4 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322 References...................................................... . 142 Appendix1:MorphologicalSpecimensExamined........................... 157 Appendix2:SpecimensSequencedforNuclearGenes........................ 160 Appendix 3: Nonmolecular Character Descriptions .......................... 161 Appendix4:NonmolecularDataMatrix ................................ . 170 Appendix5:NonmolecularApomorphyList ............................. . 171 Appendix6:KeytotheDidelphidGenera............................... . 174
ABSTRACT This report summarizes a decade <strong>of</strong> morphological <strong>and</strong> molecular research on the <strong>phylogenetic</strong> <strong>relationships</strong> <strong>of</strong> <strong>didelphid</strong> <strong>marsupials</strong> (opossums), a substantially intact radiation <strong>of</strong> New World metatherian mammals. We review the comparative morphology <strong>of</strong> Recent opossums, emphasizing those anatomical systems from which taxonomically useful information is available for the majority <strong>of</strong> living genera <strong>and</strong> species, namely the integument, cranium, <strong>and</strong> dentition. Morphological similarities <strong>and</strong> differences among <strong>didelphid</strong>s <strong>and</strong> other plesiomorphic <strong>marsupials</strong> (caenolestids, microbiotheriids, dasyurids, <strong>and</strong> peramelids) are also described. These observations, representing evolved differences in diverse functional-morphological systems, together with karyotypic information gleaned from the literature, provide the basis for coding 129 <strong>phylogenetic</strong> characters that we scored for 44 ingroup <strong>and</strong> seven outgroup taxa. Published information about the size, internal organization, chromosomal location, <strong>and</strong> physiological properties <strong>of</strong> five nuclear genes (BRCA1, DMP1, IRBP, RAG1, vWF) sequenced for this study suggest that these loci are unlinked, exist as single copies, are active in different tissues, <strong>and</strong> encode protein products with widely divergent functions. All <strong>of</strong> the sequenced fragments are long (.900 bp), free <strong>of</strong> ingroup alignment ambiguities, <strong>and</strong> translate to open reading frame. Nucleotide data from a total <strong>of</strong> 7320 aligned sites were obtained from 43 ingroup <strong>and</strong> seven outgroup taxa. Separate parsimony, likelihood, <strong>and</strong> Bayesian analyses <strong>of</strong> these six data partitions (morphology + karyotypes, five genes) resulted in highly congruent estimates <strong>of</strong> <strong>didelphid</strong> phylogeny with few examples <strong>of</strong> conflict among strongly supported nodes. Analyses <strong>of</strong> concatenated sequences <strong>and</strong> combined (nonmolecular + sequence) datasets effectively summarize all <strong>of</strong> the common signal recovered from separate analyses: a completely resolved ingroup phylogeny with high support statistics at most nodes. Remaining problems (not conclusively resolved in this study) include the position <strong>of</strong> the ingroup root <strong>and</strong> the <strong>relationships</strong> <strong>of</strong> three genera (Chacodelphys, Cryptonanus, Tlacuatzin) within their respective suprageneric clades. The history <strong>of</strong> <strong>didelphid</strong> <strong>classification</strong> is reviewed, <strong>and</strong> all previous systems are found to contain nonmonophyletic groups. A revised <strong>phylogenetic</strong> <strong>classification</strong> consistent with our analytic results includes the following higher taxa: Glironiinae (for Glironia), Caluromyinae (Caluromys <strong>and</strong> Caluromysiops), Hyladelphinae (Hyladelphys), Didelphinae (Marmosini, Metachirini, Didelphini, <strong>and</strong> Thylamyini), Marmosini (Marmosa, Monodelphis, <strong>and</strong>Tlacuatzin), Metachirini (Metachirus), Didelphini (Chironectes, Didelphis, Lutreolina, <strong>and</strong>Phil<strong>and</strong>er), <strong>and</strong> Thylamyini (Chacodelphys, Cryptonanus, Gracilinanus, Lestodelphys, Marmosops, <strong>and</strong>Thylamys). The probable <strong>relationships</strong> <strong>of</strong> several Neogene fossil genera are also discussed. To facilitate identifications, all Recent genera are redescribed, representative crania are illustrated, <strong>and</strong> a key is provided. INTRODUCTION They affirme that there are trees <strong>of</strong> suche byggenes, that xvi men ioyninge h<strong>and</strong>es togyther <strong>and</strong> st<strong>and</strong>inge in coompasse, can scarsely embrase sum <strong>of</strong> them. Emonge these trees is fownde that monstrous beaste with a snowte lyke a foxe, a tayle lyke a marmasette, eares lyke a batte, h<strong>and</strong>es lyke a man, <strong>and</strong> feete lyke an ape, bearing her whelpes abowte with her in an owtwarde bellye much lyke vnto a greate bagge or purse. — Richard Eden (1555), describing the first European encounter with a marsupial, by Vicente Yáñez Pinzón <strong>and</strong> his men on the coast <strong>of</strong> Brazil in the year 1500 The oldest known metatherian mammals occur in Cretaceous sediments <strong>of</strong> eastern 5 Asia <strong>and</strong> western North America (Rougier et al., 1998; Luo et al., 2003; Kielan-Jaworowska et al., 2004), <strong>and</strong> other early metatherians are present in the Tertiary record <strong>of</strong> Europe <strong>and</strong> Africa (Crochet, 1980; Kurz, 2007; Hooker et al., 2008). The metatherian crown group Marsupialia, however, probably evolved in South America <strong>and</strong> subsequently dispersed across Antarctica to Australia <strong>and</strong> New Guinea (Muizon et al., 1997; Springer et al., 1997a; Rougier et al., 1998). Living <strong>marsupials</strong> comprise seven major groups, currently ranked as orders in the Linnaean hierarchy, each <strong>of</strong> which is endemic to either the New World or the Old World (table 1). Although the extant New World marsupial fauna consists <strong>of</strong> three orders, two <strong>of</strong> these
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