Osteology of Arctodictis sinclairi (Mammalia, Metatheria, Sparassodonta) and

FORASIEPI, A.M.

Monografias del Museo Argentino de Ciencias Naturales

Museo Argentino de Ciencias Naturales

Lugar: Buenos Aires; Año: 2009 vol. 6 p. 1 - 174

1515-7652

The anatomy of Arctodictis sinclairi (Sparassodonta, Borhyaenidae) is studied in detail in this work and constitutes the core of the present contribution. The specimen MLP 85-VII-3-1 of Arctodictis sinclairi consists of a nearly complete skeleton exquisitely preserved, collected from Gran Barranca (Chubut Province, Argentina), in outcrops of the Sarmiento Formation (Colhuehuapian SALMA; early Miocene). The detailed description provided new information about the morphology of sparassodonts, which, in turn, served as material basis for comparisons with more distant metatherians. A phylogenetic analysis was conducted based on morphological characters taken from the skull, dentition, and postcranial skeleton. The features were analyzed among taxa of different lineages from the Mesozoic and Cenozoic of Asia, North America, and South America by means of cladistic methodology. The results obtained suggest that Sparassodonta is a monophyletic group basal to, and closely related to, living marsupials and other fossil extinct metatherians (but they are not related to didelphids, or the Australian carnivorous marsupials as previously considered). The sparassodonts are mainly formed by two groups, Hathliacynidae and Borhyaenoidea (including Proborhyaenidae, Thylacosmilidae, and Borhyaenidae), and some basal stem taxa. The pattern of relationships obtained led to review the traditional systematics of the group and to propose a new modified taxonomic list. Based on the cladogram and the known fossil record, ghost lineages for some groups (e.g., Thylacosmilidae, Borhyaenidae) were recognized that are probably revealing deficiency in the fossil record of the Paleogene of South America.