A Revised Subgeneric Classification of Short-tailed Opossums (Didelphidae: Monodelphis) Author Pavan, Silvia E. Author Voss, Robert S. text American Museum Novitates 2016 2016-12-01 2016 3868 1 44 http://www.bioone.org/doi/10.1206/3868.1 journal article 5850 10.1206/3868.1 30c2369a-9306-4504-b02e-1040172cf041 0003-0082 4598434 Subgenus Monodelphiops Matschie, 1916 TYPE SPECIES : Monodelphis sorex ( Hensel, 1872 ) , a subjective junior synonym of Monodelphis dimidiata ( Wagner, 1847 ) , by original designation. SYNONYMS: Minuania Cabrera, 1919 . CONTENTS: dimidiata Wagner, 1847 (including fosteri Thomas, 1924 ; henseli Thomas, 1888a ; itatiayae Miranda-Ribeiro, 1936 ; lundi Matschie, 1916 ; paulensis Vieira, 1950; and sorex Hensel, 1872 ); and unistriata Wagner, 1842 . DIAGNOSIS: (Asterisks in this section indicate traits exhibited by Monodelphis dimidiata that have yet to be confirmed for M. unistriata .) Dorsal body pelage grayish middorsally, with ( M. unistriata ) or without ( M. dimidiata ) a single dark longitudinal stripe, contrasting with clear yellowish, orange, or reddish flanks; ventral pelage uniformly colored (yellowish, orangish, or reddish), without self-whitish markings. Mammae 6–5–6 = 17 to 11–5–11 = 27 ( Thomas, 1888b: 361 ), including abdominal-inguinal and pectoral teats.* Thenar and first interdigital pads of hind foot separate*; hypothenar pad of hind foot absent.* Body pelage extends onto the tail to about the same extent dorsally and ventrally; tail scales arranged in spiral series. Infraorbital foramen dorsal to P3 or M1; frontal process of jugal present but rounded, not distinctly angular*; parietal usually (> 90% of examined specimens) in contact with mastoid*; incisive foramina short; maxillopalatine fenestrae short; sphenorbital fissure usually large, exposing basisphenoid laterally*; infratemporal crest of alisphenoid distinct*; secondary foramen ovale usually absent (rarely present bilaterally)*; tympanic wing of alisphenoid usually small*; tip of anterior process of the malleus exposed or not on external surface of bulla*; rostral tympanic process of petrosal triangular (not broadly rounded), but sometimes concealing fenestra cochleae ventrally*; 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: Comparisons of Monodelphiops with other subgenera of Monodelphis have already been provided (see above). REMARKS: Molecular sequence data are currently unavailable from Monodelphis unistriata , so inferences about its relationships are necessarily based on morphology. Although Pine et al. (2013) recovered M. unistriata as the sister taxon of M. iheringi based on a combined analysis of morphological characters and cytochrome- b sequences (the latter coded as missing for M. unistriata ), the authors themselves stated that the characters sampled for their study were not “sufficiently informative as to allow refined elucidation of the relationships in this genus” ( Pine et al., 2013: 433 ), and that additional characters as well as inclusion of other species would be necessary to “ever more firmly ascertain the relationships of this enigmatic taxon” ( Pine et al., 2013: 435 ). They also noted multiple morphological similarities between M. unistriata and M. dimidiata , suggesting that M. unistriata could be more closely related to M. dimidiata than to any other species ( Pine et al., 2013: 432 ). Among several possible explanations for such anomalous results, M. unistriata is known from just two specimens, one consisting only of a skin and the other of a skin and part of the skull ( Pine et al., 2013 : fig. 2 ), so information is missing for many morphological characters, including those of the posterior braincase, zygomatic arches, and ear region. We hypothesize that M. unistriata and M. dimidiata are sister taxa based on shared attributes that seem likely to optimize as synapomorphies in future phylogenetic analyses. Such attributes include: a dorsal body pelage with a grizzled middorsum contrasting with clear yellowish, orange, or reddish flanks; large tail scales arranged in spiral series; very short incisive foramina (a striking similarity previously noted by Pine et al., 2013 ); and short maxillopalatine fenestrae. Of course, this hypothesis needs to be tested using taxon-dense phylogenetic analyses of morphological and molecular data when fresh material of this apparently elusive species become available. NOTES ON DISTRIBUTION AND SYMPATRY: Monodelphiops occurs in southeastern Brazil , eastern Paraguay , Uruguay , and northeastern Argentina ( Vilela et al., 2010 ; Pine et al., 2013 ) ( table 3 ), where it is sometimes sympatric with Mygalodelphys and Microdelphys (see previous accounts).