Memories of the blows: severe soft-tissue injuries in caudal vertebrae of Panochthus Burmeister (Xenarthra, Glyptodontidae)

Abstract

Bone pathologies have great potential to provide information on the palaeobiology of fossil organisms. Some were likely related to inter/intraspecific fighting behaviors. Among the iconic and conspicuous Late Pleistocene armored mammals, Panochthus Burmeister, 1866 is notable for being one of the largest, most abundant, and diversified genera. A particular feature of Panochthus species is the presence of a caudal armor including a solid bony structure known as a caudal tube that would have played an important role in intra/interspecific contests. In this contribution, we report and describe a caudal vertebra of Panochthus that shows strong evidence of pathologies that may be related to the performance of strong tail movements that could correspond to offensive/defensive behaviors. The specimen (MFA-G-PV 1740) was recovered from Late Pleistocene deposits (MIS 5–3 cycles) cropping out in the cliffs of Northern Salado River, Santa Fe Province, Argentina. Based on morphological and radiological features, the lesions observed are related to a traumatic lesion that would have affected the ligamentum flavum and probably the articular capsule of the postzygapophysis, generating a severe enthesopathy and related septic arthritis. The involvement of this ligament in particular is crucial because it connects adjacent vertebral laminae and restricts mobility, offering resistance to extreme vertebral flexion and protecting the remaining vertebral structures when confronted with large forces. Although it is challenging to determine the exact way in which this species performed fighting tail movements, the joints with the greatest range of movement correspond to the most anterior caudal vertebrae. This also implies that any strong impact would have directly affected these vertebrae and associated soft tissues, including ligaments. Based on this evidence, we consider that the pathology described here represents strong evidence to support the idea of an active use of the caudal tube in Panochthus.