Damaged armour: Ichnotaxonomy and paleoparasitology of bioerosion lesions in osteoderms of Quaternary extinct armadillos

Abstract

Osteoderms are dermal ossifications present in several vertebrates and assemble a carapace on armadillos. Here we describe ichnotaxonomically two types of bioerosion traces as well as paleopathologically ulcerative lesions on osteoderms of three specimens of Late Pleistocene Holmesina cryptae armadillos (Xenarthra, Cingulata, Pampatheriidae) found in Lapinha Cave, Iramaia municipality, Bahia State, Brazil. The traces are always on the external surface of the osteoderms, none on endoskeleton elements, which are also different from bites and taphonomic process marks. This is evidence of the biological and syn vivo origin of the traces, making them remarkable and useful to access animal health. Karethraichnus minimum isp. nov. are individual holes interpreted as produced by sand flea sessile females, probably from the Tunga genus, based on already described lesions in living armadillos. This trace reveals a paleoparasitism behavior useful for tracking this relation deep in time in armoured animals. Violinichnus punctatus igen. et isp. nov. is formed by consecutive tiny holes, forming an overall elliptical/violin-like shape. This is attributed to lesions produced by the action of fungi over osteoderms, similar to mycose-like dermatophytosis (ringworm) in modern mammal skin. In contrast, the ulcerative lesions are recorded as necrosis of bone material, producing a corrosive-like disruption on the external surface of the osteoderms formed by irregular pits and exposition of spongy bone. These are ulcerative lesions probably produced by secondary infections by microorganisms such as fungi or bacteria, or even a destructive immunological response. This would begin as a more restricted lesion with several potential agents for this: abrasion from the soil, plants; lesions from intraspecific fights or predation; dermatitis; ectoparasites (e.g., mites, ticks, fleas, mosquitoes) or initial mycosis or bacterial infection. Since a bioerosive process cannot be demonstrated and is rather unlikely for the ulcerative lesions, these structures are not considered trace fossils. It is reasonable to assume that the flea lesion Karethraichnus minimum isp. nov. and fungal lesion Violinichnus punctatus igen. et isp. nov. could lead to an ulcerative lesion. As syn vivo traces, all these are tools to access the health of the animals to which the osteoderm belongs. Further support on ectoparasite and infection studies on living armoured animals would even allow inferences regarding extinct populations and interpretations of ancient ecosystems.