Direct and indirect evidences of microorganisms related with tetrapod remains from the Triassic

PREVITERA, MARÍA ELENA; BENAVENTE, CECILIA ANDREA; ARCUCCI, ANDREA; MANCUSO, ADRIANA CECILIA; IRMIS, RANDALL

Congreso; 11° Congreso de la Asociación Paleontológica Argentina; 2016

The Chañares Formation represents a fluvial environment with significant development of its floodplain where the abundant and rich Chañares Fauna lived. A new absolute date constrains the Chañares to the Early Carnian, therefore expanding the time between the PT boundary, recorded in the Talampaya Formation, and the firts rich Triassic fauna in the IVU Basin. The Chañares Formation includes an abundant and rich tetrapod record with an extraordinary well-preservation, both in concretion as well as out of them. New studies reveal evidence of microorganism associated with tetrapod remains. We observe corrosion at the bones from a carcass found in the floodplain sediments. The corrosion is the result of indirect action of aerobic decay organisms that created a microenvironment in subaerial deposition and chemistry that exacerbated the corrosion during pre-burial. In addition, we have observed the presence of clotted micrite in the surrounding sediment of the carcass. The presence of clotted micrite suggests that heterotrophic anaerobic/aerobic bacteria affected the chemical composition of the matrix immediately in contact with the bone remains triggering the alkalinity engine ultimately leading to calcite precipitation. This indirect evidence is furthermore supported by the presence of coccoid structure found in tetrapod coprolites, that would represent fossils of microbial origin most probably coccoid Gram-negative bacteria, which are dense populations inhabiting the intestines of living vertebrates.