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.

The type material of Tisoa siphonalis de Serres, 1840 is lost but nearly complete specimens occur at the herein designated type locality Hameau de Valz (Department of Gard, France), where Tisoa is present in dark Pliensbachian organic-rich mudrock. The upper part of the trace is encased in a concretion. The concretion's carbonate content implies 65% initial porosity, a value typical of soft mud. Such a consistency is also indicated by shallowly produced biodeformational structures that dominate the fabric; in association with small traces they are diagnostic of low-oxygenated bottom water and anoxic conditions just below the seafloor. At its type locality, Tisoa represents a nearly vertical protrusive spreite burrow, exceeding 2 m in length and having nearly parallel limbs 0.1–1.5 cm apart. The spreite is only weakly expressed; the inter-limb material was apparently not processed during deepening of the U-tube but placed directly in the spreite or pressed aside. Tisoa deviates slightly but consistently from a vertical orientation and commonly shows a low-amplitude helicoidal course. The U-tube exhibits a thick pyrite lining implying the former presence of mucus. The steep chemical gradient between oxygenated water in the U-tube and anoxic host sediment evidently fostered microbial activity. The extraordinary penetration depth of Tisoa suggests exploitation of extreme redox conditions such as could be found in the methanogenesis zone. The Tisoa producer probably deepened the U-tube incrementally, continuing when the chemical gradient between tube and host sediment declined due to circulation of the oxygenated water used for respiration. The Tisoa producers might have fed on suspended material, microbes flourishing along the tube wall, or acquired nutrition via chemosymbionts.

An array of trace fossils have been ascribed to brittle-star behaviors including locomotion traces such as Biformites. Brittle-star locomotion has been well described but little work has been done to link modern brittle-star behavior to the trace fossil record. To draw this connection, a brittle star was kept in an aquarium and isolated in a “walking” tank with a fine glass-bead substrate. The animal was left in the walking tank for 30 minutes then the substrate was examined for traces. A digital camera was used to record the animal's movements and to document the resulting traces. Photographs were processed with photogrammetry software to produce digital models in order to acquire high-resolution images. Walking traces were described in detail and two morphologies were identified, which correspond with the ‘rowing’ and ‘reverse-rowing’ modes of brittle-star locomotion. Interestingly, traces similar to Biformites were not formed although some Biformites characters are observed. Morphological similarities include elongated lobate depressions and bioglyphs. Trackway dissimilarities include a repeating, paired, symmetrical pattern observed in the lab contrasting with Biformites that is often expressed as a texture of dense and overlapping, or isolated imprints. Another dissimilarity is the expression of bioglyphs in the lab as striae compared to the positive protuberances observed in Biformites. This study illustrates the utility of using actualistic observations to: (1) refine interpretations of locomotory mechanisms, such as rowing and reverse rowing, for a better understanding of walking behavior, and (2) to expand recognition criteria for ophiuroid (and other taxa) tracks in the fossil record.