single voucher is the only definite record we have of Coendou melanurus from Paracou; surprisingly, none of the forestry personnel whom we in­

(bottom, AMNH 90119). All views approximately life­size.

terviewed were aware that this species occurred in the area. This specimen was shot at night as it perched 15–20 m above the ground in the subcanopy of well­drained primary forest; its stomach was completely filled with a homogeneous, finely masticated, bright­green pulp. We surmise that the animal had been eating the new leaves of the tree in which it was shot because these had the same color and odor when crushed as the freshly dissected stomach contents.

Coendou prehensilis (Linnaeus)

Figure 71

Although we did not directly observe this species at Paracou, we found one of its distinctively large, tricolored quills on a dirt road near our camp. P. Petronelli (personal

commun., 1993) told us that he had also found quills of this species lying on the ground in our study area, and that an ocelot ( L. pardalis ) killed at Paracou by a local hunter several years before our inventory work began had quills of C. prehensilis embedded in its neck and shoulders. The species has occasionally been observed in roadside secondary growth by visiting researchers (G. Dubost, personal commun.), but accurate counts of such observations are unavailable.

DASYPROCTIDAE

The Paracou fauna contains two dasyproctids, one species each of Dasyprocta and Myoprocta , the usual number known to occur sympatrically throughout most of Amazonia. Although Guianan dasyproctids are easily identified in the field and in the museum, their technical names are still controversial due to unresolved issues of usage and synonymy. Large, edible, and diurnal, dasyproctids were among the first mammals of the Guianan fauna to be reported by European travellers, whose inadequate published de­ scriptions are at the root of several nomenclatural problems.

Figures

Fig. 53. Plantar views of left hindfeet of Oryzomys megacephalus (A, AMNH 266527), Oecomys auyantepui (B, AMNH 267595), and Rhipidomys nitela (C, AMNH 267583) illustrating diagnostic intergeneric differences. The hindfeet of Amazonian species of Oryzomys are proportionately narrow; the three central digits (II, III, and IV) are conspicuously longer than the outer digits (I and V); digit V is not opposable; the plantar epithelium is at least partially pigmented (grayish in fresh material); the plantar pads are small, hard, and more­or­less conical; and the skin between the pads is studded with small, scale­like tubercles. By contrast, the hindfeet of Oecomys and Rhipidomys are proportionately broader; digits I and V are longer relative to II–IV; digit V is semi­opposable; the plantar epithelium is usually entirely unpigmented (pinkish in fresh material); the plantar pads are larger, softer, cushion­like structures; and the skin between the plantar pads is smooth or creased but never tuberculate. Despite differences in hindfoot size and other features between the illustrated examples of O. auyantepui and R. nitela, their respective genera do not seem to be consistently distinguishable by pedal morphology.

Fig. 61. Caudal morphology of Rhipidomys venezuelae (A, AMNH 131081) and R. nitela (B, AMNH 267021). The tail of R. venezuelae is uniformly covered by short hairs that are clearly visible without magnification but do not conceal the underlying epidermal scales; there is no terminal tuft of conspicuously longer hairs. By contrast, the caudal hairs of R. nitela increase in length from the base of that organ to the tip, where the

Fig. 62. Posterior palatal morphology of Rhipidomys nitela (A, AMNH 267582) and Oecomys auyantepui (B, ROM 103244). In Rhipidomys (and other ‘‘thomasomyines’’; see Voss, 1993), the palate is said to be ‘‘short’’ because the mesopterygoid fossa (mpf) extends anteriorly to or between the last molars; additionally, posterolateral palatal pits (ppp) are small or absent in ‘‘thomasomyines’’. By contrast, the palate of Oecomys and other oryzomyines is said to be ‘‘long’’

Fig. 64. Dorsal, ventral, and lateral cranial views of NMW 42010, lectotype of Coendou melanurus

Fig. 65. Dorsal and ventral views of the skin of NMW 42010, lectotype of Coendou melanurus

Fig. 67. External morphology of Coendou melanurus (left, AMNH 266565) and C. insidiosus (right, AMNH 90119). Although these species are similar in possessing short bicolored quills concealed by long fur, C. melanurus has a much longer tail relative to head­and­body length, and its coarse blackish dorsal fur is heavily streaked with yellow­ or white­tipped guard hairs; the caudal bristles (covering the tail between its furry base and naked prehensile tip) are jet black. By contrast, C. insidiosus is relatively shorter­tailed and has softer smoky­gray (or whitish) dorsal fur without contrastingly colored guard hairs; the caudal bristles are brownish, not black. Both views approximately Χ0.3.

Fig. 68. Dorsal and ventral cranial views of Coendou melanurus (left, AMNH 94174) and C. insidiosus (right, AMNH 90119). All views approximately life­size.

Fig. 69. Left lateral cranial views of Coendou melanurus (top, AMNH 94174) and C. insidiosus

Fig. 70. Morphology of the roof of the external auditory meatus in Coendou melanurus (A, AMNH 266565) and C. insidiosus (B, AMNH 90119). In C. melanurus, the roof of the meatus has a prominent bony ridge (br) that is lacking in C. insidiosus. Scale bars = 1 mm.

Fig. 71. Unvouchered photographs of living Coendou melanurus (top) and C. prehensilis (bottom, not to same scale) from Petit Saut, French Guiana (ca. 28 km SSW Paracou). Both animals are alarmed, so the pale bases of their erected quills are exposed. When C. melanurus is not alarmed and defensive, its short bicolored (black­tipped) quills are hidden beneath a dense coat of long fur (see fig. 67). By contrast, the large tricolored (white­tipped) quills of C. prehensilis are always visible because the short sparse fur of this species is concealed among the quill bases. Also note the diagnostically bulging forehead and swollen muzzle of C. prehensilis, and the equally diagnostic blackish caudal bristles of C. melanurus. From color transparencies by J.­C. Vie´.