96 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322 Fig. 39. Caluromysiops irrupta (a composite illustration based on several imperfect adult specimens, mostly from zoos: AMNH 208101, 244364; USNM 397626; FMNH 84426).
2009 VOSS AND JANSA: DIDELPHID MARSUPIALS 97 posterior cutting edges. Upper canine (C1) alveolus contained entirely within maxillary bone; C1 simple (without accessory cusps), <strong>and</strong> very large in adult specimens. First upper premolar (P1) absent or minute <strong>and</strong> vestigial; second upper premolar (P2) much taller than P3; P3 with both anterior <strong>and</strong> posterior cutting edges; upper milk premolar (dP3) large <strong>and</strong> molariform. Molars not carnassialized (postmetacristae subequal to postprotocristae); relative widths M1 , M2 . M3 . M4; centrocrista straight (uninflected) on M1–M3; ect<strong>of</strong>lexus absent on all upper molars; anterolabial cingulum continuous with preprotocrista (complete anterior cingulum present) on M3; postprotocrista without carnassial notch. Last upper tooth to erupt is P3. Lower incisors (i1–i4) with distinct lingual cusps. Lower canine (c1) erect, acutely pointed, <strong>and</strong> simple (without a posterior accessory cusp). Second lower premolar (p2) much taller than p3; lower milk premolar (dp3) large <strong>and</strong> nonvestigial, but paraconid not well developed (trigonid incomplete). Hypoconid labially salient on m3; hypoconulid not twinned with entoconid on any lower molar; entoconid much taller than hypoconulid on m1–m3. DISTRIBUTION: Caluromysiops is currently known from just seven localities in the rainforested Amazonian lowl<strong>and</strong>s <strong>of</strong> southeastern Colombia, eastern Peru <strong>and</strong> western Brazil (Emmons, 2008). REMARKS: Various authors (e.g., Cabrera, 1958; Simpson, 1972; Izor <strong>and</strong> Pine, 1987) have questioned whether it is useful to separate Caluromysiops from Caluromys, but none explicitly considered the suite <strong>of</strong> trenchant morphological characters that distinguish these taxa. Among other features, Caluromysiops differs from Caluromys by its lack <strong>of</strong> a circumocular mask <strong>and</strong> dark midrostral stripe, presence <strong>of</strong> dark scapular stripes, shorter tail (table 5), absence <strong>of</strong> a premaxillary rostral process, co-ossified frontals, presence <strong>of</strong> a well-developed sagittal crest, presence <strong>of</strong> a secondary foramen ovale, globular (versus conical) alisphenoid bullae, columelliform stapes, linear centrocrista, <strong>and</strong> untwinned hypoconulid. Although there is no cladistic problem with combining these taxa under a single generic name, maintaining current binomial usage is likewise unobjectionable <strong>and</strong> serves to separate the monophyletic cluster <strong>of</strong> species currently known as Caluromys from its long-branched sister taxon. Subfamily Hyladelphinae, new CONTENTS: Hyladelphys. DIAGNOSIS: Members <strong>of</strong> this clade uniquely differ from other <strong>didelphid</strong>s 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 <strong>and</strong> members <strong>of</strong> other <strong>didelphid</strong> subfamilies were tabulated by Jansa <strong>and</strong> Voss (2005: table 2). REMARKS: Given the <strong>phylogenetic</strong> results at h<strong>and</strong>, 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 <strong>of</strong> rank is not biologically meaningful, the former option serves to emphasize the intermediate position <strong>of</strong> this odd little opossum between basal <strong>didelphid</strong>s (Glironia <strong>and</strong> caluromyines) <strong>and</strong> the speciose radiation <strong>of</strong> lineages that are more closely related to Didelphis. The branch leading to Hyladelphys is very long in most molecular reconstructions <strong>of</strong> <strong>didelphid</strong> anagenesis (e.g., fig. 33), suggesting an ancient history <strong>of</strong> independent evolution accompanied by extinction <strong>of</strong> transitional forms; the same conclusion is suggested by its uniquely reduced milk dentition <strong>and</strong> by characters <strong>of</strong> the postcranial skeleton (Flores, 2009). In effect, excluding Hyladelphys from Didelphinae simplifies the diagnosis <strong>of</strong> the latter clade <strong>and</strong> provides a new higher taxon to accommodate fossil relatives <strong>of</strong> the former, should any be discovered. Hyladelphys Voss et al., 2001 Figure 40 CONTENTS: kalinowskii Hershkovitz, 1992. MORPHOLOGICAL DESCRIPTION: Combined adult length <strong>of</strong> head <strong>and</strong> body ca. 75–95 mm; adult weight ca. 10–20 g. Rhinarium with two ventrolateral grooves on each side <strong>of</strong> median sulcus; dark circumocular mask
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