Neoichnology of armadillos: Keys for the paleoecological and behavioral interpretation of fossil tetrapod burrows

Abstract

This study is based on the analysis of burrow casts of three species of armadillos from central Argentina: Chaetophractus villosus, Chaetophractus vellerosus, and Zaedyus pichiy (Chlamyphoridae: Euphractinae). The aim of this work was to identify key ichnologic signatures of Euphractinae armadillo burrows for application to the paleoecological and behavioral interpretation of fossil examples. A total of 15 active burrows from different biogeographic provinces were casted with polyurethane foam and then excavated. About two hundred uncasted burrows and foraging pits were also measured at the same localities. Euphractinae burrows are clearly distinguished from Chlamyphorinae burrows by its filling, surface ornamentation, and size. It is suggested that fossil armadillo (Euphractinae) burrows would be characterized by a single ramp with one entrance and massive or laminated fill, horizontal diameter larger than 100 mm, strongly marked sets of three claw traces that are arranged oblique to the ramp axis, and absence of feces or plant remains. The distinctive surface ornamentation present in the casted burrows is tentatively linked to a particular excavation mechanism involving rotation of the body along the antero-posterior axis. Burrow systems with a chamber are interpreted as permanent burrows, whereas those lacking chamber are considered as temporary/shelter burrows. Armadillo burrow systems (either temporary or permanent) are longer, less inclined, and have lower relative diameter indices (RDI) than armadillo foraging pits. Euphractinae burrows are linked to producers with solitary, fossorial, opportunistic omnivorous habits that excavate several burrows during their lives. They are left open after abandonment, and preferably located in xeric shrub lands and grasslands. The described morphological features of the burrows systems can be useful for the interpretation of fossil (post-Eocene) burrows.