Ichnotaxonomic Review of Dendriniform Borings Attributed to Foraminiferans: Semidendrina igen. nov.

The taxonomy of trace fossils is essentially separated from that of the organisms that produce them as two independent systems: ichnotaxonomy and biotaxonomy. A distinctive group of borings, ranging in age from Ordovician to Recent, and having a rosetted plexus of galleries radiating in some from a main chamber, comprises an ichnofamily, named Dendrinidae in this chapter. A characteristic new member of this family, Semidendrina pulchra is introduced in the chapter. However, examination of numerous recent individuals failed to reveal any foraminiferans within the borings, and the nature of the tracemaker remains uncertain. The biological and ichnological nomenclatures are concerned with two entirely different taxobases and cannot be combined or confused. Biotaxonomy treats nomenclature of organisms, and ichnotaxonomy treats the structures produced by their activities. It is always desirable to attempt an identification of a tracemaker in the case of a trace fossil as distinctive as S. pulchra. X-radiography of similar borings from the recent seafloor had revealed two specimens containing a single foraminiferan within the main chamber of each boring. The foraminiferans were in such a position that it appeared likely that they had created the borings. Unexpectedly, careful examination of a large number of recent specimens of S. pulchra failed to reveal any foraminiferans. Nevertheless, the boring has a morphology that suggests a foraminiferal architect. As other tracemaker organisms (sponges, fungi, bacteria) can be discounted on the basis of morphology of the boring, the ascription remains uncertain even at phylum level. Further study of Recent S. pulchra may eventually reveal the responsible organism.