Interconnected chambered trace fossils, Pliocene lower Tipam Formation, Tripura, India

Abstract

A new kind of trace fossil characterized by filled ellipsoidal chambers interconnected by a boxwork of burrows, shafts and tunnels, in different horizontal planes, is observed in the medium-grained fluvial sandstone of the Pliocene Lower Tipam Formation in the Amarpur area of Tripura in northeast India. The chambers have variable dimensions with lengths of 3–16 cm, widths of 3–10 cm and heights of 2–6 cm. Diameters of the connecting tunnels and shafts are 0.8–0.9 cm on average. The traces are considered to be nest systems of social insects. The discovery is noteworthy as far as the geology of Tripura state is concerned, as such chambered traces have not previously been reported from the Indian sub-continent. Morphology of the studied specimens point toward a new ichnospecies, Vondrichnus amarpurensis isp. nov. of the ichnofamily Krausichnidae.