taxonID	type	description	language	source
F964F917F3040673FCE7852C562B23DE.taxon	materials_examined	TYPE SPECIES: Didelphis (Micoureus) canescens Allen, 1893, subsequently transferred to Marmosa by Allen (1897) and thereafter known as Marmosa canescens throughout the 20 th century mammalogical literature (e. g., by Tate, 1933; Gardner, 1993). GEOGRAPHIC DISTRIBUTION: Apparently endemic to Mexico, where it occurs in seasonally dry (deciduous) tropical forests from Sonora southward (principally along the Pacific littoral and adjacent slopes of the coastal cordilleras) to Oaxaca and Chiapas; isolated populations also occur in the northern part of the Yucatan Peninsula and on the Tres Marías Islands (Hall, 1981; Wilson, 1991; Reid, 1997). Armstrong and Jones (1971) implied that T. canescens occurs in Guatemala, but we have not examined specimens from that country, nor have we seen any published references to vouchered Guatemalan records.	en	VOSS, ROBERT S., JANSA, SHARON A. (2003): Phylogenetic Studies On Didelphid Marsupials Ii. Nonmolecular Data And New Irbp Sequences: Separate And Combined Analyses Of Didelphine Relationships With Denser Taxon Sampling. Bulletin of the American Museum of Natural History 2003 (276): 1-82, DOI: 10.1206/0003-0090(2003)276<0001:PSODMI>2.0.CO;2, URL: http://www.bioone.org/doi/abs/10.1206/0003-0090%282003%29276%3C0001%3APSODMI%3E2.0.CO%3B2
F964F917F3040673FCE7852C562B23DE.taxon	description	CONTENTS: Only a single valid species is currently recognized following Tate (1933) and Gardner (1993), who treated gaumeri Osgood (1913), insularis Merriam (1898), oaxacae Merriam (1897), and sinaloae Allen (1898) as synonyms or subspecies of canescens. However, substantial geographic variation has been noted by authors (e. g., Wilson, 1991), and sufficient material (amounting to several hundred specimens in U. S. and Mexican museums) is now available for a long­overdue critical revision of these nominal taxa. Among them, the status of the Yucatecan population (gaumeri) merits particular attention due to its zoogeographically unusual disjunction from supposedly conspecific western Mexican forms (see Remarks, below).	en	VOSS, ROBERT S., JANSA, SHARON A. (2003): Phylogenetic Studies On Didelphid Marsupials Ii. Nonmolecular Data And New Irbp Sequences: Separate And Combined Analyses Of Didelphine Relationships With Denser Taxon Sampling. Bulletin of the American Museum of Natural History 2003 (276): 1-82, DOI: 10.1206/0003-0090(2003)276<0001:PSODMI>2.0.CO;2, URL: http://www.bioone.org/doi/abs/10.1206/0003-0090%282003%29276%3C0001%3APSODMI%3E2.0.CO%3B2
F964F917F3040673FCE7852C562B23DE.taxon	etymology	ETYMOLOGY: From the Nahuatl (Aztec) word for ‘‘ opossum’ ’ (Karttunen, 1983), which is still in colloquial use as a singular masculine noun (e. g., by Villa­Ramírez, 1991).	en	VOSS, ROBERT S., JANSA, SHARON A. (2003): Phylogenetic Studies On Didelphid Marsupials Ii. Nonmolecular Data And New Irbp Sequences: Separate And Combined Analyses Of Didelphine Relationships With Denser Taxon Sampling. Bulletin of the American Museum of Natural History 2003 (276): 1-82, DOI: 10.1206/0003-0090(2003)276<0001:PSODMI>2.0.CO;2, URL: http://www.bioone.org/doi/abs/10.1206/0003-0090%282003%29276%3C0001%3APSODMI%3E2.0.CO%3B2
F964F917F3040673FCE7852C562B23DE.taxon	diagnosis	DIAGNOSIS AND COMPARISONS: Small didelphines that can be distinguished from all oth­ er members of the subfamily by nonmolecular characters analyzed in this report, among which the following are salient points of morphological comparison. Rhinarium with two ventrolateral grooves; dark ocular mask present; supraocular spots absent; gular gland absent; dorsal fur unpatterned (unicolored grayish or reddish­gray), with short, inconspicuous guard hairs; manual digits III and IV subequal; large adult males with well­developed lateral carpal tubercles but not medial carpal tubercles; plantar surface of hind foot naked from heel to toes; pedal digit IV longer than other pedal digits; marsupium absent; tail essentially naked (without a conspicuously furred base), covered by epidermal scales in annular series except for distal prehensile surface, not incrassate. Rostral process of premaxillae absent; nasals conspicuously wider posteriorly than anteriorly; very large, flattened, wing­like postorbital processes present in mature adults; sagittal crest absent; parietal and alisphenoid in contact on lateral braincase; no lateral petrosal exposure through fenestra between parietal and squamosal; maxillopalatine fenestrae long (usually extending from the level of P 3 to M 3); palatine fenestrae absent; maxillary fenestrae present, often confluent with maxillopalatine openings; posterolateral palatal foramina posterior to M 4 protocones; posterior palate with prominent lateral corners, the internal choanae constricted behind; transverse canal foramen present; secondary foramen ovale absent; ectotympanic suspension direct; fenestra cochleae exposed; paroccipital process of exoccipital small, round­ ed, adnate to posterior aspect of petrosal; dorsal margin of foramen magnum formed by supraocciptal and exoccipitals. Crowns of I 2 – I 5 symmetrically rhomboidal and subequal (not increasing in size from front to back); P 2 and P 3 subequal in height; P 3 without an anterior cutting edge; upper molars strongly dilambdodont; distinct ectoflexus present on M 2 and M 3 (much deeper on the latter tooth); anterior cingulum complete on M 3. Distinct lingual cusp present on i 1 – i 4; c 1 an erect, dorsally recurved tooth (not procumbent and premolariform); p 2 much taller than p 3; dp 3 with incomplete (bicuspid) trigonid; entoconid a tall sharp cusp, much higher than hypoconulid on m 1, m 2, and sometimes m 3.	en	VOSS, ROBERT S., JANSA, SHARON A. (2003): Phylogenetic Studies On Didelphid Marsupials Ii. Nonmolecular Data And New Irbp Sequences: Separate And Combined Analyses Of Didelphine Relationships With Denser Taxon Sampling. Bulletin of the American Museum of Natural History 2003 (276): 1-82, DOI: 10.1206/0003-0090(2003)276<0001:PSODMI>2.0.CO;2, URL: http://www.bioone.org/doi/abs/10.1206/0003-0090%282003%29276%3C0001%3APSODMI%3E2.0.CO%3B2
F964F917F3040673FCE7852C562B23DE.taxon	discussion	REMARKS: Tlacuatzin canescens is part of a distinctive fauna that inhabits dry tropical forests in western Mexico. Recent syntheses of distributional data have documented the impressive diversity of western Mexican dry forests, to which at least 25 mammalian species are endemic (Ceballos, 1995; Ceballos and García, 1995; Ceballos et al., 1998). A different fauna inhabits the dry tropical forests of the Yucatan Peninsula, however, where T. canescens also occurs. The Yucatecan dry forest fauna is less easily defined than that of western Mexico because dry forest on the Yucatan Peninsula grades into more mesic vegetation formations, but most Yucatecan endemics are primarily dry­forest species (e. g., Heteromys gaumeri, Otonyctomys hatti, Mazama pandora; see Reid, 1997; Medellín et al., 1998). Tlacuatzin is one of seven mammalian genera endemic to Mesoamerican dry forests, the other six consisting of a shrew (Megasorex), one bat (Musonycteris), and four rodents (Hodomys, Osgoodomys, Otonyctomys, Xenomys). Without exception, all of these genera are currently considered to be monotypic (Wilson and Reeder, 1993). Whereas five are endemic to western Mexico (Megasorex, Musonycteris, Hodomys, Osgoodomys, Xenomys) and one is endemic to the Yucatan Peninsula (Otonyctomys), only Tlacuatzin has a disjunct distribution in both dry­forest regions. In fact, Tlacuatzin appears to be one of only two mammalian taxa (of any rank) endemic to Middle American dry forests that occurs both in western Mexico and the Yucatan, a biogeographic anomaly that begs critical attention. 13	en	VOSS, ROBERT S., JANSA, SHARON A. (2003): Phylogenetic Studies On Didelphid Marsupials Ii. Nonmolecular Data And New Irbp Sequences: Separate And Combined Analyses Of Didelphine Relationships With Denser Taxon Sampling. Bulletin of the American Museum of Natural History 2003 (276): 1-82, DOI: 10.1206/0003-0090(2003)276<0001:PSODMI>2.0.CO;2, URL: http://www.bioone.org/doi/abs/10.1206/0003-0090%282003%29276%3C0001%3APSODMI%3E2.0.CO%3B2
