Review of the extinct ‘shrew-opossums’ (Marsupialia: Caenolestidae), with descriptions of two new genera and three new species from the Early Miocene of southern South America

Abstract

We present a systematic review of the extinct species included in the family Caenolestidae, one of the few South American metatherian groups that has survived to the present. We perform a cladistic analysis based on a data matrix consisting of all extant and extinct species that have been referred to this family, 100 morphological characters and two sets of molecular data (cytochrome b and cytochrome c oxidase I). Morphological and molecular data were analysed separately and in combination, under maximum parsimony and maximum likelihood methods. As a result, caenolestids are recovered as a monophyletic group within which we formally recognize three new taxa: Caenolestoides miocaenicus gen. & sp. nov., Gaimanlestes pascuali gen. & sp. nov. and Stilotherium parvum sp. nov. from the Early Miocene of Patagonia, Argentina. Stilotherium is the earliest diverging lineage of caenolestids followed by Gaimanlestes, while C. miocaenicus was recovered as the extinct species most closely related to extant caenolestids.

Craniodental Morphology and Phylogeny of Marsupials

“…Both of our craniodental analyses recover relationships within Paucituberculata that conflict with recent studies of paucituberculatan phylogeny (Abello, 2007;Goin et al, 2007b;Goin et al, 2009a;Abello, 2013;Forasiepi et al, 2013;Rincón et al, 2015;Abello et al, 2018;Abello et al, 2021). In particular, neither of our analyses groups †Evolestes with other paucituberculatans, whereas this important fossil has been consistently recovered as a plesiomorphic paucituberculatan in other published analyses (Goin et al, 2007b;Abello, 2013;Rincón et al, 2015;Abello et al, 2018;Abello et al, 2021).…”

“…For fossil didelphids, the positions of †Thylophorops within Didelphini, and †Thylatheridium and the sparassocynins †Hesperocynus and 297 †Sparassocynus in a clade with Monodelphis are in agreement with previous studies (Reig, 1958b;Goin and Rey, 1997;Voss and Jansa, 2009;Beck and Taglioretti, 2020). Within Paucituberculata, †Evolestes groups with the other paucituberculatan terminals, †Acdestis and †Palaeothentes form a clade (= †Palaeothentidae), and †Stilotherium is sister to crown-clade Caenolestidae, all of which are in closer agreement with other published studies (Abello, 2007;Goin et al, 2007b;Goin et al, 2009a;Abello, 2013;Forasiepi et al, 2013;Rincón et al, 2015;Abello et al, 2018;Abello et al, 2021) than are our craniodental results. However, as in our craniodental analyses (see above), the presence of †Pichipilus within the paucituberculatan crown clade conflicts with several published studies that place †Pichipilus closer to †Palaeothentidae (represented here by †Acdestis and †Palaeothentes) within the superfamily †Palaeothentoidea.…”

“…Both of our craniodental analyses recover relationships within Paucituberculata that conflict with recent studies of paucituberculatan phylogeny (Abello, 2007;Goin et al, 2007b;Goin et al, 2009a;Abello, 2013;Forasiepi et al, 2013;Rincón et al, 2015;Abello et al, 2018;Abello et al, 2021). In particular, neither of our analyses groups †Evolestes with other paucituberculatans, whereas this important fossil has been consistently recovered as a plesiomorphic paucituberculatan in other published analyses (Goin et al, 2007b;Abello, 2013;Rincón et al, 2015;Abello et al, 2018;Abello et al, 2021). Our analyses also conflict with these other recent studies in failing to group the fossil caenolestid †Stilotherium with extant caenolestids, instead placing †Pichipilus (a pichipilid palaeothentoid) within crown-clade Caenolestidae, and in failing to recover monophyly of †Palaeothentoidea (= †Acdestis+ †Palaeothentes+ †Pichipilus) or †Palaeothentidae (= †Acdestis+ †Palaeothentes).…”

“…The grouping of †Pichipilus with extant caenolestids may be due to the shared presence of an anteorbital vacuity, which is absent in †Acdestis and †Palaeothentes (the condition in †Stilotherium is unknown; character 4). In addition, we have included only the best preserved fossil paucituberculatan taxa as terminals here, whereas other studies (Abello, 2007;Goin et al, 2007b;Goin et al, 2009a;Abello, 2013;Forasiepi et al, 2013;Rincón et al, 2015;Abello et al, 2018;Abello et al, 2021) have included a much denser sampling of fossil paucituberculatans (including taxa only known from fragmentary dental remains), and they have used a wider range of paucituberculatan-specific morphological characters that could not be included here due to the difficulty of scoring them consistently across our broader taxonomic sampling.…”

“…32), probably due to the relative incompleteness of relevant fossil material (Goin et al, 2007b;: indeed, †Evolestes is the least complete of all our terminals, being 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; and in subsequent studies that have examined the phylogenetic relationships of Paucituberculata (Abello, 2013;Forasiepi et al, 2013;Rincón et al, 2015;Abello et al, 2018;Abello et al, 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.…”