Diprotodontia Owen, 1866

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 : 226

Diprotodontia Owen, 1866

CONTENTS: Acrobatidae , † Balbaridae , Burramyidae , †Diprotodontoidea, † Ekaltadeta , Hypsiprymnodontidae , † Ilariidae , Macropodidae , † Muramura , † Namilamadeta , Petauridae , Phalangeridae , Phascolarctidae , Potoroidae , Pseudocheiridae , Tarsipedidae , † Thylacoleonidae , and Vombatidae .

STEM AGE: 45.6 Mya (95% HPD: 41.4–48.8 Mya).

CROWN AGE: 39.8 Mya (95% HPD: 35.5–45.2 Mya).

UNAMBIGUOUS CRANIODENTAL SYNAPOMORPHIES: Maxillary foramen contained entirely within the maxilla (char. 14: 0→1; ci = 0.200); glenoid process of alisphenoid absent (char. 23: 1→0; ci = 0.125); sagittal crest small in adults, extending from nuchal crest onto parietals, but not extending onto frontals (char. 27: 0→1; ci = 0.059); pterygoids long, extending posteriorly to sheath the ventral margin of the carotid canal (char. 47: 0→1; ci = 0.333); hypotympanic sinus roof formed by squamosal and petrosal only (char. 54: 0→2; ci = 0.182); posterior squamosal epitympanic sinus distinct and at least partially enclosed laterally (char. 84: 0→1; ci =0.067); zygomatic epitympanic sinus present (char. 85: 0→1; ci = 0.500); P3 semisectorial (char. 123: 0→1; ci = 0.385); P3 erupts before M3 (char. 130: 2→4; ci = 0.089); upper molars without a distinct ectoflexus on any tooth (char. 132: 1→0; ci = 0.333); upper molar posterolingual cusp formed by metaconule (char. 143: 0→1; ci = 0.400); anteriormost lower incisor large, long crowned, and conspicuously procumbent (char. 147: 0→1; ci = 0.500); i2–4 missing (char. 148: 1→3; ci = 0.750); lower canine absent (char. 152: 0→1; ci = 1.000); m1 paracristid unnotched (char. 160: 0→1; ci = 0.125); and hypoconulid absent or indistinct (char. 178: 0→1; ci = 0.333).

COMMENTS: Diprotodontian monophyly is strongly supported in all our molecular (figs. 27–29) and total-evidence (figs. 32, 33) analyses, and a long list craniodental features optimize as unambiguous synapomorphies on our dated total evidence topology ( fig. 33). Importantly, although Diprotodontia (homoplastically) shares with † Yalkaparidon and paucituberculatans an enlarged, gliriform anteriormost lower incisor, it is characterized by numerous other craniodental synapomorphies that are not seen in these other taxa (see Aplin, 1990: 355–375, for a detailed discussion of the diprotodontian “morphotype”). However, we note that several of these traits are subsequently modified or reversed within Diprotodontia .

Our analyses suggest that Diprotodontia diverged from its sister taxon ( Microbiotheria ) during the early or middle Eocene and diversified during the middle or late Eocene; this schedule is distinctly later than that proposed by most previous molecular-clock studies ( Nilsson et al., 2004; Beck, 2008a; Meredith et al., 2008b, 2009a, 2009 c, 2011; Mitchell et al., 2014; Duchêne et al., 2018), but it is similar to the scenario implied by estimated dates in the recent phylogenomic study of Álvarez-Carretero et al. (2021). Regardless of its precise timing, this initial diversification is not preserved in the Australian fossil record due to the long temporal hiatus between the early Eocene Tingamarra Local Fauna (from which diprotodontians have not been identified) and multiple Australian sites known from the late Oligocene, in which definitive diprotodontians (including representatives of many modern diprotodontian families) are known ( Archer et al., 1999; Long et al., 2002; Archer and Hand, 2006; Black et al., 2012b).

As already noted (see Australidelphia above), isolated australidelphian tarsals from the middle Eocene La Barda locality in Argentina were placed within Diprotodontia in the morphological phylogenetic analysis of Lorente et al. (2016). However, the relationships supported within Diprotodontia in that analysis are strongly incongruent with the analyses presented here, as well as with the results of other recent molecular studies (e.g., Nilsson et al., 2004; Beck, 2008a; Meredith et al., 2008b, 2009 c, 2011; Mitchell et al., 2014; May-Collado et al., 2015; Duchêne et al., 2018; Álvarez-Carretero et al., 2021); furthermore, dental remains of definitive (crownclade) diprotodontians have not been described from La Barda or any other fossil locality outside Australia and New Guinea ( Goin et al., 2016). Thus, the identity of the La Barda tarsals as diprotodontian (rather than another australidelphian lineage) should be treated as questionable based on available evidence. Instead, the oldest definitive diprotodontians are from the late Oligocene of Australia ( Archer et al., 1999; Long et al., 2002; Archer and Hand, 2006; Black et al., 2012b).