TWO NEW MACRAUCHENIIDS (MAMMALIA: LITOPTERNA) FROM THE LATE MIDDLE MIOCENE (LAVENTAN SOUTH AMERICAN LAND MAMMAL AGE) OF QUEBRADA HONDA, BOLIVIA

We describe two new macraucheniid litopterns from the late middle Miocene (ca. 13 Ma) Quebrada Honda Fauna of southern Bolivia. The holotype of 'Theosodon' arozquetai, sp. nov., is a partial cranium preserving RI2–M3 and LP1–M3, elements of the hind limb, and two metapodials. An upper cheek tooth series is also referred to this species. The holotype of Llullataruca shockeyi, gen. et sp. nov., is a mandible preserving nearly the entire lower dentition. A dentary, several upper teeth, and a variety of postcranial elements are also referred to this species. Two specimens from the slightly older locality of Cerdas, Bolivia, are assigned to L. cf. shockeyi. A phylogenetic analysis recovers 'T.' arozquetai as sister to Theosodon spp., and we provisionally refer it to that genus pending its revision. Llullataruca shockeyi forms a polytomy with three late Oligocene—early Miocene 'cramaucheniines' and the later-diverging macraucheniids. The body mass of 'T.' arozquetai is estimated at 80.8–116.2 kg, slightly smaller than early Miocene T. garretorum. Llullataruca shockeyi is among the smallest known macraucheniids based on dental dimensions and is estimated at 35.3–54.6 kg. Theosodon' arozquetai and L. shockeyi are the first well-characterized macraucheniids from the middle Miocene, and the latter species demonstrates that relatively early-diverging lineages persisted at least 7 million years longer in tropical latitudes than they did in Patagonia.