Experimental analysis of humic acid-induced modifications in armadillos osteoderms

TOMASSINI, RODRIGO; MONTALVO, CLAUDIA; MARIN-MONFORT, MARÍA DOLORES; GARRONE, MARIANA; FERNÁNDEZ, FERNANDO; NAHUEL RUIZ, GABRIEL; KIN, MARTA

Congreso; 5th Palaeontological Virtual Congress; 2025

Palaeontological Virtual Congress

Armadillos (Cingulata, Mammalia) are a distinctive group of xenarthrans from the New World with a long evolutionary history. Their remains are very abundant in archeological and paleontological sites from the Cenozoic of South America. Their representatives are characterized by having a skeleton covered by an armor composed of osteoderms — ossified dermal tissues — which are valuable diagnostic elements in taxonomic and phylogenetic studies of fossil armadillos. The exposed surface of osteoderms exhibits various distinguishing features, including shape, ornamentation patterns (e.g., figures, sulci, dorsal foramina), and the number, size, and location of piliferous foramina. Despite their importance, few taphonomic studies have examined how these original features are altered by biostratinomic and fossildiagenetic processes. We present here the results of a controlled laboratory experiment simulating burial conditions in soil to evaluate the effects of humic acids on the osteoderms of the Large Hairy Armadillo Chaetophractus villosus (Chlamyphoridae). Osteoderms were immersed for three years in plastic containers with varying concentrations (3% to 100%) of commercial humic acid. Observed modifications included progressive loss of compact tissue and exposure of spongy tissue, edge rounding, sulci deepening, and an increase in foramina size. No relationship was detected between acid concentration and the intensity of these alterations during the experiment. This actualistic experimentation provides insights into the taphonomic processes affecting osteoderms during the post-burial stage in pedogenetic environments, and help to be differentiated from other possible processes that modify their structure (i.e., ectoparasitism, predation). It also highlights the potential impact of these changes on the taxonomic identification of fossil specimens.