A nearly complete juvenile skull of the marsupial Sparassocynus derivatus from the Pliocene of Argentina, the affinities of “sparassocynids”, and the diversification of opossums (Marsupialia; Didelphimorphia; Didelphidae)

Beck, RMD; Taglioretti, ML

Abstract

“Sparassocynids” are small, carnivorously-adapted marsupials known from the late
Miocene and Pliocene of South America, thought to be relatives of living didelphid
opossums but of otherwise uncertain phylogenetic relationships. Here, we describe a
nearly complete juvenile skull of the “sparassocynid” Sparassocynus derivatus, from the Pliocene (~5-3 million years old) Chapadmalal Formation, Argentina. It provides new information on the morphology of Sparassocynus, including the deciduous dentition, and (together with previously collected specimens) allows reinterpretation of the derived auditory region of “sparassocynids.” The new specimen also exhibits several distinctive apomorphies characteristic of Didelphidae and of subclades within the family. Undated Bayesian phylogenetic analysis of a total evidence dataset (132 craniodental characters, 7.3 kb of DNA sequence data from five nuclear genes) places “sparassocynids” within the didelphid genus Monodelphis, whereas “tip-andnode” dating analysis of the same dataset with an Independent Gamma Rates (IGR) clock model places them as sister to Monodelphis, showing that temporal information influenced the resultant topology. We conclude that “sparassocynids” warrant tribal separation only, as Sparassocynini new rank. Based on our dated phylogeny, we also provide a revised scenario for didelphid diversification. Crown-clade didelphids probably originated close to the Oligocene-Miocene boundary. We agree with previous proposals that the appearance of carnivorously-adapted didelphids in South America during the late Miocene, including sparassocynins, is likely related to a decline in diversity of the sparassodonts at this time, and that the disappearance of these carnivorously-adapted didelphids at the end of the Pliocene may have been due to the arrival of placental carnivorans, such as mustelids, from North America.

Citation

Beck, R., & Taglioretti, M. (2020). A nearly complete juvenile skull of the marsupial Sparassocynus derivatus from the Pliocene of Argentina, the affinities of “sparassocynids”, and the diversification of opossums (Marsupialia; Didelphimorphia; Didelphidae). Journal of Mammalian Evolution, 27, 385-417. https://doi.org/10.1007/s10914-019-09471-y

• Journal Article Type: Article
• Acceptance Date: Jun 4, 2019
• Online Publication Date: Jul 23, 2019
• Publication Date: Sep 1, 2020
• Deposit Date: Jun 5, 2019
• Publicly Available Date: Aug 8, 2019
• Journal: Journal of Mammalian Evolution
• Print ISSN: 1064-7554
• Electronic ISSN: 1573-7055
• Publisher: Springer Verlag
• Volume: 27
• Pages: 385-417
• DOI: https://doi.org/10.1007/s10914-019-09471-y
• Publisher URL: https://link.springer.com/article/10.1007/s10914-019-09471-y
• Related Public URLs: https://link.springer.com/journal/10914
• Additional Information: Funders : National Science Foundation;Australian Research Council;Santander Travel Award; Grant Number: DEB-0743039; Grant Number: DE120100957