Diagnosis and redescription of Panochthus subintermedius Castellanos (Xenarthra, Glyptodontia) from the Ensenadan (early-middle Pleistocene) of Buenos Aires (Argentina)

Panochthus subintermedius was originally named by Castellanos in 1933, without any diagnosis and no type material designated. In 1936, he briefly described and designated a holotype for this species (MACN-Pv 5130) and subsequently, in 1942, completed the description, but a diagnosis was still lacking. Some authors have considered this species as nomem nudum, but others have accepted its validity since 1942. In this contribution we propose that Castellanos's 1936 paper is the valid name-establishing publication for this species. The holotype includes a large portion of dorsal carapace, the caudal tube, and remains of postcranial skeleton, belonging to a single specimen from the Ensenadan Stage/Age (early-middle Pleistocene) of Buenos Aires, Argentina. In contrast to the original description, new observations of the holotype reveal that the superficial surface of the dorsal carapace osteoderms is ornamented with small polygonal figures without a principal one. This ornamentation differs from that of P. intermedius Lydekker (the only species accepted up to now for the Ensenadan), with a central figure in most of its osteoderms. The caudal tube of P. subintermedius differs from those of the Bonaerian-Lujanian species (middle late Pleistocene-early Holocene), in having a sharper distal end, one apical dorsal figure, and a higher number of central figures along the entire dorsal surface. No caudal tube associated with the carapace of P. intermedius is known. Accordingly, P. subintermedius can be clearly distinguished from other Panochthini species by a unique combination of carapace and caudal tube characters. This new combination of characters provides more information on this taxon and other species of Panochthini for future studies in the interrelationships of Glyptodontia.