Marsupialia, Illiger 1811

Beck, Robin M. D., Voss, Robert S. & Jansa, Sharon A., 2022, Craniodental Morphology And Phylogeny Of Marsupials, Bulletin of the American Museum of Natural History 2022 (457), pp. 1-353 : 197-198

Marsupialia, Illiger 1811

CONTENTS: Dasyuromorphia , Didelphimorphia , Diprotodontia , Microbiotheria , Notoryctemorphia , Paucituberculata , Peramelemorphia , and †Yalkaparidontia.

STEM AGE: 59.7 Mya (95% HPD: 55.6–65.8 Mya).

CROWN AGE: 56.2 Mya (95% HPD: 54.7–58.6 Mya).

UNAMBIGUOUS CRANIODENTAL SYNAPOMORPHIES: Lower molars without a posterior cingulid (char. 180: 1→0; ci = 0.333).

COMMENTS: As noted in our introduction, most recent authors restrict Marsupialia to the metatherian crown clade, and we follow the node-based definition of Marsupialia proposed by Beck et al. (2014: 131): the least inclusive clade containing Didelphis marsupialis , Caenolestes fuliginosus , and Phalanger orientalis . By contrast, † Pucadelphys , † Mayulestes , and † Allqokirus have consistently fallen outside Marsupialia in most published analyses ( Rougier et al., 1998, 2004, 2015; Luo et al., 2003, 2011; Ladevèze and Muizon, 2007; SánchezVillagra et al., 2007; Beck et al., 2008a; Horovitz et al., 2008, 2009; Forasiepi, 2009; Ladevèze and Muizon, 2010; Beck, 2012, 2017a; Williamson et al., 2012, 2014; Engelman and Croft, 2014; Forasiepi et al., 2014a; Wilson et al., 2016; Carneiro and Oliveira, 2017a, 2017b; Maga and Beck, 2017; Bi et al., 2018; Carneiro, 2018, 2019; Carneiro et al., 2018; Muizon et al., 2018; Rangel et al., 2019; Ladevèze et al., 2020; Muizon and Ladevèze, 2020. Notable exceptions to this widespread consensus ( Goin et al., 2006; Velazco et al., 2022) are discussed in the account for † Pucadelphys in appendix 1).

† Mimoperadectes also falls outside Marsupialia in all our craniodental (figs. 30, 31) and total-evidence (figs. 32, 33) analyses. This result conflicts with Horovitz et al. (2009), who recovered † Mimoperadectes as a stem didelphimorphian, but it agrees with most subsequent studies ( Forasiepi, 2009; Beck, 2012; Beck et al., 2014; Engelman and Croft, 2014; Forasiepi et al., 2014a; Suarez et al., 2015; Carneiro, 2018, 2019; Carneiro et al., 2018; Muizon et al., 2018; Rangel et al., 2019; Engelman et al., 2020; Ladevèze et al., 2020; Muizon and Ladevèze, 2020), which have consistently found that † Mimoperadectes and other alleged peradectids are outside the metatherian crown clade. 29 In particular, as we discussed above (see char. 55), † Mimoperadectes appears to lack any kind of tympanic process or bulla enclosing the hypotympanic sinus ventrally, as do our outgroup terminals † Pucadelphys , † Mayulestes , and † Allqokirus , plus several other nonmarsupial metatherians not included here ( Muizon, 1999; Forasiepi, 2009; Bi et al., 2015; Beck, 2017a; Muizon et al., 2018; Muizon and Ladevèze, 2020). However, the polarity of this feature is debated, and there is clear evidence of homoplasy within Metatheria (KielanJaworowska and Nessov, 1990: 7; Forasiepi, 2009: char. 50; Wilson et al., 2016: supplementary information; Beck, 2017a: 402; Muizon et al., 2018; Muizon and Ladevèze, 2020: 683–684).

Our craniodental and undated total-evidence analyses (figs. 30–32) place † Herpetotherium in an unresolved polytomy with Recent marsupials. In contrast to our outgroup terminals and † Mimoperadectes , † Herpetotherium has an ossified hypotympanic sinus floor, which optimizes as an unambiguous synapomorphy of † Herpetotherium + Marsupialia in our results (see supplementary file S 3 in the online supplement: https:// doi.org/10.5531/sd.sp.54). However, most recent published phylogenetic analyses place † Herpetotherium outside Marsupialia ( Ladevèze and Muizon, 2007; Sánchez-Villagra et al., 2007; Beck et al., 2008a; Horovitz et al., 2008, 2009; Forasiepi, 2009; Ladevèze and Muizon, 2010; Beck, 2012; Williamson et al., 2012, 2014; Engelman and Croft, 2014; Forasiepi et al., 2014a; Beck, 2017a; Carneiro and Oliveira, 2017a, 2017b; Maga and Beck, 2017; Carneiro, 2018, 2019; Carneiro et al., 2018; Muizon et al., 2018; Rangel et al., 2019; Muizon and Ladevèze, 2020). Based on these studies, and to enable us to calibrate the age of Marsupialia , we constrained † Herpetotherium to fall outside the crown clade in our dated totalevidence analysis.

With † Herpetotherium constrained to fall outside Marsupialia , only loss of the posterior cingulid optimizes as an unambiguous synapomorphy for the crown clade. Although presence or absence of a posterior cingulid might be a useful criterion for distinguishing marsupials from nonmarsupial marsupialiforms ( Voss and Jansa, 2009: 87), this structure was subsequently reacquired by dasyuromorphians (see below) and by the balbarid macropodiform † Balbaroo (and other balbarids not included here; see Cooke, 1997a: fig. 7, who referred to the posterior cingulid as the “hypocingulid”). Three fossil Australian taxa that have not been included here due to their incompleteness—† Djarthia murgonensis from the early Eocene Tingamarra fauna in northeastern Australia and its probable relatives † Ankotarinja tirarensis and † Keeuna woodburnei from the late Oligocene Etadunna Formation of central Australia —also have a posterior cingulid and appear to comprise a clade of stem australidelphians ( Archer, 1976d; Godthelp et al., 1999; Beck et al., 2008a; Kealy and Beck, 2017), in which case they represent another lineage that independently reacquired this trait. As noted earlier, more or less distinct posterior cingulids have recently been reported in a few extant didelphids ( Voss et al., 2018; Voss et al., 2020), thus revealing additional homoplasy.

As already noted (see above and table 6), our late Palaeocene–early Eocene estimate for the age of the most recent common ancestor of Marsupialia is markedly younger than the estimates proposed in several recent molecular clock analyses ( Meredith et al., 2009 a, 2011; Mitchell et al., 2014; Duchêne et al., 2018) as well as the few other dated total-evidence analyses that have been published to date ( Beck et al., 2016; Maga and Beck, 2017). However, it is more congruent with the recent phylogenomic study of ÁlvarezCarretero et al. (2021).