Brachiopod pedicle traces: recognition of three separate types of trace and redefinition of Podichnus centrifugalis Bromley and Surlyk 1973

The rootlets or papillae of brachiopod pedicles that attach the animal to the substrate may dissolve calcareous substrates and leave an attachment scar or pedicle trace after death of the animal. This distinctive trace, which can be recognized back to the Palaeozoic, has been formally named Podichnus centrifugalis Bromley & Surlyk, 1973. The work described here shows that three different types of pedicle traces can be recognized and members of the two Terebratulide suborders, Terebratellidina and Terebratulidina, each appear to make a different type. Rhynchonellides may make all three types. These particular traces can be recognized as far back as the Mesozoic. As a result of this study the ichnogenus Podichnus and the ichnospecies P. centrifugalis are redefined, and two new ichnospecies, P. obliquus and P. perpendicularis , are introduced. The terms ‘colonist’ and ‘host’ are applied to an attaching brachiopod and its animal substrate respectively. In the New Zealand fossil record long-term colonist–host relationships can be traced from the Early Miocene to the Recent, based on the evidence of pedicle traces. In two examples, one or both animals evolve into new species whereas maintaining the colonist– host relationship.