Megistaspis gibba from the Area of Mining Works in Mielenko Drawskie, the Drawskie Lakeland, Poland

The area of mining works in Mielenko Drawskie in the Drawskie Lakeland, Western Pomeranian Province, is a typical post-glacial site. However, marine sedimentary limestones of Swedish origin can be found here. These limestone rocks are characterised first of all by a large content of ferric oxide (III) (Fe2O3). Fossilised arthropods (Arthropoda) can be observed in them, in particular trilobites (Trilobita). It can be stated that the largest and most frequently encountered here trilobites of the Megistaspis genus are Megistaspis gibba. However, no complete specimens of these trilobites have been observed so far. In the territory of Poland, about 170 species within the group of Ordovician trilobites, belonging to 84 genera and represented by 36 families, have been known. Twenty one species are Polish holotypes. The Ordovician trilobites have not been examined to the same extent. The Upper Ordovician trilobites have been elaborated the best. About 80 species, belonging to 40 genera, have been found. The expansion of trilobites depends on the distribution of lithofacies within the Ordovician sedimentation basin. In limestone and marl lithofacies, trilobites are found accompanied by most abundant brachiopods, cephalopods, ostracods and echinoderms. Trilobites are found abundantly together with brachiopods in light, limestone clayey-mud sediments of the Upper Ordovician period in the Świętokrzyskie Mountains. Trilobites are of fundamental importance when elaborating the biostratigraphy of Ordovician sediments, in particular those developed on carbonate, marl and mud lithofacies. Starting with the Lower Arening period trilobites became abundant. The leading species of the Arening trilobites belong to Megistaspis, Symphysurus, Nileus, Metaptychopyge and Asaphus orders. Special attention should be paid to two species: Symphysurus angustatus (Sars et Boeck), a leading species for the Lower Arening period, and Megistaspis limbata (Boeck), both being broadly distributed geographically and delimiting the horizon within the Upper Arening period. Within the area of the aforesaid opencast mine (mining works in Mielenko Drawskie), one can find post-glacial Quaternary sediments, containing the fossils dated back to the period from the Cambrian to the Quaternary. However, the most abundant are limestone sediments with Ordovician trilobites.