Ichnology and palaeobiology of Phoebichnus trochoides and Schaubcylindrichnus heberti comb. nov.

The three-dimensional reconstructions of Phoebichnus trochoides and Schaubcylindrichnus (Palaeophycus) heberti created as part of this thesis allow us to fully understand and characterize the three-dimensional morphology and palaeobiology of these common taxa. Three-dimensional reconstructions demonstrate that P. trochoides is a large stellate burrow composed of numerous long galleries produced by a deposit feeding organism. This study reports for the first time that the central zone is composed of stacked disk-shaped layers of highly bioturbated sediment, the radial burrows are composed of a sand-rich lining of pelleted annuli surrounding an active sand-rich fill, and the presence of subtle conical features above the radial galleries that are inferred to result from collapse cone feeding. Reconstructions of heberti demonstrate that the thick walled burrows are composed of sand-rich annular rings, are a broad U-shape, and may be either clustered or isolated. Our observations show that the morphology of heberti is inconsistent with the generic diagnosis of Palaeophycus, but is morphologically comparable to Schaubcylindrichnus, and is herein synonymised with Schaubcylindrichnus to create S. heberti comb. nov. The three-dimensional reconstructions have revealed a number of hitherto unknown morphological elements to both taxa which has facilitated new interpretations of the trace-makers behaviour. The data improves the taxonomic understanding of both P. trochoides and S. heberti which require significant taxonomic change and emendation of diagnoses at the species and genus level.