Mechanism and process of construction of tubes of the trace fossil Schaubcylindrichnus coronus Frey and Howard, 1981

Schaubcylindrichnus coronus is a common trace fossil occurring in post-Cretaceous shallow marine deposits. It consists of a sheaf or bundle of thickly lined tubes, with the tube linings usually composed of colorless minerals (“mineral-lined” type). Recently, many peculiar specimens of S. coronus, whose tube linings are composed mainly of tests of the larger benthic foraminifer Operculina complanata japonica (“Operculina-lined” type), have been found in the inner shelf deposits of the late Miocene Kaichigo Formation in the Miyazaki Group, southwestern Japan. The “Operculina-lined” specimens occur in association with funnel-shaped concentrations of Operculina tests. In some specimens, the end of the tube directly connects to the concentration. We consider these concentrations to be the product of feeding funnels filled with Operculina tests that were delivered from shallower marine settings in association with storm currents. Considering the fact that no Operculina tests are found in the host rocks that bear Operculina-lined tubes, the Operculina tests that line the tubes appear to have originated from Operculina test concentrations. In other words, during feeding, the animal producing S. coronus apparently selected the tests in its feeding funnel by their specific gravity and utilized them for tube construction. This manner of tube construction is highly consistent with that of modern funnel-feeding polychaete worms.