The first documented co-occurrence of conodonts and graptolites in Silurian (Telychian) black shales of the Prague Synform, Czech Republic, and its stratigraphical and palaeoecological significance

The Želkovice locality, located in the south-western part of the Prague Synform, is well-known for its exceptionally well-preserved graptolites in black shales. Despite being studied repeatedly by several authors for over 170 years, no record of conodonts has been found until now. Both conodonts and graptolites are significant biostratigraphic groups of Paleozoic fossils. However, papers about their co-occurrence are rare. Their occurrence is tied to distinct lithofacies, which makes direct biozonal correlation difficult. Their partial overlap sheds new light on ecological niches, resilience, and the palaeoecological conditions of the environment. Determined conodonts belong to cosmopolitan taxa with a long range, inhabiting the deeper, distal parts of the shelf or continental slope. A total of 10 conodont species were identified at the same locality, spanning the entire linnaei Biozone. The occurrence of the index species Distomodus staurognathoides, whose stratigraphic range overlaps with the locally used graptolite linnaei Biozone and the internationally used guerichii Biozone, is documented. This study also documents rare specimens of pelagic fauna for the first time and discusses hypothetical parasitism and predation in conodonts and graptolites. This is the first study to describe the co-occurrence of both groups within the same lithology (black shale) and stratigraphic level, not only at the Želkovice site, but also elsewhere in the Silurian of the Prague Synform.