What question did this study set out to answer?

This study aims to analyze the late Bajocian fossil assemblage and its bathyal environment in Komló, Hungary.

May 9, 2026Open Access

Small-sized, cephalopod-dominated fauna witnessing the late Bajocian transgression event and its bathyal palaeoenvironment from Komló, Mecsek Mountains (South Hungary)

LBLászló BujtorEszterhazy Karoly Catholic University THTamás HennKomatsu (Japan)LKLászló Kanizsai

Key Points

This study aims to analyze the late Bajocian fossil assemblage and its bathyal environment in Komló, Hungary.
Collection of a moderately preserved fossil assemblage from a calcareous marl section.
Statistical analysis of size distribution of phylloceratid specimens and Nannolytoceras to assess dwarfism.
Faunal comparison with northern Tethyan and Balearic Islands assemblages.
Fossil assemblage consists of 302 specimens with 20 genera and 11 species, dominated by Ammonoidea (78%).
Phylloceratid ammonites exhibit a Gaussian size distribution with a mean diameter of 24.5 mm.
Nannolytoceras specimens show a mean whorl height 43% smaller than contemporaneous assemblages from France.

Abstract

Abstract In the suburban area of Komló city (Mecsek Mountains, South Hungary), a moderately preserved fossil assemblage was collected from a calcareous marl section. The fauna is dominated by phylloceratid (50%) and lytoceratid (39%) ammonites among which Oppelia subradiata , Planisphinctes ( Lobosphinctes ) sp., Vermisphinctes ( Stomphosphinctes ) stomphus, and Dimorphinites dimorphus are first records from the Mecsek Mountains. Additional faunal elements are aptychi: Lamellaptychus sp. juv.; belemnites: Pachybelemnopsis sp.; bivalves: Bositra buchii , and other taxa, brachiopods: Apringia coarctata ; crinoids: Balanocrinus inornatus ; and diverse hexactinellid sponges. The fauna indicates the uppermost Bajocian Parkinsonia parkinsoni Zone (Bomfordi Subzone), which is in line with the lithostratigraphic subdivision of the region. The 302 specimens revealed a bathypelagic assemblage with a water depth exceeding 200 m and belong to 20 genera and 11 species dominated by Ammonoidea (78%). The sea floor was a muddy and well-oxygenated, vivid environment with infauna (burrowing bivalves) and epifauna (bivalves, crinoids and sponges). Epibionts ( Cementula spirolinites , Meandropolydora ? isp., and Entobia isp.) are detected on lytoceratid and perisphinctid specimens. The assemblage shows similarities to the sponge, ammonite and crinoid faunas of the northern Tethyan margin. The ammonite fauna consists of small-sized individuals. Size distribution of phylloceratid specimens revealed a Gaussian distribution with a mean diameter of 24.5 mm, referring to a similar environment reported from the upper Bajocian of Portugal. Statistical analysis of Nannolytoceras specimens also refers to a certain dwarfism: the mean whorl height of the present nannolytoceratid assemblage is 43% smaller than that of the contemporaneous French assemblage. The ammonite fauna shows the closest similarity to the uppermost Bajocian fauna of the Balearic Islands and portrays the uppermost Bajocian sea level rise event, when phylloceratid ammonites invaded the new, shallow marine environments where they did not find their optimal ecological conditions and remained small-sized.

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