Abstract

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 on a single specimen from the middle Miocene Quebrada Honda local fauna of southern Bolivia. This specimen (UF 27881) does not clearly correspond to any major sparassodont group (e.g., Hathliacynidae, Borhyaenidae, etc.) and represents a morphotype previously unknown among the Sparassodonta. UF 27881 is distinguished from other sparassodonts by its short, broad, borhyaenid-like rostrum and small size, among other features. However, we decline to coin a new name for UF 27881 due to the fragmentary nature of this specimen and the absence of most of its dentition. This specimen suggests that the appearance of the Sparassocynidae and several hypercarnivorous didelphid taxa (including Thylophorops, Thylatheridium, Lutreolina, and Hyperdidelphys) represent an evolutionary response to the decline in small, predatory sparassodont taxa during the late Cenozoic. This study documents new morphological diversity among the Sparassodonta and highlights the value of fossils from traditionally undersampled parts of South America.