Microdelphys Burmeister, 1856

Pavan, Silvia E. & Voss, Robert S., 2016, A Revised Subgeneric Classification of Short-tailed Opossums (Didelphidae: Monodelphis), American Museum Novitates 2016 (3868), pp. 1-44 : 28-29

Subgenus Microdelphys Burmeister, 1856

TYPE SPECIES: Monodelphis tristriata ( Illiger, 1815) , an objective junior synonym of M. americana ( Müller, 1776) , by subsequent designation ( Thomas, 1888b).

CONTENTS: americana Müller, 1776 (including brasiliensis Erxleben, 1777; brasiliensis Daudin in Lacépède, 1802; rubida Thomas, 1899; trilineata Lund, 1840; tristriata Illiger, 1815 ; and umbristriata Miranda-Ribeiro, 1936 ); iheringi Thomas, 1888a ; scalops Thomas, 1888a (including theresa Thomas, 1921); and gardneri Solari et al., 2012 .

DIAGNOSIS: Dorsal body pelage usually marked with dark longitudinal stripes (but uniformly reddish in mature males of M. americana , and with grayish midbody contrasting with reddish head and rump in mature males of M. scalops ); ventral pelage uniformly colored, without self-whitish median markings. Mammae 4–1–4 = 9 to 8–1–8 = 17, all abdominalinguinal or abdominal-inguinal and pectoral. Thenar and first interdigital pads of hind foot separate; hypothenar pad of hind foot present or absent. Body pelage extends onto tail to about the same extent dorsally and ventrally; tail scales arranged in annular series. Infraorbital foramen usually dorsal to M1; frontal process of jugal well-developed and distinctly angular; parietal in contact with mastoid; incisive foramina long; maxillopalatine fenestra long; sphenorbital fissure large, basisphenoid laterally exposed; infratemporal crest of alisphenoid indistinct; secondary foramen ovale present or absent; tympanic wing of alisphenoid large; tip of anterior process of malleus not exposed on external surface of bulla; rostral tympanic process of petrosal broad and rounded, concealing fenestra cochleae in ventral view; stapes columelliform, imperforate or microperforate; subsquamosal foramen large. Anterior cingulids of m2 and m3 broad; entoconids of m1–m3 distinct; dp3 small and incompletely molariform (with bicuspid trigonid and indistinct anterior cingulid).

COMPARISONS: A dorsal pelage that includes three dark longitudinal stripes is unique to Microdelphys and is present in all member species, although it is lost ontogenetically in adult males of M. americana and M. scalops . Another feature that distinguishes Microdelphys from all other congeners is a well-developed and distinctly angular frontal process of the jugal.

Microdelphys additionally differs from Monodelphiops by having caudal scales in annular series, longer incisive foramina and maxillopalatine fenestrae, an indistinct infratemporal crest of the alisphenoid, a large alisphenoid tympanic wing, and a broadly rounded rostral tympanic process that conceals the fenestra cochleae in ventral view.

Comparisons of Microdelphys with other subgenera of Monodelphis have already been provided (see above).

REMARKS: As recognized in this report, Microdelphys includes “Clade C” and “Clade D” as recovered by the molecular analyses of Pavan et al. (2014). Although the sister-group relationship between clades C and D was not recovered by phylogenetic analyses based on mitochondrial sequence data (e.g., by Solari, 2010; Pavan et al., 2014; Vilela et al., 2015), compelling support for this relationship is provided by Bayesian analyses of multigene datasets (e.g., Pavan et al., 2016), and by the three-striped dorsal pelage pattern uniquely shared by juvenile and female specimens of all included species. An alternative nomenclatural solution would be to restrict Microdelphys to “Clade D” and to name a new subgenus for Monodelphis scalops (“Clade C”), but this seems unnecessary and would effectively discard important information about shared ancestry.

NOTES ON DISTRIBUTION AND SYMPATRY: Species of Microdelphys occur in forested areas of easternmost Para, in the Brazilian Atlantic Forest, in northeastern Argentina (Misiones), in some gallery forests of central and northeastern Brazil, and in the central Andes of Peru ( Solari et al., 2012; Pavan et al., 2014) ( table 3 ). Microdelphys is broadly sympatric with Monodelphiops in the southern Atlantic Forest, where these taxa have been collected together at several localities ( Pavan, 2015), and it also occurs sympatrically with species of Mygalodelphys and Monodelphis (see previous accounts).