Anatomy of the most reinforced caudal tube in an enigmatic specimen of Panochthus (Xenarthra, Glyptodontidae): chronology and paleoenvironmental implications, and taxonomic revision of Panochthus florensis

Abstract

Panochthus Burmeister, 1866 (Xenarthra, Glyptodontidae) is one of the most abundant and diverse glyptodont genera during the Pleistocene of South America. It is also among the largest members of the family and, together with Glyptodon Owen, 1839, exhibits the broadest latitudinal and altitudinal distribution across the continent. Currently, eight species of Panochthus are recognized: P. tuberculatus (Owen, 1845), P. frenzelianus Ameghino1889, P. intermedius Lydekker1895, P. subintermedius Castellanos1937, P. greslebini Castellanos1942, P. jaguaribensis (Moreira, 1965), P. hipsilis Zurita et al.2017, and P. florensis modified by Brambilla, Lopez and Parent, 2020—six of which are present in the Pampean Region. This study describes a caudal tube from the Late Pleistocene attributed to Panochthus sp., which exhibits a set of distinctive features (e.g., presence of an apexial figure, two apexian figures, terminal figures with distally oriented projections, and five or six large sub-elliptical figures delimited by prominent ridges) and a novel combination of characters (e.g., simultaneous presence of apexian and more than one apical figure, dorsal apical figures, asymmetrical and symmetrical ventral apical figures, among others). These traits suggest that this caudal tube represents the most reinforced example known for the genus. Based on several anatomical similarities, P. jaguaribensis, and P. greslebini appear to be closely related to the material described herein. Additionally, we propose reassigning the holotype caudal tube of P. florensis to Panochthus sp. and consider P. florensis a species inquirenda.