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.
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Vol. 38 • No. 3