An ‘ameridelphian’ marsupial from the early Eocene of Australia supports a complex model of Southern Hemisphere marsupial biogeography

Abstract

Recent molecular data strongly support the monophyly of all extant Australian and New Guinean marsupials (Eomarsupialia) to the exclusion of extant South American marsupials. This, together with available geological and fossil evidence, has been used to argue that the presence of marsupials in Australia is simply the result of a single dispersal event from South America during the latest Cretaceous or Palaeocene, without subsequent dispersals between the two continents. Here, I describe an isolated ankle bone (calcaneus) of a metatherian from the early Eocene Tingamarra Local Fauna in northeastern Australia. Strikingly, this specimen, QM F30060, lacks the 'continuous lower ankle joint pattern' (CLAJP), presence of which is a highly distinctive apomorphy of the marsupial clade Australidelphia, which includes Eomarsupialia, the living South American microbiotherian Dromiciops and the Tingamarran fossil marsupial Djarthia. Comparisons with a range of marsupials and stem-metatherians strongly suggest that the absence of the CLAJP in QM F30060 is plesiomorphic, and that this specimen represents the first unequivocal non-australidelphian ('ameridelphian') metatherian known from Australia. This interpretation is confirmed by phylogenetic analyses that place QM F30060 within (crown-group) Marsupialia, but outside Australidelphia. Based on these results, the distribution of marsupials within Gondwana cannot be explained by simply a single dispersal event from South America and Australia. Either there were multiple dispersals by marsupials (and possibly also stem-metatherians) between South America and Australia, in one or both directions, or, alternatively, there was a broadly similar metatherian fauna stretching across southern South America, Antarctica and Australia during the Late Cretaceous-early Palaeogene.

A new species of small-bodied sparassodont (Mammalia, Metatheria) from the middle Miocene locality of Quebrada Honda, Bolivia

“…This arrangement is similar to the results obtained in other phylogenetic studies of marsupials, such as Horovitz and Sánchez-Villagra (2003), Sánchez-Villagra et al (2007), Horovitz et al (2009), andBeck (2012). However, in this study Mayulestes was recovered within the Pucadelphidae rather than as the sister taxon to this group.…”

“…However, Herpetotherium was recovered within crown-group Marsupialia, basal to the Australidelphia, rather than as a sister taxon to the group. This contrasts with the results of several other studies of marsupial phylogenetics (Sánchez-Villagra et al, 2007;Horovitz et al, 2009), but agrees with that of Beck (2012). In contrast to Horovitz et al (2009), we did not recover a close association between the Peradectidae and the Didelphoidea.…”

Post-Gondwana Africa and the vertebrate history of the Angolan Atlantic Coast

“…Eocene mekosuchine crocodylians are also known from localities in Queensland. These faunas reflect, albeit in a depauperate way, the fauna of Austro-Antarctic Gondwana, from which the endemic fauna of Australia was derived (Beck, 2012;Beck et al, 2008;Buchanan, 2009).…”

A new species of Gaylordia Paula Couto (Mammalia, Metatheria) from Itaboraí, Brazil

“…In order to determine the position of Gaylordia within the Metatheria, we performed a maximum parsimony analysis based on the morphological matrix of Beck (2012) and Beck et al (2014). This morphological matrix has been modifi ed from previous studies (Horovitz & Sánchez-Villagra 2003;Sánchez-Villagra et al 2007;Beck et al 2008b;Horovitz et al 2008Horovitz et al , 2009Abello & Candela 2010;Beck, 2012).…”

“…This aspect is of particular importance taking in account that recent phylogenetic studies involving some Paleogene taxa (e.g. Herpetotherium Cope, 1873 andPeradectes Matthew &Granger, 1921, previously referred to the Didelphidae and Peradectidae, respectively), supported their exclusion from the crown-group Marsupialia (Sánchez-Villagra et al, 2007;Beck, 2012;Beck et al, 2014;Engelman & Croft, 2014, but see Horovitz et al, 2009). In this context, the closer relationship of several Itaboraí metatherians with respect to crown-group Marsupialia, especially to "Didelphimorphia", has been a topic of discussion (Goin, 2003;Forasiepi & Rougier, 2009;Ladevèze & Muizon, 2010;Oliveira & Goin, 2011).…”