Hyladelphinae, Voss & Jansa, 2009

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 : 97

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Subfamily Hyladelphinae   , new

CONTENTS: Hyladelphys   .

DIAGNOSIS: Members of this clade uniquely differ from other didelphids by their vestigial milk dentition (dP3/dp3 are large, more or less molariform teeth in other opossums; Voss et al., 2001: table 5). Additional contrasts among hyladelphines and members of other didelphid subfamilies were tabulated by Jansa and Voss (2005: table 2).

REMARKS: Given the phylogenetic results at hand, a monotypic suprageneric taxon for Hyladelphys   could either be ranked as a subfamily (as it is here) or as a tribe (if the genus were referred to the Didelphinae   ). Although the issue of rank is not biologically meaningful, the former option serves to emphasize the intermediate position of this odd little opossum between basal didelphids ( Glironia   and caluromyines) and the speciose radiation of lineages that are more closely related to Didelphis   . The branch leading to Hyladelphys   is very long in most molecular reconstructions of didelphid anagenesis (e.g., fig. 33), suggesting an ancient history of independent evolution accompanied by extinction of transitional forms; the same conclusion is suggested by its uniquely reduced milk dentition and by characters of the postcranial skeleton ( Flores, 2009). In effect, excluding Hyladelphys   from Didelphinae   simplifies the diagnosis of the latter clade and provides a new higher taxon to accommodate fossil relatives of the former, should any be discovered.