Abstract:Recently two new trilobite occurrences were discovered during geological mapping of fossiliferous shales of the Březina Formation around the village of Březina in the Moravian Karst (Czech Republic). The newly discovered localities are extraordinary because of the unexpected occurrence of articulated trilobite exoskeletons associated with brachiopods including supporting spines. The new atheloptic association of Mississippian trilobites is described for the first time from the Moravian Karst.

With over 15,000 extant species, Decapoda (or ten-legged crustaceans such as crabs, shrimp, lobsters, and relatives) are among the most speciose and economically important group of crustaceans. Despite of their diversity, anatomical disparity, and remarkable fossil record extending back to the Late Paleozoic, the origins of Decapoda and their phylogenetic relationships with eumalacostracans remains elusive and inconclusive. Molecular dating suggests that decapods originated in the Late Ordovician (~450 Mya), but no reliable fossil crown groups are found until the Late Devonian. Moreover, there is no consensus on which lineages belong to stem groups, obscuring our understanding of the roots of the ten-legged decapod body plans as a whole, and how they relate to other non-decapod crustaceans. We present new, exceptional fossils from the Late Devonian of Czech Republic and Poland that belong to Angustidontida, an odd shrimp-looking crustacean with a combination of anatomical features unlike those of any crown eumalacostracan known, extinct or extant. Our phylogenetic analyses, including representatives of all major lineages of crown eumalacostracans plus Angustidontida, identify angustidontids as the only known stem-group decapod, and give hints about the transformation series, polarity of change, and evolutionary pathways leading to the modern decapod body plans seen today.

Givetian limestones near Čelechovice contain rather abundant trilobites be longing to several species (for summary see Chlupáč 1992), whereas the Frasnian limestones of the Moravian Karst development are generally poor in trilobites and only a few rare specimens have been mentioned or described in the literature (

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