Craniodental Morphology And Phylogeny Of Marsupials Author Beck, Robin M. D. School of Science, Engineering and Environment University of Salford, U. K. & School of Biological, Earth & Environmental Sciences University of New South Wales, Australia & Division of Vertebrate Zoology (Mammalogy) American Museum of Natural History Author Voss, Robert S. Division of Vertebrate Zoology (Mammalogy) American Museum of Natural History Author Jansa, Sharon A. Bell Museum and Department of Ecology, Evolution, and Behavior University of Minnesota text Bulletin of the American Museum of Natural History 2022 2022-06-28 2022 457 1 353 https://bioone.org/journals/bulletin-of-the-american-museum-of-natural-history/volume-457/issue-1/0003-0090.457.1.1/Craniodental-Morphology-and-Phylogeny-of-Marsupials/10.1206/0003-0090.457.1.1.full journal article 10.1206/0003-0090.457.1.1 0003-0090 6971356 † Thylatheridium SPECIES SCORED: † Thylatheridium cristatum ( type species). GEOLOGICAL PROVENANCE OF SCORED SPECIMENS : Barranca de los Lobos Formation and Chapadmalal Formation (including “Playa Estafeta,” “nivel VI-VII,” “Los Acantilados,” and “Las Palomas”), Mar del Plata, Buenos Aires Province , Argentina . AGE OF SCORED SPECIMENS: The Barranca de los Lobos Formation is considered to represent the Barrancalobian substage of the Marplatan stage/age (Cione et al., 2015: fig. 2; Beck and Taglioretti, 2020), which is about 2.9–3.3 Mya (Woodburne, 2010: fig. 3; Prevosti and Forasiepi, 2018: table 1.1 ). As noted above (see † Sparassocynus ), the Chapadmalal Formation is thought to fall within the interval from 3.3 to about 5 Mya. ASSIGNED AGE RANGE : 5.000 –2.900 Mya. REMARKS: Reig (1952) erected the genus † Thylatheridium and described a single species, † T. cristatum , based on a well-preserved skull ( MACN 6442) and additional specimens collected from late Pliocene localities near Chapadmalal, Mar del Plata. Two other species have been named—† T . hudsoni and † T. pascuali (see Reig, 1952; Goin and Montalvo, 1988)—although the latter was described as “dubious” by Forasiepi et al. (2009). † Hesperocynus dolgopolae was also originally described as a species of † Thylatheridium (see † Hesperocynus above). † Thylatheridium has been considered by most authors to be most closely related to the Recent didelphid Monodelphis (Reig, 1952; Reig et al., 1987; Goin and Montalvo, 1988; Goin, 1991, 1995; Goin and Rey, 1997; Goin et al., 2000; Voss and Jansa, 2009). This hypothesis was formalized by Voss and Jansa (2009), who referred † Thylatheridium to the didelphid tribe Marmosini , together with Marmosa , Monodelphis , and Tlacuatzin . Beck and Taglioretti (2020) proposed restricting the name Marmosini to the Marmosa lineage only (or possibly to Marmosa + Tlacuatzin , if these two genera form a clade), and using Monodelphini to refer to the Monodelphis lineage (see also Goin, 1991, 1995; Goin and Rey, 1997; Goin et al., 2000), in which case Thylatheridium may also be a monodelphin. Indeed, it is possible that † Thylatheridium is actually nested within Monodelphis (Reig, 1958: 90; Voss and Jansa, 2009: 101). By contrast, Simpson (1972) argued in favor of a closer relationship between † Thylatheridium and Lestodelphys (a member of the Recent didelphid tribe Thylamyini ), and some of the phylogenetic analyses of Reig et al. (1987: figs. 65, 67) placed † Thylatheridium in a clade with both Lestodelphys and Thylamys , to the exclusion of Monodelphis . Regardless, it seems certain that † Thylatheridium is a member of Didelphidae sensu Voss and Jansa (2009) .