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

Abstract

With eight species, Panochthus is one of the most abundant and diverse glyptodont genera during the Pleistocene of South America, as well as one of the largest glyptodonts. The relationship between the shape of the tube and its usage as weapons in the species of Panochthus is explored here; moreover, we intend to assess how they evolved among the species of the genus Panochthus. 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 from Early Pleistocene–Middle Pleistocene (Ensenadan). The form (2) is present in the specimens from the Middle–Late Pleistocene (Bonaerian-Lujanian): P. tuberculatus, P. greslebini, P. florensis. P. intermedius, P. frenzelianus, P. jaguaribensis and P. hipsilis is not considered. The shape of the caudal tube (1) allows the glyptodont to perform its blows more effectively in all directions; which implies hitting with less precision. Whereas, the form (2) style of Viking sword, has the greater effectiveness in the blows delivered in a horizontal movement that requires greater accuracy. In the more recent species of Panochthus, those that show the form (2) present also more ornamentations that were possibly covered by corneous structures.