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

The ichnogenus Helminthopsis Heer 1877 is a relatively simple, unbranched, horizontal, internally unstructured, pre‐ or post‐depositional burrow, or trail, that follows an irregularly sinuous or more commonly an irregularly winding or meandering course. The geometric variation in course, its most significant ichnotaxobase, is invariably complex and has resulted in considerable taxonomic disorder, particularly at the ichnospecific rank. This confusion is compounded by the fact that no diagnoses, and, or, detailed descriptions of several of its historically defined ichnospecies were provided and for other ichnospecies such considerations are ambiguous.

In view of these problems, the validity of the 21 previously described ichnospecies is reviewed and each taxonomically reassessed. We suggest that of these ichnospecies, H. regularte Crimes and Crossley 1991 is best regarded as a synonym of Cochlichnus anguineus Hitchcock 1858; H. irregularis (Schafhäutl 1851), H. antigua Sacco 1888 and H. curvala (Katto 1960) are synonyms of Helminthoida crassa Schafhäutl 1851; H. tunluensis Yang 1986 and H. yushuensis Yang 1986 are synonyms of Helminthoida miocenica Sacco 1886; H. akkesiensis (Minato and Suyama 1949) is a synonym of Helminthoida cf. miocenica; H. sinuosa Azpeitia Moros 1933 is a synonym of Cosmorhaphe sinuosa (Azpeitia Moros 1933); H. involuta Stefani 1895 and H. concentrica Azpeitia Moros 1933 are synonyms of Spirorhaphe involuta (Stefani 1895); H. horizontalis (Kern 1978) is a synonym of Phycosiphon incertum Fischer‐Ooster 1858; H. magna Heer 1877 and H. intermedia Heer 1877 are synonyms of Scolicia Quatrefages 1849, namely Scolicia plana Ksiażkiewicz 1970 or Scolicia prisca Quatrefages 1849 for the former and S. prisca the latter; H. barbeyana Stefani 1895 and H. labyrinthica Heer 1877 are. best considered nomina nulla and H. toyoensis Katto 1964 and H. sigmoideus Wang 1989 are nomina dubia.

Of the remaining 4 ichnospecies of Helminthopsis, H. granulata Ksiażkiewicz 1968 is easily and readily distinguished by its external granulate or tuberculate ornamentation. However, H. abeli Ksiażkiewicz 1977, H. hieroglyphica Heer in Maillard 1887 and H. tenuis Ksiażkiewicz 1968 cannot easily be differentiated. For these more problematic ichnospecies, a frequency component analysis using a FORTRAN program to perform a Fourier transform algorithm was applied in an attempt to statistically assess their validity or otherwise. The results suggest that H. tenuis is best considered a synonym of H. abeli, whereas H. hieroglyphica, although historically poorly defined, should still be regarded as a valid ichnospecies.

Thus, we believe that of the many ichnospecies previously assigned to Helminthopsis, only 3, namely H. abeli, H. granulata and H. hieroglyphica, can be regarded as taxonomically valid and useful forms. H. granulata is characterized by its external ornamentation and the precise nature of its irregular course is not an essential ichnotaxobase. H. abeli should be adopted for irregularly meandering Helminthopsis that do not exhibit straight segments and H. hieroglyphica for examples that possess straight segments interspersed with irregularly and variably developed sinuous segments but no horseshoe‐shaped segments. Synonymies of these three ichnospecies are included.

Key words:

• Helminthopsis
• invertebrate trace fossils
• taxonomy
• statistics