A review of the molar morphology and phylogenetic affinities of Sillustania quechuense (Metatheria, Polydolopimorphia, Sillustaniidae), from the early Paleogene of Laguna Umayo, southeastern Perú

LAURA CHORNOGUBSKY; FRANCISCO J. GOIN

JOURNAL OF VERTEBRATE PALEONTOLOGY

SOC VERTEBRATE PALEONTOLOGY

Lugar: Lawrence; Año: 2015

0272-4634

The early Paleogene mammalian assemblages known from the red mudstones of the Lower Muñani Formation at Laguna Umayo, southeastern Perú, add significant information on the early phases of the evolution of Metatheria in South America. Two early Cenozoic vertebrate associations have been found from the Laguna Umayo area: localities LU-3 and Chulpas, both including metatherians. The LU-3 locality provided Peradectes austrinum, at least two indeterminate didelphimorphians, and a ?Pediomyidae or ?Microbiotheriidae indet. The Chulpas local fauna includes at least three indeterminate didelphimorphians and three polydolopimorphians: Chulpasia mattaueri, Chulpasia jimthorselli, and Sillustania quechuense. The Laguna Umayo associations have alternatively been referred to the Late Cretaceous or the early Paleogene. Grambast et al. (1967; see also Sigé, 1971) assigned the Chulpas levels to the Vilquechico Formation (Maastrichtian) because it was correlated with deposits containing charophytes and dinosaur eggshells. More recently Sigé et al. (2004) favoured a younger age for the LU-3 and Chulpas localities: late Paleocene-Early Eocene, probably coincident with the Itaboraian SALMA. We follow Woodburne et al (2014) for the calibration of the early Paleogene SALMA´s. The highly derived, enigmatic morphology of the only known upper molar of Sillustania quechuense granted the recognition of a new family of South American metatherians: Sillustaniidae. Crochet and Sigé (1993) preliminary assumed that Sillustania was probably a caenolestoid paucituberculatan, but in their formal description they recognized the Sillustaniidae as a new family belonging to the polydolopoid polydolopimorphians. A review of the holotype and tentatively referred specimen of Sillustania quechuense led us to reassess its upper molar morphology and homologies, as well as its phylogenetic affinities. The discussion of these aspects constitutes the main purpose of this work.