Gracilinanus Gardner and Creighton, 1989

Voss, RS & Jansa, SA, 2009, Phylogenetic Relationships And Classification Of Didelphid Marsupials, An Extant Radiation Of New World Metatherian Mammals, Bulletin of the American Museum of Natural History 2009 (322), pp. 1-177 : 128-131

Gracilinanus Gardner and Creighton, 1989 Figure 50

CONTENTS: aceramarcae Tate, 1931 ; agilis Burmeister, 1854 (including beatrix Thomas, 1910; buenavistae Tate, 1931; and peruana Tate, 1931); dryas Thomas, 1898 ; emiliae Thomas, 1909 (including longicaudus Hershkovitz, 1992); marica Thomas, 1898 (including perijae Hershkovitz, 1992); and microtarsus Wagner (1842) .

MORPHOLOGICAL DESCRIPTION: Combined length of adult head and body ca. 75– 130 mm; adult weight ca. 10–50 g. Rhinarium with two ventrolateral grooves on each side of median sulcus; dark circumocular mask present; pale supraocular spot absent; dark midrostral stripe absent; throat gland present in adult males. Dorsal pelage unpatterned reddish or grayish brown with dark-gray hair bases; dorsal guard hairs short and inconspicuous; ventral fur mostly gray-based buff or orange (e.g., in G. microtarsus ), but self-white in some species (e.g., G. emiliae ). Manus paraxonic (dIII 5 dIV); manual claws small, not extending beyond fleshy apical pads of digits; dermatoglyph-bearing manual plantar pads present; central palmar epithelium smooth or sparsely tuberculate; lateral carpal tubercles present in fully adult males, but medial carpal tubercles absent in both sexes. Pedal digits unwebbed; dIV longer than other pedal digits; plantar surface of heel naked. Pouch absent; mammary formula (unknown for most species) 3–1–3 5 7 to 4–1–4 5 9; cloaca present. Tail much longer than combined length of head and body, slender and muscular (not incrassate), and macroscopically naked (furred only near base); naked caudal integument usually unicolored (dark) but sometimes indistinctly bicolored (dark above, paler below) at base; caudal scales in annular series (most species) or annular and spiral series ( G. emiliae ), each scale with three subequal bristlelike hairs emerging from distal margin; ventral caudal surface modified for prehension distally (with naked median groove and apical pad bearing dermatoglyphs).

Premaxillary rostral process present. Nasals long, extending anteriorly beyond I1 (concealing nasal orifice from dorsal view), and conspicuously widened posteriorly near maxillary-frontal suture. Maxillary turbinals elaborately branched. Two lacrimal foramina present on each side but usually inconspicuous in lateral view (partially concealed within anterior orbital margin). Interorbital region more or less parallel-sided, without welldeveloped constrictions; supraorbital margins smoothly rounded in most species (e.g., G. dryas ) or with well-developed beads (in G. emiliae ); postorbital processes usually absent except in large adult specimens of G. microtarsus . Left and right frontals and parietals separated by persistent median sutures. Parietal and alisphenoid in contact on lateral braincase (no squamosal-frontal contact). Sagittal crest absent. Petrosal laterally exposed through fenestra in parietal-squamosal suture. Parietal-mastoid contact present (interparietal does not contact squamosal).

Maxillopalatine fenestrae present; palatine fenestrae present; maxillary fenestrae present in most species (but very small and occasionally absent uni- or bilaterally in G. emiliae ); posterolateral palatal foramina small, not extending lingual to M4 protocones; posteri- or palatal morphology conforms to Didelphis morphotype (with well-developed lateral cor- ners, the choanae constricted behind). Maxillary and alisphenoid not in contact on floor of orbit (separated by palatine). Transverse canal foramen present. Alisphenoid tympanic process flask shaped or globular (not laterally compressed and without a well-developed ventral process), almost always with anteromedial strut enclosing extracranial course of mandibular nerve (secondary foramen ovale usually present), and not contacting rostral tympanic process of petrosal. Anterior limb of ectotympanic directly suspended from basicranium. Stapes triangular, with large obturator foramen. Fenestra cochleae usually exposed (partially concealed by caudal tympanic process of petrosal in some specimens of G. aceramarcae and G. microtarsus ). Paroccipital process small, rounded, and adnate to petrosal. Dorsal margin of foramen magnum bordered by exoccipitals and supraoccipital, incisura occipitalis present.

Two mental foramina present on lateral surface of each hemimandible; angular process acute and strongly inflected.

Unworn crowns of I2–I5 symmetrically rhomboidal (‘‘premolariform’’), with subequal anterior and posterior cutting edges, increasing in length (mesiodistal dimension) from I2 to I5 (e.g., in G. microtarsus ), or I2– I5 crowns subequal in length (e.g., in G. emiliae ). Upper canine (C1) alveolus in premaxillary-maxillary suture; C1 simple, without accessory cusps except in G. emiliae (which consistently has a posterior accessory cusp). First upper premolar (P1) smaller than posterior premolars but well-formed and not vestigial; second and third upper premolars (P2 and P3) subequal in height; P3 with posterior cutting edge only; upper milk premolar (dP3) large and molariform. Molars carnassialized (postmetacristae longer than postprotocristae); relative widths M1, M2, M3. M4 or M1, M2, M3, M4; centrocrista strongly inflected labially on M1–M3; ectoflexus indistinct or absent on M1 and M2 but consistently distinct on M3; anterolabial cingulum continuous with preprotocrista (complete anterior cingulum present) on M3; postprotocrista without carnassial notch. Last upper tooth to erupt is P3.

Lower incisors (i1–i4) with distinct lingual cusps. Second lower premolar (p2) taller than p3; lower milk premolar (dp3) trigonid incomplete (unicuspid in the few specimens we were able to score for this trait). Hypoconid labially salient on m3; hypoconulid twinned with entoconid on m1–m3; entoconid taller than hypoconulid on m1–m3.

DISTRIBUTION: Species of Gracilinanus occur in tropical and subtropical moist forests in lowland and montane landscapes (to at least 3350 m; Voss et al., 2004b: table 12) from northern Venezuela to Bolivia, Paraguay, southeastern Brazil, northeastern Argentina, and northern Uruguay ( D’Elía and Martínez, 2006; Teta et al., 2007; Creighton and Gardner, 2008a). Apparently, only one Argentinian record and two Uruguayan records of Gracilinanus are valid, the remaining published localities for this genus from both countries having been based on specimens of Cryptonanus (see Voss et al., 2005; D’Elía and Martínez, 2006; Teta et al., 2007). Gracilinanus is said not to occur in central Amazonia ( Patton and Costa, 2003), but the species to be expected there ( G. emiliae ) is difficult to collect and this distributional hiatus is perhaps an artifact of inadequate faunal sampling.30

REMARKS: The contents of this genus have changed significantly in the years since it was first described by Gardner and Creighton (1989), principally by removal of distantly related forms to new genera (see Voss et al., 2005: table 1). With the exception of Gracilinanus microtarsus and G. agilis , species of this genus are not common in museum collections, and geographic distributions remain poorly documented. In addition, current species concepts will doubtless change as more information becomes available. For example, molecular data (summarized by Costa et al., 2003) suggest the presence of an undescribed, morphologically cryptic species among the material currently identified as G. microtarsus ; the geographic distribution of material currently identified as G. emiliae is improbably broad; and some specimens from northern Colombia and eastern Peru do

30 All of the central Amazonian records of Gracilinanus emiliae mapped by Hershkovitz (1992b: fig. 1) and Brown (2004: fig. 20) are either based on misidentified material or specimens that have yet to be examined for reliably diagnostic traits ( Voss et al., 2001: 29–30).

not resemble any currently recognized taxa. Therefore, the species-level diversity of Gracilinanus seems certain to increase with future revisionary research.

The monophyly of Gracilinanus in its currently restricted sense is strongly support- ed by parsimony, likelihood, and Bayesian analyses of RAG1 (fig. 30), BRCA1 (fig. 31), vWF (fig. 32), concatenated sequence data from five genes (fig. 33), and combined datasets that include both nonmolecular and molecular characters (figs. 35, 36); it is also moderately supported by parsimony and likelihood analyses of IRBP (fig. 28). We have no plausible explanation as to why analyses of DMP1 strongly support the conflicting hypothesis that G. emiliae is the sister taxon of Cryptonanus (fig. 29). Although Gracilinanus is recovered as a clade by parsimony analysis of nonmolecular data (fig. 27), only two morphological traits optimize as unambiguous generic synapomorphies (appendix 5).