Paucituberculata Ameghino, 1894

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 : 202-203

Paucituberculata Ameghino, 1894

CONTENTS: Caenolestidae , † Evolestes , † Palaeothentidae , † Pichipilus , and † Stilotherium .

STEM AGE: 39.9 Mya (95% HPD: 30.7–49.7 Mya).

CROWN AGE: 35.0 Mya (95% HPD: 28.2–44.2 Mya).

UNAMBIGUOUS CRANIODENTAL SYNAPOMORPHIES: None (but see Comments, below).

COMMENTS: † Evolestes was not recovered as a member of Paucituberculata in our craniodental analyses (figs. 30, 31) nor in our undated totalevidence analysis (fig. 32), probably due to the relative incompleteness of relevant fossil material ( Goin et al., 2007b, 2010): indeed, † Evolestes is the least complete of all our terminals, scoreable for only 53 out of the 180 characters (rendering it 29.4% complete; table 4 ). However, the original descriptions of † Evolestes specimens by Goin et al. (2007b, 2010) and in subsequent studies that have examined the phylogenetic relationships of Paucituberculata ( Abello, 2013; Forasiepi et al., 2013; Rincón et al., 2015; Engelman et al., 2016; Abello et al., 2020, 2021) collectively present compelling evidence that † Evolestes is indeed a paucituberculatan, albeit a dentally plesiomorphic one. For this reason and to enable us to calibrate the age of the Paucituberculata node, we constrained monophyly of Paucituberculata including † Evolestes for our dated total-evidence analysis ( fig. 33).

However, no craniodental features optimize as an unambiguous synapomorphy for this constrained clade in our dated total-evidence analysis. This is probably due to the incompleteness of † Evolestes already mentioned above and to the fact that the immediate sister taxon of Paucituberculata in this analysis is † Yalkaparidon . The latter result has two unfortunate consequences: first, some features that might otherwise optimize as paucituberculatan synapomorphies (e.g., a gliriform anteriormost lower incisor) are instead optimized as synapomorphies of Paucituberculata + † Yalkaparidon (see file S 3 in the online supplement); and second, other traits optimize ambiguously because they are inapplicable in † Yalkaparidon . Neverthless, three traits that optimize as paucituberculatan synapomorphies under Accelerated Transformation—subadult fusion of median parietal suture (char. 25: 0→1; ci = 0.143), presence of a large retrodental canal (char. 100: 0→1; ci = 1.000), and m1 paracristid unnotched (char. 160; ci = 0.125)—represent distinctive features that are undoubtedly absent in † Yalkaparidon . A further three traits that optimize as paucituberculatan synapomorphies under Delayed Transformation—centrocrista discontinuous, with postparacrista and premetacrista terminating in stylar region (char. 140: 2→5; ci = 0.333), upper molar posterolingual cusp formed by metaconule (char. 143: 0→1; ci = 0.400), and paracristids of m2 and m3 deflected posterolingually by hypoconulid of preceding tooth (char. 162: 1→0; ci = 1.000)—are inapplicable in † Yalkaparidon .

The relationships within Paucituberculata supported in our dated total-evidence analysis show some differences from those of published phylogenetic analyses of paucituberculatans ( Goin et al., 2007b; 2009a; Abello, 2013; Forasiepi et al., 2013; Rincón et al., 2015; Engelman et al., 2016; Abello et al., 2020, 2021). Most notably, † Pichipilus (currently classified as a pichipilid palaeothentoid) does not form a clade with the palaeothentids † Acdestis and † Palaeothentes as found in other studies, but instead is placed closer to living caenolestids than is the caenolestid † Stilotherium . This may be due to the shared presence of an anteorbital vacuity in † Pichipilus and extant caenolestids, whereas this structure is definitively absent in † Acdestis and † Palaeothentes and the condition in † Stilotherium is unknown (see char. 4). More generally, these discrepancies could be related to our decision to only include paucituberculatans known from relatively complete craniodental material, and because we did not include many paucituberculatan-specific morphological characters (particularly dental characters) that could not be scored consistently across our broader taxonomic sampling.

Although not included in our analyses, the oldest paucituberculatan described to date is probably † Bardalestes hunco from the middle Eocene La Barda locality of Argentina ( Goin et al., 2009a). † Riolestes draco , from the slightly older ( Woodburne et al., 2014a) Itaboraí Local Fauna of Brazil, may be based on a deciduous lower premolar ( Goin et al., 2009a; R.M.D.B., personal obs.), and is not unequivocally paucituberculatan. Our estimate for the age of the divergence between † Evolestes and our other paucituberculatatan terminals spans a broad range when the 95% HPD is taken into account, from the middle Eocene to the middle Oligocene. However, this is still younger than the ~48 Mya estimate for this split presented by Abello et al. (2020: fig. 2), which was based on a posteriori timescaling of a strict consensus of most-parsimonious trees rather than a phylogenetic analysis with a clock model.