Diversityand phylogeny of the Glyptodontidae (Xenarthra, Cingulata) from the Chasicoaim stage/age (late Miocene) of Argentina

Abstract

Agreatdiversity of Glyptodontidae (Xenarthra, Cingulata) has been mentioned forthe Chasicoan Stage/Age (late Miocene), particularly in the Pampean región of Argentina, induding representativas of thetribes Palaehoplophorini, Plohophorini, and "Sclerocalyptini". In this contribution, we carried out a detailed revisión induding the most complete specimens known for this lapse: 1) PV-UNS-260, from Arroyo Chasicó Formation (Buenos Aires Province), composed of fragmented skull, almost complete dorsal carapace, caudal tube with first ring, and rlght fémur; and 2) PVSJ-366, from Loma de Las Tapias Formation (San Juan Province), composed of almost complete skull, dorsal carapace fragments and caudal rings. Both specimens develop dorsal carapaces with a uniform ornamentaron pattern ("rosette pattern") and a similar caudal tube morphology. Additionally, other specimens of this lapse are mainly represented by isolated osteoderms, which also show the same ornamentation pattern. Our comparative study suggests, contrary to the high diversity previously mentioned, the presence of a single morphotype for this lapse, which would represent a new taxonomic entity that, for the moment, cannot be assigned to the known tribes. This better anatomical characterization allowed to inelude Chasicoan glyptodonts into a morphological phylogentic analysis for the first time. Obtained results place them as sister group of all the following Neogene and Quaternary diversity, condition supported by the development of a unique caudal tube morphology, representing the first appearance of some derived characters in this structure, such as peripheral figures and lateral figures increasing their size towards the apex.