Phalangeroidea Thomas, 1888

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 : 237-239

Phalangeroidea Thomas, 1888

CONTENTS: Ailurops , † Onirocuscus , Phalanger (fig. 47), Spilocuscus , Strigocuscus , Trichosurus , “ Trichosurus ” † dicksoni , and Wyulda .

STEM AGE: 29.9 Mya (95% HPD: 25.8–35.4 Mya).

CROWN AGE: 18.4 Mya (95% HPD: 14.1–23.7 Mya).

UNAMBIGUOUS CRANIODENTAL SYNAPOMORPHIES: One lacrimal foramen usually present (char. 10: 0→1; ci = 0.063); squamosal and pars canalicularis of the petrosal extensively pneumatized and cancellous (char. 87: 0→1; ci = 0.250); mastoid exposure of petrosal restricted to ventralmost part of occiput, not contacting supraoccipital (char. 90: 0→1; ci = 1.000); major crest of semi- or fully sectorial P3 oriented posterolingual to anterolabial (char. 127: 1→0; ci = 0.400); cristid obliqua with strongly developed buccal kink (char. 168: 0→1; ci = 0.333); and entocristid with distinct anterolabial kink (char. 177: 0→2; ci = 0.250).

COMMENTS: Monophyly of the only phalangeroid family included here, namely Phalangeridae , is strongly supported by a number of distinctive craniodental apomorphies, several of which show relatively low homoplasy. Relationships among modern phalangerids in our molecular (figs. 27–29) and total-evidence (figs. 32, 33) analyses are congruent with the results of recent molecular studies ( Ruedas and Morales, 2005; Raterman et al., 2006; Phillips and Pratt, 2008; Meredith et al., 2009a; Mitchell et al., 2014; May-Collado et al., 2015; Duchêne et al., 2018; Álvarez-Carretero et al., 2021; see also Jackson and Groves, 2015; Eldridge et al., 2019) in supporting a split between Trichosurus + Wyulda (= Trichosurinae) and the remaining modern genera. Within Phalangerinae, there is support for Ailurops + Strigocuscus (=Ailuropinae) and Phalanger + Spilocuscus (= Phalangerinae), again in agreement with recent molecular studies ( Ruedas and Morales, 2005; Raterman et al., 2006; Meredith et al., 2009a; Mitchell et al., 2014; May-Collado et al., 2015; ÁlvarezCarretero et al., 2021; see also Jackson and Groves, 2015; Eldridge et al., 2019).

The relationships of the two fossil phalangerids included here, “ Trichosurus ” † dicksoni and † Onirocuscus reidi , differ markedly between the undated and dated total-evidence analyses. In the undated analysis (fig. 32), “ Trichosurus ” † dicksoni forms a clade with Wyulda , with the modern Trichosurus sister to this clade (suggesting that “ T. ” † dicksoni is a trichosurine), whereas † Onirocuscus is sister to Strigocuscus within Ailuropinae; the latter result is notably similar to the relationship originally inferred by Flannery and Archer ( Flannery and Archer, 1987a), who placed the species currently known as † O. reidi within Strigocuscus . By contrast, in the dated analysis ( fig. 33), both fossil taxa are placed outside crown-clade Phalangeridae , with † Onirocuscus the first to diverge, reflecting the impact that incorporating temporal information can have on tree topology (see also Lee and Yates, 2018; Beck and Taglioretti, 2020; King and Beck, 2020). Crosby’s (2007: fig. 7) informal phylogeny also suggests that “ T. ” † dicksoni and † Onirocuscus are not closely related to the living trichosurines ( Trichosurus and Wyulda ) and Strigocuscus respectively, but it is otherwise incongruent with our molecular and total-evidence results and with other recent molecular studies ( Ruedas and Morales, 2005; Raterman et al., 2006; Meredith et al., 2009a; Mitchell et al., 2014; May-Collado et al., 2015; Álvarez-Carretero et al., 2021). With “ T. ” † dicksoni and † Onirocuscus excluded, our dated total-evidence analysis suggests that the phalangerid crown clade is comparatively young, dating to the middle-tolate Miocene (median estimate: 11.0 Mya; 95% HPD: 8.0–13.1 Mya).

The oldest known fossil phalangerid is † Eocuscus sarastamppi , from the late Oligocene Ditjimanka Local Fauna of the Etadunna Fomation in South Australia ( Case et al., 2008). This interesting taxon is known from a single right maxilla, and so has not been included in our analyses, but it exhibits a number of dental features that are likely plesiomorphic relative to other phalangerids. These include the morphology of its P3, which has its major cutting crest parallel to the upper molars rather than oriented posterolingual to anterolabially as in most other known phalangerids (see char. 127); additionally, this crest lacks obvious enamel ridges (see char. 126), suggesting that the presence of these ridges (as seen in most phalangerids, Burramys , and many macropodiforms) may have arisen multiple times within Phalangerida . Lastly, the protoloph and metaloph of M2 each have a centrally placed cusp in † E. sarastamppi ; although these central cusps were identified as neomorphs by Case et al. (2008), we consider them homologs of the paracone and metacone for reasons previously discussed at length (see char. 136).