Résumé
Glyptodontidae are giant armored xenarthrans characteristic of the endemic Cenozoic mammalian fauna of South America. Our knowledge of their evolutionary history among cingulates mainly relies on taxa from the Austral region (Patagonia) of the continent, whereas tropical and intertropical forms remain poorly known. The Late Miocene Achiri local fauna, La Paz Department, Bolivia, has yielded iconic taxa such as the horned toxodontid Hoffstetterius imperator, the ground sloth Mcdonaldocnus bondesioi, and the frog Telmatobius achachila. Trachycalyptoides achirense is a large glyptodontid (~200 kg) endemic to Achiri that was preliminarily described in the late 1990s. This peculiar hoplophorine (i.e., glyptodonts with caudal tube) shows strong affinities with the coeval genus Kelenkura from the Arroyo Chasicó locality in Buenos Aires Province, Argentina. Trachycalyptoides is characterized by several cranial, postcranial, and carapace autapomorphies, including: (i) a short, broad muzzle; (ii) a very gracile greater trochanter of the femur; (iii) central figures of the dorsal carapace osteoderms that are concave, occupying most of the dorsal surface; and (iv) the complete absence of peripheral figures in the osteoderms of the caudal tube. The peculiar morphology of the snout is likely related to the marked lateral expansion of the maxillary region from Mf1 to Mf6, a unique feature among Hoplophorinae. Within this group, our phylogenetic analysis places Trachycalyptoides and Kelenkura as sister taxa, both representing basal Plohophorini. Our preliminary results also indicate that plohophorines were the dominant group of Neogene glyptodonts in the Bolivian Andes, representing the only clade occurring at other localities such as Quebrada Honda (Middle Miocene, taxa currently under study) and Pomata-Ayte (Late Miocene, Stromaphorus sp.). However, the large number of autapomorphies observed in Trachycalyptoides, compared with other plohophorines, strongly suggests some degree of isolation of the Achiri fauna, as further supported by the presence of several endemic taxa at this locality.