The paradoxical ichnotaxonomy of Thalassinoides paradoxicus: a name of different meanings

Thalassinoides paradoxicus (Woodward, 1830) is a prevalent and frequently reported ichnotaxon, but given its early erection and subsequent revisions, it now is poorly understood and lumps together three different kinds of trace fossils having distinct characteristics. A clear definition (i.e., diagnosis) of each individual component is crucial for ichnotaxonomic stability and the application of these ichnotaxa in environmental and evolutionary interpretations. Originally described and figured as the zoophyte Alcyonia (soft-bodied coral) from the Upper Greensand (Lower Cretaceous) of southern England over 200 years ago, it became the type of Spongia paradoxica Woodward, 1830. This type was mostly ignored by subsequent workers, and instead branched burrows from the Upper Cretaceous Chalk were regarded of being representative for S. paradoxica, a form that became typified with a neotype as Thalassinoides paradoxicus Kennedy, 1967. Furthermore, irregularly branched firm- to hardground burrows from the same strata were also called T. paradoxicus but rather belong to Balanoglossites triadicus Magdefrau, 1932. A taxonomic discussion of the involved ichnotaxa is presented, resulting in the erection of the new ichnogenus Lamellaecylindrica, including L. paradoxica (Woodward, 1830), and the differentiation of the ichnospecies Thalassinoides paradoxicus Kennedy, 1967 and Balanoglossites triadicus Magdefrau, 1932. Each of these ichnotaxa is a common constituent of a specific lithofacies and environment.