Giants of the Pampean plains (Argentina) during Early Pleistocene (Ensenadan).The case of Panochthus (Xenarthra, Glyptodontidae): comparative descriptions

During the Ensenadan (Lower to Middle Pleistocene) cold environments prevailed compared to the previous and successive ones. Up to half of the past century, the Ensenadan was characterized by giant taxa, probably following ecogeographic patterns led by the Bergmann's rule. But subsequent systematic revisions have not always confirmed this hypothesis. Two species of Panochthus are recorded in the Ensenadan of the Pampean Region, both exclusive of this Stage: P. intermedius (the type material) and P. subintermedius. Additionally, two specimens assignable to Panochthus cf. P. subintermedius have also been found in Ensenadan sediments of the Pampean Region. These taxa are considerably larger than their congeneric specimens that lived after the Ensenadan-Bonaerian border. They follow the Bergmann's rule and fulfill the postulate of the Ensenadan gigantism. As well as other Ensenadan megaherbivores, the feeding behavior during this period may account for their large size.