The first occurrence of the earliest species of Acadoparadoxides outside West Gondwana (Cambrian; Holy Cross Mountains, Poland)

Abstract

Two hundred and eighty specimens of paradoxidids from two localities in the Holy Cross Mountains (Poland) have been reanalysed using morphometric techniques. Revision of the dataset provided evidence for the presence of two endemic taxa: Acadoparadoxides kozlowskii (Orłowski, 1959) and Acadoparadoxides samsonowiczi (Orłowski, 1959), both belonging to the earliest group of Acadoparadoxides, initially considered to be present only in Gondwanan successions. Thus, this is the first description of the members of this group outside West Gondwana. The taxonomic revision, and the presence of representatives of the earliest acadoparadoxidines coupled with the absence of taxa typical of Scandinavia that were previously described from this locality have resulted in the modification of the biostratigraphic scheme hitherto used in the Holy Cross Mountains. The newly established A. samsonowiczi – A. kozlowskii Assemblage Zone is correlated with the Morocconus notabilis Zone of Morocco, and thus represents the Cambrian Series 2 and 3 boundary interval. Links with West Gondwana challenge the existing palaeogeographic interpretations for the southern part of the Holy Cross Mountains and point to an urgent need to revise the position of the Małopolska Block during the middle Cambrian.

Comment on: Álvaro, J. J., Esteve, J. & Zamora, S. 2019. Morphological assessment of the earliest paradoxidid trilobites (Cambrian Series 3) from Morocco and Spain [Geological Magazine]

“…First of all, not taking tectonic deformation into account may be risky: although in classic morphometrics the amount of deformation present in the sample may be negligible, geometric morphometrics is more vulnerable to such distortion. In a recent study, Nowicki & Żylińska (2018) have tested the utility of geometric morphometric analyses on species of Acadoparadoxides from lowermost middle Cambrian strata of the Holy Cross Mountains, Poland. Nowicki & Żylińska (2018) noted a study by Angielczyk & Sheets (2007), which concluded a comprehensive validation of numerical retrodeformation techniques in geometric morphometrics.…”

“…According to the results of Nowicki & Żylińska (2018), the removal of a principal component that is best correlated with the length:width proportions does not improve the outcome when the axial symmetry is not restored in the specimens before the procedure. A procedure known as symmetrization improves the results, but can be safely applied only to specimens in which the deformation is relatively simple, without a high amount of noise added to the deformation, which would compromise the apparent significance of those analyses.…”

“…It does indicate rather that the applied technique was not able to detect potential differences. As recently emphasized by Nowicki & Żylińska (2018), not rejecting the null hypothesis in such studies cannot be taken as their confirmation, particularly as the analysis in Álvaro et al (2018) suffers from several problems presented above that undermine its results. In contrast, morphological differences have been described in Geyer & Vincent (2015) in a classic way, but these were not discussed in any detail in Álvaro et al (2018).…”

“…Such selection results in an artificial transition of the landmark position variance from the marginal landmarks/semilandmarks to the axial ones. In a set affected by deformation, this problem may be essential (Nowicki & Żylińska, 2018). In addition, the landmark analyses do not reflect differences in the dorsoventral component (relief), which for example serves to indisputably discriminate the pygidia of A. pampalius from similar pygidia of A. levisettii or A. ovatopyge.…”

A new look at Eccaparadoxides (Cambrian, Trilobita) and its biostratigraphic significance

“…In addition, the Polish specimens seem to have an older occurrence in the Holy Cross Mountains than those from the type area in southern Sweden (Żylińska and Szczepanik 2009). These specimens have been recently reassigned to the endemic species Acadoparadoxides kozlowskii (Orłowski, 1959a) and bear no resemblance to Eccaparadoxides (Nowicki and Żylińska 2019). Westergård, 1936), known from Öland and Jämtland in Sweden, from the Oslo district in southern Norway, and from the Peribaltic Depression in northern Poland, is usually regarded as a species of Acadoparadoxides.…”