TETRAPOD BURROWS IN THE EARLY MIDDLE TRIASSIC TARJADOS FORMATION, ARGENTINA: ORGANISM RESPONSES IN SEMI-ARID SEASONAL CLIMATES

KRAPOVICKAS VERÓNICA; MANCUSO, A.; MARSICANO, C.A.; DOMNANOVICH, N.S.; SCHULTZ, C.

Congreso; IV Congreso Latinoamericano de Paleontología de Vertebrados; 2011

Large burrows are recorded in the early Middle Triassic Tarjados Formation, at Talampaya National Park, La Rioja province, Argentina. Facies analysis indicates that they are preserved in sandbars of ephemeral fluvial systems developed under a semi-arid seasonal climate. The structures are mostly recorded in longitudinal cross-section and consist of a mold of an opening, a main ramp and a terminal chamber. The main ramp is 8 to 14 cm in height, 49 to 63 cm deep with an inclination of 30° to 45°, and up to 130 cm in length. We studied the burrow dimensions, the overall architectural morphology, and the presence of surficial marks to compare them with other large burrows of both invertebrate and vertebrate origin. As a result, the Tarjados burrows are interpreted as produced by tetrapods, and the possible tracemaker was identified using: (1) body fossils preserved within other Upper Permian and Triassic burrows, (2) functional morphology of anatomically defined burrowers, and (3) records of putative burrowers in stratigraphically equivalent outcrops. The analysis suggests that the Tarjados structures were most-likely produced by non-mammalian cynodonts. Comparison with other Upper Permian and Triassic tetrapod burrows allowed the identification of three generalized morphological groups: (1) burrow network complexes, (2) helical burrows, and (3) simple inclined burrows, each of which represents different behaviors. In Gondwana, the environmental and climatic context in which Lopingian (Upper Permian) and Early-Middle Triassic burrows are preserved suggest that aridity and seasonality played a fundamental role in the evolution of burrowing behavior, at least among therapsid.