Guangyuanichnus majianus n. igen. n. isp., a large, complex burrow system from the Lower Devonian Pingyipu Formation of the northwestern Yangtze platform, South China

Abstract

A large, three-dimensional burrow system with a maximum vertical extension of 34 cm and a maximum covering area of 40 × 50 cm is reported from the Lower Devonian Pingyipu Formation of the northwestern Yangtze platform, South China. The burrow system, erected as Guangyuanichnus majianus n. igen. n. isp., is composed of two elements, i.e., a basal part that consists of several arcuate burrows, and an upper part emerging from the distal part of each arcuate burrow, which consists of radial, horizontal to subhorizontal spreite bodies in multiple levels in the substrate. The morphologic and taphonomic features of the basal and upper parts, the comparison of ecological and behavioral characters as well as the resulting burrows among various groups suggest that the burrow system was probably constructed by an unknown group of deposit-feeding bivalves. These animals burrowed to a medium to deep tier in the shoreface setting, where they constructed the basal arcuate burrows, and extended the agile siphon far out of the burrow to systematically exploit surficial materials for consumption. The behavior of the tracemaker and resulting trace fossils closely resemble those of modern and ancient tellinacean bivalves, which most likely represents a behavioral convergence. G. majianus probably represents some of the earliest bivalves that occupied a relatively deep tier and conducted a siphon-feeding strategy, a functional innovation well prior to the radiation of siphon-feeding infaunal bivalves during the Mesozoic. The presence of G. majianus suggests that large, deep burrowers tended to cause more dramatic impacts in substrate properties than other major Paleozoic bioturbators, and that they could be responsible for the elevated environmental effects of bioturbation as has been observed in strata younger than the latest Silurian.