Changes in form and function of the caudal tubes in Panochthus Burmeister, 1866 (Xenarthra; Glyptodontidae) along the Pleistocene

ZAMORANO M.; FARIÑA R.

Simposio; 11ème Symposium of Morphometrics and Evolution of Shape; 2021

Glyptodonts? biochron span from the late Eocene until their demise at the early Holocene. Their palaeobiology has deserved attention lately, including their posture, locomotion and agonistic behaviour. It has been proposed that a bipedal (althouh not erect) posture could have been used in the very large Pleistocene species for using their heavy caudal tubes as weapons, as protection against predators and in intraspecific fights. With 8 species, Panochthus Burmeister, 1866 is one of the most abundant and diverse glyptodont genera during the Pleistocene of South America, as well as one of the largest individuals. The relationship between the shape of the tube and its usage as weapons in the species of Panochthus is explored here. The morphology of the caudal tube is: (1) ≈ conical -cylindrical and (2) hilt-less viking style sword. The form (1) is represented in P. subintermedius Castellanos, 1937 (MACN-Pv 5130), the only full caudal tube known for the time interval early Pleistocene ? middle Pleistocene (Ensenadan). On the other hand, the form (2) is present in the specimens from the middle - late Pleistocene (Bonaeran-Lujanian): P. tuberculatus (Owen, 1845), P. greslebini Castellanos, 1942, P. florensis¬ Brambilla, Lopez & Parent, 2020- P. frenzelianus Ameghino, 1889 is not considered, since its tube is not known nor are P. jaguaribensis (Moreira, 1965) and P. hipsilis Zurita, Zamorano, Scillato-Yané, Fidel, Iriondo & Gillette, 2017, whose findings are known from the Pleistocene (sensu lato)-. The shape of the caudal tube (1) ≈ conical-cylindrical, allows the glyptodon to perform its blows more effectively in all directions; that is, hitting with less precision. Whereas, the form (2) style of Viking sword, has the greater effectiveness in the blows produced in horizontal direction; these blows require then greater accuracy.