New remains of Doedicurini (Cingulata, Glyptodontidae) from the latest Pliocene/earliest Pleistocene of the Pampean Region (Argentina) shed light on the morphological evolution of the caudal tube

Glyptodonts are probably among the most iconic and enigmatic mammals that ever lived during the Cenozoic of America. One of the main clades, Hoplophorinae, developed since the Miocene a structure unique within mammals, the caudal tube, composed of the union of the distal most caudal rings of the caudal armor. In some taxa, especially in the Late Pleistocene species, the caudal tube suffered significant morphological changes. One extreme case is represented by the giant-sized Doedicurini Doedicurus clavicaudatus, in which the caudal tube is transformed into a kind of “clave” (ie., a widening of the distal part, and some large lateral figures where corneal “spine-like” structure were inserted). It has been suggested that this was used in intraspecific combat rather than having a defensive function. Despite this, almost nothing is known about the morphological evolution of this structure along the evolutionary history of Doedicurini. The finding of new remains of Eleutherocercus sp. (a partial caudal tube and dorsal carapace) from the El Polvorín Formation at the Plio/Pleistocene boundary in the surrounding of Olavarría (Buenos Aires province, Argentina), allow us a better understanding of the morphological evolution of this structure between the Late Miocene/Pliocene Eleutherocercus spp. (ca. 7–2.6 Ma) and the Late Pleistocene Doedicurus clavicaudatus. The extreme modification in D. clavicaudatus involves, among others, the disappearance of the most proximal lateral figures, an increase in the diameter of the I Lat figures and disappearance of the II and III Lat figures; and increase in size and lateralisation of the dorso-ventral pairs (especially the 1st pair).