Thylamys Gray, 1843

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 : 138-141

Thylamys Gray, 1843 Figure 54

CONTENTS: cinderella Thomas, 1902 (including sponsorius Thomas, 1921); elegans Waterhouse, 1839 (including coquimbensis Tate, 1931; and soricinus Philippi, 1894); karimii Petter, 1968 ; macrurus Olfers, 1818 (including griseus Desmarest, 1827); pallidior Thomas, 1902 ; pusillus Desmarest, 1804 (including bruchi Thomas, 1921; citellus Thomas, 1912; nanus Olfers, 1818; and verax Thomas, 1921); tatei Handley, 1957 ; velutinus Wagner, 1842 (including pimelurus Reinhardt, 1851); and venustus Thomas, 1902 (including janetta Thomas, 1926).

MORPHOLOGICAL DESCRIPTION: Combined length of adult head and body ca. 75– 140 mm; adult weight ca. 10–65 g. Rhinarium with two ventrolateral grooves on each side of median sulcus in most examined species (but T. pallidior has only a single ventrolateral groove on each side); dark circumocular mask present; pale supraocular spot absent; dark midrostral stripe absent; throat gland present in fully adult males, and apparently also in adult females of some species ( Carmignotto and Monfort, 2006). Dorsal pelage usually grayish and distinctly darker middorally than laterally (‘‘tricolored’’), but dorsal fur brownish and without conspicuous patterning in T. karimii and T. velutinus ( Carmignotto and Monfort, 2006) ; dorsal hair bases dark gray; dorsal guard hairs short and inconspicuous; ventral fur self-white in some species (e.g., T. pusillus ), wholly or partly gray-based whitish or yellowish in others (e.g., T. venustus ). Manus mesaxonic (dIII. dIV); manual claws about as long as fleshy apical pads in most species (but claws extend well beyond apical pads in T. karimii and T. velutinus ; Carmignotto and Monfort, 2006); dermatoglyph-bearing manual plantar pads present in most species; central palmar epithelium densely covered with small convex tubercles; carpal tubercles absent in both sexes. Pedal digits unwebbed; dIV longer than other pedal digits; plantar surface of heel coarsely furred. Pouch absent; mammae varying among species from 4–1–4 5 9 (in T. karimii ; Carmignotto and Monfort, 2006) to 7–1–7 5 15 (in T. elegans ; Tate, 1933), including ‘‘pectoral’’ teats (when the total number of mammae $ 11); cloaca present. Tail longer than combined length of head and body in most species (except in T. karimii and T. velutinus ; Carmignotto and Monfort, 2006); apparently always incrassate (but quantity of stored fat may vary seasonally); furred only at base (to about the same extent dorsally as ventrally); unfurred caudal integument bicolored (dark above, pale below) in most species and parti-colored in some ( T. macrurus has an all-white tail tip); tail scales in annular series, 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) in most species, but ventral prehensile surface reduced or absent in T. karimii and T. velutinus ( Carmignotto and Monfort, 2006) .

Premaxillary rostral process absent. Nasals long, extending anteriorly above or beyond I1 (concealing nasal orifice in dorsal view), and uniformly narrow (with subparallel lateral margins) in most specimens. Maxillary turbinals elaborately branched. Two lacrimal foramina present on each side, exposed to lateral view on anterior orbital margin in most species, but usually concealed inside orbit in others (e.g., T. tatei ). Interorbital and postorbital constrictions often distinct; supraorbital margins rounded in some species (e.g., T. pallidior ), squared or beaded in others; postorbital processes usually absent or indistinct but occasionally present in old adults of some species (e.g., T. macrurus ). Left and right frontals and parietals separat- ed by persistent median sutures. Parietal and alisphenoid in contact on lateral braincase (no frontal-squamosal contact). Sagittal crest absent. Petrosal almost always exposed laterally 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 some species (e.g., T. pusillus ) but absent in others (e.g., T. pallidior ); posterolateral palatal foramina very large, extending anteriorly between M4 protocones; posterior palatal morphology conforms to Didelphis morphotype (with prominent lateral corners, the choanae constricted behind). Maxillary and alisphenoid not in contact on floor of orbit (separated by palatine). Transverse canal foramen present. Alisphenoid tympanic process smoothly globular, with anteromedial process enclosing extracranial course of mandibular nerve (secondary foramen ovale 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 concealed in sinus formed by rostral and caudal tympanic processes of petrosal. Paroccipital process small, rounded, adnate to petrosal. Dorsal margin of foramen magnum bordered by supraoccipital and exoccipitals, 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. Upper canine (C1) alveolus in premaxillary-maxillary suture; C1 without accessory cusps in all examined species (but see Carmignotto and Monfort, 2006).33 First upper premolar (P1) smaller than posterior premolars but well formed and not vestigial; third upper premolar (P3) taller than P2; P3 with posterior cutting edge only; upper milk premolar (dP3) large, molariform, and nonvestigial. Molars strongly carnassialized (postmetacristae much longer than postprotocristae); relative widths usually M1, M2, M3, M4; centrocrista strongly inflected labially on M1–M3; ectoflexus absent or indistinct on M1, usually present but shallow on M2, consistently deep and distinct on M3; anterolabial cingulum and preprotocrista discontinuous (anterior cingulum incomplete) on M3; postprotocrista without carnassial notch. Last upper tooth to erupt is P3.

Lower incisors (i1–i4) with distinct lingual cusps. Second and third upper premolars (p2 and p3) subequal in height; lower milk premolar (dp3) trigonid usually incomplete (bicuspid). Hypoconid labially salient on m3; hypoconulid twinned with entoconid on m1– m3; entoconid much taller than hypoconulid on m1–m3.

DISTRIBUTION: Species of Thylamys collectively range from north-central Peru (Ancash) southward along the Andes and Pacific coastal lowlands to central Chile; in the unforested landscapes south of Amazonia, the genus extends eastward across Bolivia ( Anderson, 1997), Paraguay, and Argentina ( Flores et al., 2007) to Uruguay ( González et al., 2000) and eastern Brazil (Bahia, Pernambuco, and Piauí; Carmignotto and Monfort, 2006). Recorded elevations range from near sea level to at least 3800 m ( Solari, 2003).

REMARKS: The monophyly of Thylamys is strongly supported by parsimony, likelihood, and Bayesian analyses of IRBP (fig. 28), BRCA1 (fig. 31), vWF (fig. 32), and concatenated sequence data from five genes (fig. 33). Strong support for this clade is also

33 Although several Brazilian species of Thylamys were scored as polymorphic for presence of posterior accessory canine cusps by Carmignotto and Monfort (2006: table 4), the increasing frequencies that they observed in older age classes suggest that C 1 in these taxa is notched by occlusion with p 1 in their material, and that the structure in question is not homologous with the posterior accessory cusp scored from specimens with unworn dentitions by Voss and Jansa (2003: character 53).

provided by parsimony and likelihood analyses of DMP1 (fig. 29) and by parsimony and Bayesian analyses of RAG1 (fig. 30) and combined datasets that include both nonmolecular and molecular characters (figs. 35, 36). The monophyly of Thylamys is also recovered with moderate support by parsimony analysis of nonmolecular characters (fig. 27), but only one morphological trait (uniformly narrow nasals; see appendix 5) optimizes as an unambiguous generic synapomorphy.

We tentatively recognize bruchi as a synonym of Thylamys pusillus following Voss et al. (in press), who explain why the former name does not belong in the synonymy of T. pallidior (contra Creighton and Gardner, 2008c), and we refer sponsorius to the synonymy of T. cinderella following Braun et al., (2005). The names pulchellus Cabrera, 1934, and fenestrae Marelli, 1932, might be synonyms of T. pusillus and T. pallidior , respectively, but we have not seen the holotypes and published information about these nominal taxa is insufficient to support any definite conclusions about them. Many other species-level issues in this genus remain problematic despite much recent taxonomic work (e.g., Palma et al., 2002; Solari, 2003; Braun et al., 2005; Carmignotto and Monfort, 2006).