Taxonomic review of the ichnogenus Helminthopsis Heer 1877 with a statistical analysis of selected ichnospecies‐a discussion

In a recent paper Han and Pickerill (1995) evaluated the taxonomy of different ichnospecies of Helminthopsis HEER and based their revised taxonomy on a statistical analysis of the burrow course. The statistical analysis was carried out by a so-called Fourier Transfer (FT) analysis. FT analysis can only be performed (e.g. Bracewell, 1978) on uniquely determined functions. The course of many Helminthopsis burrows has bell-shaped elements, which means they are not uniquely determined in x (Fig. 1), and the burrow course needs to be transformed into a uniquely determined function which — literally —smooths out the bell-shaped elements. It is also a requirement that the backward transformation is uniquely determined; otherwise the same transformed function can result from different burrow courses (cf. Bracewell, 1978).