New data on the glyptodontid Trachycalyptoides from the late Miocene Bolivian locality of Achiri.

PUJOS, F.; GONZÁLEZ-RUIZ, L.R; GAUDIN, T.J.; BOSCAINI, A.; ABELLO, M.A.; ANDRADE FLORES, R.; FERNÁNDEZ-MONESCILLO, M.; MAMMANI QUISPE, B.; MARIVAUX, L.; PRÁMPARO, M. B.; ANTOINE, P. O.; MÜNCH, L

Buenos Aires

Congreso; XII Congreso de la Asociación Paleontológica Argentina; 2021

Asociación Paleonológica Argentina

Among armored xenarthrans, Glyptodontidae constitute of the most peculiar and also characteristic group of south American endemic mammals which have lived in this continent since the early Eocene until the arrival of humans. Their evolutionary history is particularly well known in Patagonia, Central and North America, but lesser in the tropics and central South America. In Bolivia during the Neogene period, particularly during the Miocene, this family is only present in the Laventan locality of Quebrada Honda with cf. ?Asterostemma?, ?Propalaehoplophorus? andinus, and two Sclerocalyptinae species, the ?Colloncuran locality of Nazareno with ?Propalaehoplophorus? and ?Neothoracophorus, signaled in Choquecota, and represented in the late Mayoan?early Chasicoan localities of Chokorasi and Achiri by a single species, Trachycalyptoides achirense. The Late Miocene fossiliferous locality of Achiri was discovered in the early 70?s by the French paleontologist Hoffstetter and has been explored by several teams during the following decades. Its mammalian fauna is well diversified with more than 20 taxa including marsupials (i.e., Borhyaenidium), notoungulates (e.g., Hoffstetterius), litopterns, rodents (e.g., Prolagostomus), and xenarthrans sloths (e.g., ?Xyophorus?) and cingulates including Trachycalyptoides. This genus was created by Saint-André in 1996 on the basis on two dermal armors and caudal tubes, an incomplete skull, and an hemimandible. The abundant material collected by our team during recent field works and the preliminary revision of the material housed in the Museums of La Paz and Paris, has allowed us to obtain new information, specifically on the dentition, dorsal carapace, and caudal tube on this peculiar glyptodontid.In Trachycalyptoides, the presence of three lobes in both upper and lower molariforms is well marked especially on the most posterior teeth (eighth to fourth molariforms), doubtful on the third teeth, or absent on the second and first teeth. The general structure of the osteoderms corresponds to a pentagonal or hexagonal polygon with a ?rosette? pattern (a central figure surrounded by peripheral figures) on the exposed surface. The central and peripheral figures are elevated and separated by a sulcus. The subcircular central figure is lightly concave in the center. The peripheral figures are small and in a variable number according to the region (from 3-4 to 12-15) with foramina at the intersection with the sulcus of the central figure. The caudal tube is conical and elongated and its apex is relatively acute. The ventral face is slightly convex and the dorsal face is flat. The distal portion of the tube consist of is conformed by two large right and left osteoderms. The latter are roughly quadrangular, rectangular proximally and quadrate distally. All osteoderms of the caudal tube do not develop peripheral figures. The molariforms, dorsal carapace, and caudal tube of Trachycalyptoides show affinities with glyptodonts that have a simplified trilobation in the anteriormost molariforms, dorsal carapace formed by osteoderms with a ?rosette? pattern and a caudal tube formed by osteoderms without peripheral figures like Cochlops, Palaehoplophorus, Trachycalyptus, and Lomaphorus.