Juvenile glyptodonts (Mammalia, Xenarthra, Cingulata) from Cerro Zeballos (Collón Curá Formation, Middle Miocene), Chubut, Argentina

Abstract

The diversity of glyptodonts has been overestimated because many genera and species have beenrecognized on characters from osteoderms and carapaces without considering the variation of different regions of the carapace or the ontogenetic variation of the osteoderms. The present contribution aims to describe juvenile glyptodonts specimens that were collected from the fossiliferous locality Cerro Zeballos of the Collón Curá Formation, northwestern Chubut Province, Argentina. At this locality the only previously recorded glyptodont is Paraeucinepeltus raposeirasi, mainly characterized for a central conical elevation in the cephalic shield osteoderms. Specimens studied are housed at the Laboratorio de Investigaciones en Evolución y Biodiversidad (LIEB) from the Universidad Nacional de la Patagonia "San Juan Bosco". LIEB-PV 6070 is represented by 65 osteoderms of the dorsal carapace, two vertebrae, eight rib fragments, right tibia, left petrosal, and occipital fragment; LIEB-PV 6175 is represented by 125 osteoderms from the dorsal and caudal carapace; LIEB-PV 5348 is represented by one osteoderm fragment of the cephalic shield; LIEB-PV 6072 is represented by one osteoderm of the cephalic shield; and LIEB-PV 6059 is represented by one cervical tube fragment and five osteoderms of the dorsal carapace. The absence of central and peripheral figures of the osteoderms, the presence a punctuated exposed surface and smooth lateral surfaces enables the distinction of an early juvenile stage (LIEB-PV 6070); while the presence of poorly marked central and peripheral figures of the osteoderms, a slightly smooth exposed surface and generally developed sulci suggest a late juvenile stage (LIEB-PV 6175, LIEB-PV 6059, LIEB-PV 5348, and LIEB-PV 6072). All specimens are assigned to cf. Paraeucinepeltus raposeirasi. Although, the juveniles do not yet present completely developed adult characters, they were found associated with adult specimens (e.g., LIEB-PV 6064 and LIEB-PV 6042) of the mentioned species. In addition, two specimens (LIEB-PV 5348 and LIEB-PV 6072) have the central conical elevation of the osteoderms of the cephalic shield. The recognition and description of juvenile specimens of glyptodonts have the potential to contribute with information about ontogenetic variations in osteoderms, skulls, and postcranial skeleton, avoiding synonyms based on juvenile specimens.