Can micromorph articulate brachiopods from the underwater caves in the Adriatic Sea give insight for the palaeoecology of Triassic and Jurassic faunas describe from Montenegro?

Palaeoecological reconstructions of Mesozoic brachiopods are mostly based on the work of Ager (1965, 1967) and Vörös (1986), who discussed their morphology, mode of occurrence, sedimentary setting and relationship with other organisms, as well as other characteristics they considered important. Additionally, Ager (1965, 1967) considered that the comparisons with recent brachiopod faunas are not entirely suitable for palaeoecological reconstructions, since fossil brachiopods represent a much more numerous and morphologically diverse group. Although this is true and extant brachiopods represent only a minor element in recent faunas, their occurrences can still be used to validate previously proposed reconstructions or propose new reconstructions. Comparison made in the present abstract is based on literature data, as well as our own field observations regarding the Triassic and Jurassic brachiopod faunas.
Mesozoic articulate brachiopod record of Montenegro is well known (Mirković & Mirković, 1995 for an overview). However, most of described faunas are known only from the Middle Triassic and Lower Jurassic sedimentary rocks. During these stages, facial diversification was very high in the External Dinarides, which led to formation of different macrofaunal fossil assemblages throughout. Brachiopods are usually preserved within mass occurrence beds, alone or with crinoids and/or bivalves, in clastics or carbonates. In several cases they occur in neptunian sill infillings. Such sills were formed together with neptunian dikes during phases of extension and are accompanied by the demise of shallow-water productions areas, i.e. carbonate ramps and platforms. In contrast, they are rather rare in all other sedimentological settings.
Unlike the fossil record, recent brachiopods are almost unknown from Montenegrin part of the Adriatic Sea (Gamulin-Brida, 1983), with only rare reports from other parts of the Adriatic as well (Logan et al., 2004 for an overview).
Extant articulate brachiopods that inhabit underwater caves in the Adriatic Sea, have not been used for comparison with fossil faunas so far. In total, six species have been registered within underwater caves in the Adriatic Sea: Argyrotheca cistellula, Argyrotheca cuneata, Joania cordata, Megathiris detruncata, Gwynia capsula and Tethyrhynchia mediterranea (Simon & Willems, 1999; Logan, 2003; Legac, 2012; Rosso et al., 2021). In the morphological sense, these species are well comparable with fossil representatives of Pelsonian and Sinemurian age, described from Montenegro. Pelsonian faunas described from neptunian sills (Bešić, 1945, 1949), recently also observed in Seljani (unpublished, ongoing research), contain several rhynchonellids and spiriferids which are morphologically very similar to recent species. Likewise, Sinemurian “Rhynchonellina” faunas (Eichenbaum, 1883; Bittner, 1895) are very similar to Argyrotheca cuneata, Tethyrhynchia mediterranea and Megathiris detruncata. They are found within sparitic recrystallized limestone, which Sandy et al. (2021) suggested to be the equivalent of Hierlatz Limestone (Vörös, 1991), partly formed as fissure fillings.
Whole fossil underwater caves are not likely to be preserved until today, leaving neptunian sills/dikes fillings as possible equivalents of such environments. It should also be noted that cited extant species from the underwater caves are all micromorph forms, most of them present in other environments as well (e.g. Albano & Stockinger, 2019). However, based on their compared morphologies, and the type of sedimentary rock in which fossil ones are found, it can be assumed that fossil and recent species could inhabited similar environments. Likewise, themode of preservation of fossil representatives suggests at least parautochthonous, if not even truly autochthonous assemblages. This is in accordance with the opinion given by Ager (1965) that unrelated species of articulate brachiopods evolved similar characteristics, in order to adapt to similar living environments.
The main aims of future investigations will be to try and register the underwater caves with brachiopod faunas in the Montenegrin part of Adriatic Sea and find as many localities as possible with Triassic and Jurassic brachiopod faunas in the neptunian sill fillings. Further ecological investigations of extant faunas, and taphonomical investigations of fossil assemblages, should provide enough data for detailed palaeoecological reconstructions.
Acknowledgements: Present abstract is a contribution to a national scientific project Triassic fossil faunas of Montenegro and recent faunas of the Adriatic Sea - reconstruction of life conditions in geological time through comparison