Anna Żylińska

Priapulid worms: Pioneer horizontal burrowers at the Precambrian-Cambrian boundary

The major evolutionary events that characterize the Precambrian–Cambrian transition are accompanied by profound ecological changes in the composition of benthic communities, the nature of the substrate, and the occupation of marine ecospace. The increased animal activity on and within the substrate is attested to by numerous trace fossils, such as the cosmopolitan Treptichnus pedum whose fi rst appearance is used as the global stratotype section and point (GSSP) to mark the base of the Cambrian. In spite of its major importance in biostratigraphy, the maker of Treptichnus trace fossils, and more generally of treptichnids, has long remained an enigma. Treptichnids were subhorizontal burrow systems produced in the subsurface and had a worldwide distribution throughout the Cambrian. Here we show, by using experimental ichnology, that the treptichnid burrow systems were most probably produced by priapulid worms or by worms that used the same locomotory mechanisms as the Recent priapulids (e.g., Priapulus). Their typical three-dimensional morphology with repeated arcuate probing branches suggests that their function was related to the feeding strategy of the worm such as predation or scavenging upon small epibenthic or endobenthic invertebrates. This interpretation is strongly supported by the preserved gut contents of Cambrian priapulids from the Burgess Shale Lagerstatte that contain effectively a variety of small epibenthic prey. The antiquity of treptichnids would designate priapulids as one of the earliest infaunal colonizers of the substrate that possibly interacted with epibenthic communities, thus playing a leading role (1) in the construction of the early marine food chain, and (2) as important subhorizontal bioturbators in the early stages of the “Cambrian Substrate Revolution.”

Global Cambrian trilobite palaeobiogeography assessed using parsimony analysis of endemicity

Abstract Palaeobiogeographical data on Cambrian trilobites obtained during the twentieth century are combined in this paper to evaluate palaeoceanographic links through c. 30 myr, once these arthropods biomineralized. Worldwide major tectonostratigraphic units are characterized at series intervals of Cambrian time and datasets of trilobite genera (629 for Cambrian Series 2, 965 for Cambrian Series 3, and 866 for the Furongian Series) are analysed using parsimony analysis of endemicity. Special attention is given to the biogeographical observations made in microcontinents and exotic terranes. The same is done for platform-basinal transects of well-known continental margins. The parsimony analysis of endemicity analysis resulted in distinct palaeogeographical area groupings among the tectonostratigraphic units. With these groupings, several palaeobiogeographical units are distinguished, which do not necessarily fit the previously proposed biogeographical realms and provinces. Their development and spatial distributions are broadly controlled by Cambrian palaeoclimates, palaeogeographical conditions (e.g. carbonate productivity and anoxic conditions) and ocean current circulation. Supplementary material: Global dataset of Cambrian Epoch 2 (A), Cambrian Epoch 3 (B) and the Furongian Epoch (C) trilobite genera are provided at: http://www.geolsoc.org.uk/SUP18669

Application of morphometric techniques for taxonomic revision of Berabichia oratrix (Orłowski, 1985) (Trilobita, Cambrian) from the Holy Cross Mountains, Poland

ABSTRACT Detailed analysis of c. 900 trilobite specimens from the Cambrian Series 2 of the Holy Cross Mountains in Poland, assigned hitherto to Comluella oratrix Orłowski, 1985 and Comluella igrzycznae Orłowski, 1985, has shown that the two species constitute in fact a monospecific assemblage representing Berabichia oratrix (Orłowski, 1985). The differences pointed out in the original diagnoses are obviously caused by taphonomic processes. To test the hypothesis of a monospecific assemblage, six sagittal and exsagittal and five transverse parameters were measured and calculated for 182 best-preserved cranidia; from this dataset, 121 cranidia with the complete set of measurements were subjected to bivariate and multivariate morphometric analyses and discriminant analysis. Results of the morphometric analysis point to the significant role of tectonic deformation in the variation of the studied sample that could have led Orłowski (1985) to distinguish two separate species. Application of graphic techniques on photographs of distorted specimens lying in different directions with regard to the stress field allowed to obtain specimens statistically indistinguishable in terms of their sagittal and transverse proportions, thus confirming the tectonic overprint on the morphology of the analyzed trilobite sample.

Very large acritarchs from the Furongian (upper Cambrian) rocks of the Holy Cross Mountains, central Poland

ABSTRACT Various authors have described and illustrated exceptionally large acritarchs from the Furongian (upper Cambrian) from different parts of the world. The different morphotypes clearly belong to the ‘diacromorph’ acritarchs, but have until now usually been attributed, tentatively or erroneously, to the genus Veryhachium. Based on new material from the Holy Cross Mountains (central Poland) and the literature, the new genus Gigadiacrodium is erected to include these stratigraphically diagnostic and easily distinguishable morphotypes. The new genus includes the following species: Gigadiacrodium martinae (Pittau 1985) comb. nov., emend. nov. (type species) and Gigadiacrodium vidalii sp. nov. In addition, a new combination is proposed: ?Solisphaeridium mutabile Di Milia et al. 1989, comb. nov.