Role of environmental change in rock-boring echinoid trace fossils

Abstract

Abstract Well preserved groove-borings related to the boring activity of regular sea urchins are preserved on Neogene rocks associated with rocky palaeoshores in a volcanic oceanic island (Santa Maria, Azores archipelago) and a continental margin (Foz da Fonte, Central West Portugal). The new trace fossil consists of a series of relatively deep grooves, with sinuous pathway and with a fairly uniform width along its trajectory. A series of forward oriented concave markings occur frequently inside the grooves, reflecting the movement direction of the producer. The trace fossil is designated as Ericichnus igen. n. with two new ichnospecies, Ericichnus bromleyi isp. n. and Ericichnus asgaardi isp. n. Ericichnus igen. n. could have been produced by regular echinoids, similar to the extant echinometrid echinoid Echinometra lucunter ( Linnaeus, 1758 ) for E. bromleyi isp. n. and similar to the echinid Paracentrotus lividus Lamarck, 1816 for E. asgaardi isp. n. Ethologically, the compound trace fossil Ericichnus igen. n-Circolites may correspond to an agrichnion–pascichnion and/or domichnion. Our study suggests that the new ichnospecies E. bromleyi may be used as a palaeoenvironmental tool, indicating the boring activity of termophile rock-boring echinoids in the fossil record.