INTRODUCTION

The genus Micronycteris Gray has traditionally included a heterogeneous array of small to medium-sized phyllostomines that shared little in common other than a short tail and a V-shaped pair of dermal pads on the chin (Sanborn, 1949; Koopman, 1993; Simmons, 1996). Simmons and Voss (1998) and Wetterer et al. (2000) concluded that this assemblage was not monophyletic, and argued that the subgenera of Micronycteris recognized by Simmons (1996) should be elevated to generic rank in order to achieve a phylogenetic classification. This change resulted in the recognition of four genera in addition to Micronycteris (sensu stricto): Glyphonycteris Thomas, Lampronycteris Sanborn, Neonycteris Sanborn, and Trinycteris Sanborn. So restricted, Micronycteris now includes eight species: hirsuta Peters, megalotis Gray, microtis Miller, brosseti Simmons and Voss, sanborni Simmons, schmidtorum Sanborn, minuta Gervais, and homezi Pirlot. Although no phylogenetic study to date has included all of these species, recent analyses of morphological data (Simmons, 1996; Wetterer et al., 2000) and DNA sequences (Baker et al., 2000) from various subsets of congeneric taxa suggest that Micronycteris (sensu stricto) is monophyletic.

As members of the phyllostomid subfamily Phyllostominae, species of Micronycteris are characterized by a moderately long rostrum and a well-developed nose leaf. Simmons and Voss (1998: 62) provided an emended diagnosis of the genus based on additional characters:

Although rarely captured in large numbers, species of Micronycteris constitute a large fraction of the gleaning-insectivorous bat fauna of Neotropical moist forests, where many species can occur sympatrically. Simmons and Voss (1998) recorded seven species of Micronycteris in a rainforested study area with a 3-km sampling radius at Paracou, French Guiana, and geographic range data suggest that similar numbers of congeners could coexist at most Amazonian localities. Several well-sampled local faunas include both dark-bellied species (hirsuta, megalotis, microtis) and pale-bellied forms (brosseti, sanborni, schmidtorum, minuta, homezi), but the ecobehavioral significance (if any) of this chromatic distinction is unknown. In fact, very little is known about the natural history of Micronycteris species, in large part because they are not commonly captured by mistnetting (the preferred bat-collecting method of most Neotropical mammalogists; Voss and Emmons, 1996).

In 1998 and 1999 we initiated a collaborative faunal inventory and ethnobiological research project on the Río Gálvez in the Amazonian lowlands of northeastern Peru. Among other voucher material collected to date, this project resulted in the preservation of 47 specimens representing 5 species of Micronycteris. One of those species is an undescribed dark-bellied form superficially resembling M. megalotis and M. microtis, but substantially larger than either of those taxa and differing from other known congeners by a unique combination of qualitative traits. We describe this new species below, document its diagnostic morphological attributes, and summarize our preliminary natural history observations in a comparative context.

METHODS

SYSTEMATICS

FAMILY PHYLLOSTOMIDAE GRAY, 1825

SUBFAMILY PHYLLOSTOMINAE GRAY, 1825

GENUS MICRONYCTERIS GRAY, 1866

Micronycteris matses, new species Figures 2, 3

Type Material:: The holotype (MUSM 15231), an adult male preserved in alcohol with the skull removed and cleaned, was collected at Nuevo San Juan by David W. Fleck (original number: DWF 782) on 9 November 1999. Seven paratypes include two additional males (AMNH 272814, 273133) and five females (MUSM 15229; AMNH 273043, 273044, 273095, 273196), all of which were likewise collected at Nuevo San Juan, between 27 June 1998 and 9 November 1999.

Distribution: Currently known only from the type locality (fig. 1), but perhaps widely distributed in Amazonia. Because few bats appear to be restricted by the riverine boundaries that limit the ranges of many nonvolant Amazonian mammals (Voss et al., 2001), it seems likely that the known distribution of Micronycteris matses is just an artifact of inadequate collecting, perhaps exacerbated by elusive roosting and foraging behavior.

Etymology: For the Matses, a Panoan-speaking indigenous population living along the Río Yavarí and its tributaries in northeastern Peru and western Brazil, treated as a noun standing in apposition to the generic name.

Diagnosis: A medium-sized species of Micronycteris (forearm 37.5–39.5 mm; weight 8–14 g) with dark-brown dorsal and ventral fur; dorsal hairs bicolored, 7–8 mm long in shoulder region, with white base comprising one-fourth or less of each hair; fur on outside of medial third of pinna short (≤ 3 mm) and dense; pinnae large with rounded tips, connected across crown of head by low interauricular band with shallow midline notch; thumb small (9.5–11 mm); second phalanx of wing digit IV shorter than first; calcar longer than foot; mastoid breadth less than zygomatic breadth; crown height of upper incisors not reduced; no gap present between outer upper incisor and canine; P3 and P4 subequal in anteroposterior length, height of P3 equal to or slightly less than that of P4; P4 with small lingual heel and variably developed lingual cusp; M1 narrower than M2; no noticeable gap between posterior edge of cingulum of M2 and anterolingual edge of M3 when toothrow seen in occlusal view; lower incisors small and bilobed, not markedly hypsodont, crown height one and one-half to two times crown width; lower premolar dentition with p2 largest in anteroposterior length and height, p3 smallest in both dimensions; coronoid process high, upper margin of ascending process with steep slope (25–30°).

Of the characters listed above, five are particularly useful for field identification of Micronycteris matses: size (forearm 37.5–39.5 mm; weight 8–14 g); ventral fur color (dark brown, similar to dorsal fur); length of the fur on the leading edge of the pinna (short, ≤ 3 mm); morphology of the interauricular band (low, with shallow midline notch); and morphology of the lower incisor crowns (not markedly hypsodont). Within the genus Micronycteris, this combination of traits is unique to M. matses.

Measurements: Dimensions of each specimen in the type series of Micronycteris matses are provided in table 1, and metrical comparisons with representative series of other dark-bellied congeners are summarized in table 2.

Description and Comparison: Micronycteris matses is a medium-sized member of the genus, smaller than hirsuta but larger than microtis and megalotis (tables 1–3). From all other dark-bellied congeners, matses can be unambiguously distinguished on the basis of forearm length, greatest length of skull, condylo-incisive length, postorbital breadth, mastoid breadth, zygomatic breadth, maxillary toothrow length, and breadth across molars. Additionally, matses can be distinguished from hirsuta on the basis of total length, tibia length, and thumb length; from microtis on the basis of weight and total length; and from megalotis on the basis of weight, hindfoot length, and tibia length. Micronycteris matses is larger than all pale-bellied congeners (brosseti, schmidtorum, homezi, minuta, sanborni; see measurements summarized by Simmons [1996] and Simmons and Voss [1998]) in most anatomical dimensions.

As in all Micronycteris, the dorsal pelage of matses is composed of bicolored hairs with white bases and brown tips. In the upper back region, the white base comprises no more than one-fourth of the length of each hair. This is comparable to the pattern seen in hirsuta, but differs from that seen in most other species. The white bases comprise between one-fourth and one-half of each hair on the upper back in microtis, megalotis, brosseti, schmidtorum, and homezi, and are even more extensive in minuta (comprising one-half to two-thirds of each hair) and sanborni (two-thirds to three-fourths of each hair). The length of the dorsal fur over the upper back in matses is approximately 7–8 mm, comparable to that of microtis, brosseti, and homezi. In contrast, minuta and sanborni have shorter fur over the shoulders (5–7 mm), whereas megalotis, schmidtorum, and hirsuta have longer fur (8–11 mm in the former two species, 11–14 mm in the latter).

The ventral fur of matses (including that covering the neck and throat) is brown, approximately the same shade as the dorsal fur. This is the same pattern seen in megalotis, microtis, and hirsuta. By contrast, the ventral fur of brosseti, schmidtorum, homezi, and minuta is gray or buff (paler than the dorsal fur), and the ventral fur of sanborni is bright white.

The fur on the leading edge of the medial third of each pinna is short (≤ 3 mm) and dense in matses, similar to the condition seen in microtis, minuta, hirsuta, brosseti, and sanborni. By contrast, the auricular fur of megalotis, schmidtorum, and homezi is much longer (5–8 mm). As in all other species of Micronycteris, the ears of matses are connected across the crown of the head by an interauricular band of skin. In matses, this band is low and nearly horizontal in profile, and is marked at the midline by a shallow notch; a similar condition is seen in all other dark-bellied congeners. This morphology contrasts sharply with the interauricular band seen in most pale-bellied species (i.e., schmidtorum, minuta, sanborni, and homezi), which is higher and divided by a deep median notch into two roughly triangular flaps.

The second phalanx of wing digit IV is shorter than the first in matses, as it is also in megalotis, microtis, hirsuta, brosseti, schmidtorum, and homezi. By contrast, the first and second phalanges of digit IV are subequal in minuta and sanborni.

The calcar is distinctly longer than the hind foot in matses, as it is in most other species of Micronycteris. In contrast, the calcar is approximately equal in length to the hind foot in sanborni, and is markedly shorter than the foot in minuta and homezi.

As noted by Simmons (1996), cranial morphology is remarkably similar in all species of Micronycteris. Like other members of the genus, matses has a relatively long rostrum, no anteorbital inflation, a large braincase, and shallow basisphenoid pits (fig. 2). Mastoid breadth is less than zygomatic breadth in matses, as it is in most other Micronycteris species. By contrast, mastoid breadth is greater than zygomatic breadth in sanborni, minuta, and homezi.

Like all other congeneric species, Micronycteris matses has a dental formula of I 2/2, C 1/1, P 2/3, M 3/3 × 2 = 34. The crown height of the upper incisors is not reduced, and no gap is present between the outer upper incisor and the canine. In this respect matses resembles most other species of Micronycteris, the contrasting morphology being seen only in sanborni (in which crown height of I2 is reduced and a gap is present between this tooth and the canine; Simmons, 1996).

Although differences in the upper premolar dentition are subtle, variation in this region provides an important means of distinguishing species of Micronycteris (see Simmons, 1996). In matses, P3 and P4 are subequal in length (anteroposterior dimension), and the height (dorsoventral dimension) of P3 is either equal to or very slightly less than that of P4 (fig. 2). This is similar to the condition seen in most other congeners, but P3 is noticeably smaller than P4 in both length and height in minuta and sanborni.

The degree of development of the posterolingual heel and lingual cusp on P4 varies among and within species of Micronycteris. The lingual heel of P4 in matses is similar in outline and proportions to the homologous structures seen in megalotis, microtis, brosseti, schmidtorum, and homezi. By contrast, the lingual heel is proportionately smaller in hirsuta and minuta, and larger in sanborni (see illustrations in Simmons [1996] and Simmons and Voss [1998]). The lingual cusp of P4, which is formed from the raised edge of the heel, is variably developed in matses, as it is likewise in microtis and megalotis. The lingual cusp is present and tapers to a sharp point (which typically bears a wear facet) in most individuals, but is poorly developed (or lacking entirely) in others. By contrast, the lingual cusp is never well developed and always lacks a sharp point in brosseti, homezi, minuta, and sanborni, and it is entirely lacking in many specimens of schmidtorum. The lingual cusp of P4 in hirsuta is located farther posteriorly than in the other species; typically well developed, it tapers to a blunt point that is not marked by a wear facet.

The first upper molar is noticeably narrower than M2 in matses, as it is in most other species of Micronycteris. Uniquely, however, the lingual portion of M1 is expanded so that M1 and M2 are subequal in width in sanborni, which also differs from all other congeners in having a large gap between the posterior edge of the cingulum of M2 and the anterolingual edge of M3 when the toothrow is observed in occlusal view.

As in most other species of Micronycteris, the lower incisors of matses are small and bilobed, with the height of the anterior face of each incisor crown between one and one-half to two times the width of the crown. This differs markedly from the condition observed in hirsuta, which has uniquely hypsodont lower incisors crowns, the heights of which are roughly three times their widths (fig. 3).

The lower premolar dentition of matses most closely resembles that of hirsuta. In both of these species, p2 is the largest premolar in both anteroposterior length and dorsoventral height, p3 is the smallest in both dimensions, and p4 is intermediate (fig. 2). By contrast, p3 is relatively larger (approximately the same size as p4) in both microtis and megalotis; in these taxa, p2 is often slightly larger than either p3 or p4, although there is some within-species variation in this trait (all three lower premolars are subequal in some individuals). In brosseti and schmidtorum, p2 and p4 are subequal in length and in height, whereas p3 is slightly smaller in both dimensions. In minuta, sanborni, and homezi, p3 is further reduced relative to p2 and p4, which are large and subequal.

The coronoid process in Micronycteris matses is high, and the upper margin of the ascending process has a steep slope (25–30°), similar to the mandibular morphology of megalotis, microtis, brosseti, and schmidtorum. By contrast, the coronoid process is comparatively low and the upper margin of the ascending ramus has a shallow slope (16–18°) in minuta, sanborni, and homezi.

NATURAL HISTORY

Of the eight known specimens of Micronycteris matses, one was caught in a ground-level mistnet at dusk (18:00 hrs) in well-drained primary rainforest on 27 June 1998. The remaining seven specimens were all taken from diurnal roosts as described in the following abstracts from Fleck's 1999 fieldnotes (numbers refer to entries in a catalog of bat roosts):

Several aspects of these scant field data are noteworthy. First, our capture records for Micronycteris matses (one in mistnets, seven at roosts) are similar to the pattern we recorded for other congeneric species at Nuevo San Juan and elsewhere in Amazonia (table 4). In general, species of Micronycteris are more commonly encountered by searching for diurnal roosts than by mistnetting, a fact that perhaps accounts for the small numbers of these bats routinely taken by inventory workers who rely principally on the latter method to sample Neotropical chiropteran faunas. The adoption of intensive roost-searching protocols by future inventory projects will doubtless result in more captures of M. matses, which is perhaps widely distributed in Amazonia.

Second, the four roosts found to be occupied by Micronycteris matses at Nuevo San Juan were all essentially similar (holes in the ground), and unlike those typically used by most other congeneric species (table 5). All of the roosts occupied by M. matses were probably excavated (or enlarged) by the giant long-nosed armadillo (Dasypus kappleri), an important game species esteemed by the Matses, who identify stream headwater gullies as a favored site for burrow construction (Fleck and Harder, 2000). By contrast, no other Micronycteris species used this type of roost exclusively at Nuevo San Juan, and none used such refugia at Paracou, another Amazonian locality where we found many Micronycteris roosts. Roosts typically inhabited by other congeneric species are rotted cavities in logs or standing trees, but M. microtis was sometimes found in holes in the ground (usually armadillo burrows) at Nuevo San Juan.

Lastly, we note that Micronycteris matses occupies the conspicuous size hiatus remarked by Simmons and Voss (1998: 65), which previously distinguished M. hirsuta from all of its diminutive congeners. The size spectrum of Amazonian Micronycteris now appears to consist of a more evenly graded series of taxa, each of which perhaps exploits some distinctive range of trophic (or other) resources. How (or if) sympatric Micronycteris species differ from one another by partitioning one or more crucial niche dimensions, however, is a topic that remains to be addressed by future field studies.