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The Sparassodonta (Mammalia, Metatheria) are a group of carnivorous mammals that dominated the macropredatory guild of South America during the Cenozoic. Here, we describe a new sparassodont based ...

Deltatheroida is a small, mostly Asian, clade of Cretaceous mammals with a complicated systematic history and a poor North American fossil record. The recently described latest Cretaceous Nanocuris improvida is a relatively large, morphologically distinctive taxon with carnivorous adaptations; it was tentatively referred to its own family Nanocuridae within Eutheria. Here, we describe a new specimen from the uppermost Cretaceous Lance Formation of Wyoming that is referable to Nanocuris improvida, the second occurrence for the taxon. New morphological information from the specimen allows us to refer five additional Lancian specimens, some of which have been previously described as deltatheroidans, to Nanocuris improvida and ?Nanocuris sp. Results from a phylogenetic analysis remove Nanocuris from Eutheria and reveal strong support for its deltatheroidan affinities and for its nested position within Metatheria. As a result, we subsume Nanocuridae within the deltatheroidan family Deltatheridiidae. W...

Partial crania of two fossil species of koala (family Phascolarctidae) from Oligo-Miocene deposits in the Riversleigh World Heritage Area, one referable to Litokoala kutjamarpensis and another to Nimiokoala greystanesi, are described. Comparison with the extant koala Phascolarctos cinereus and other diprotodontian marsupials reveals a high degree of similarity in basicranial morphology between fossil and modern phascolarctids but substantial differences in the architecture of the masticatory system. Key specialisations present in Phascolarctos but absent in both Litokoala and Nimiokoala include forward displacement of the palate, enlargement of the occlusal surface of the molar teeth, thickening of the maxillae above the toothrow with resultant lowering of the occlusal plane of the cheekteeth relative to the glenoid fossa, and a decrease in the size of the pterygoid fossae. These extreme aspects of the cranial morphology of Phacolarctos probably reflect its dependence on eucalypt leaves, a nutrie...

A new species of Hathliacynidae (Sparassodonta, Metatheria), Acyon myctoderos, from the middle Miocene of Quebrada Honda, Bolivia, is described. This new species is the largest known hathliacynid. Compared to the type species of the genus, A. tricuspidatus, Acyon myctoderos differs in having: (1) longer diastemata among premolars; (2) p2 comparatively more robust, with a better developed posterior cusp and with a sharp anterior crest; (3) lower molars with a more poorly developed anterobasal cingulum; (4) m1–m3 with hypoconulids less salient posteriorly and more vertically oriented; and (5) larger hypoconids at least on the m2. A phylogenetic analysis including nine taxa of Sparassodonta, with Mayulestes as the outgroup, showed that Acyon is more closely related to Cladosictis than to any other hathliacynid.

The skull and skeleton of the Mongolian Late Cretaceous (Barungoyotian) marsupial Asiatherium are described, illustrated, and compared to various therian taxa. The study supports the distinctness of Asiatherium from deltatheroidans and eutherians, and the metatherian status (sensu stricto) of asiatheriids, based primarily on the dental formula, but also on cranial, dental, and postcranial characters. Its postcanine dental formula (three premolars and four molars), found only in dentally primitive living marsupials, is shown to be a derived condition within the Theria (tribosphenic mammals, sensu stricto). In addition, the closely twinned hypoconulid and entoconid, correlated with a (relative) hypertrophy of the metacone, an alisphenoid component to the bulla (possibly an independently derived trait), oval (not elliptical) fenestra vestibuli, and an elliptical fenestra cochleae, along with other unmistakenly marsupial-like (and therian as well as pre-therian) postcranial taxonomic properties, all ...

Ten isolated petrosals of Late Cretaceous marsupials belonging to three types—A, B, and C—are described from the Lance Formation of Wyoming and the Bug Creek Anthills of Montana. These are compared...

A new species of Sparassodonta (Mammalia, Metatheria), Lycopsis padillai, sp. Nov., is described on the basis of a partial left maxilla with M1-M4 and fragments of lacrimal and jugal. The material comes from the early to early middle Miocene Castilletes Formation, La Guajira Peninsula, Colombia. This specimen represents the northernmost record of a fossil metatherian in South America and integrates a highly diverse vertebrate association, recently discovered in the north of Colombia. The La Guajira specimen is referred to the genus Lycopsis, as supported by the results of our phylogenetic analysis. This analysis also demonstrates that species of Lycopsis (L. torresi, L. longirostrus, L. viverensis, and L. padillai) constitute a monophyletic group and are placed as the basal taxon of Borhyaenoidea. Lycopsis padillai is a large-sized sparassodont with a body mass of about 22 kg. The presence of Lycopsis from La Guajira extends the geographical distribution of the genus to the entire South America, representing the sparassodont with the widest latitudinal distribution. Fil: Suarez Gomez, Sandra Catalina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Forasiepi, Analia Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Goin, Francisco Javier. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Jaramillo, Carlos. Smithsonian Tropical Research Institute; Panamá