An endemic community of Polish Late Ordovician gastropods

 

Authors: Dzik J

Article in press: Received 11 December 2024; Accepted in revised form 6 August 2025; Online 21 September 2025

Keywords: palaeobiogeography, Palaeozoic, phosphatization, molluscs, Bellerophontida, Jinonicella,

full text (PDF, 19.53 MB)

Export to RIS

 

Abstract

The Mójcza Limestone Formation exposed in the Holy Cross Mountains in southern Poland, being a part of the Małopolska microcontinent in the Ordovician, abounds in phosphate-coated originally calcareous fossils of microscopic size. Their geological age covers most of the Mid and Late Ordovician. The late Katian topmost bed of the Formation is especially rich in phosphatized larval and early postlarval gastropod conchs and yielded 8703 specimens taxonomically determinable at least at the genus rank. High-spired trochonematid conchs ornamented with delicate spiral striation between low ribs dominate the assemblage. Unlike other gastropod communities of similar age, this one was poor in bellerophontids and openly coiled platyceratids and despite the geographic proximity, the typically Baltic planispiral leseurillids are extremely rare. Comparable gastropod assemblages are unknown from the Perunica and Avalonia microcontinents or the continental Gondwana. Instead, specimens representing a few species of probable holopeids with smooth shell surface are abundant. Their conch geometry ranges from that already known among holopeids to the virtually planispiral, superficially resembling both, the coeval Baltic leseurillids and geologically younger euomphalids. Presumably, this taxonomic composition of the Mójcza gastropod community was a result of local speciation with a significant contribution from homoplasy to its taxonomic diversity.