Otoliths in situ from Sarmatian (Middle Miocene) fishes of the Paratethys. Preface: a first attempt to fill the gap between the otolith and skeletal records of teleost fishes

Abstract

The studies presented in this special issue describe and evaluate otoliths in situ in 18 species of extinct Paratethyan fishes, 17 from Sarmatian, and one from Karaganian deposits. Together with previously described fishes from the area with otoliths in situ and additional works which we are aware of being in progress, this time interval has now yielded 34 fish species with otoliths in situ, approximately equivalent to one-third of the entire Sarmatian fish fauna of the Paratethys known to date. Therefore, it represents by far the most diverse fossil fish fauna with otoliths in situ. The implications of the linking of skeletal and otolith data are briefly discussed as well as the prospects for future research. The anecdotal history of the formation of the work group which became engaged in these studies is presented.

Articulated fish skeletons with otoliths in situ are the necessary ingredients to link these two data sets which have been traditionally treated separately. The link is generally considered to be rare and occasional. This was also our idea, when a few years ago, we exchanged our views about a long forgotten gadid fish originally described from the Badenian of Austria by Kner in 1862—Palimphemus anceps. Giorgio Carnevale at that time reappraised Palimphemus anceps in cooperation with Mathias Harzhauser and Ortwin Schultz (Carnevale et al. 2012). Werner Schwarzhans recalled of an articulated gadid fish specimen kept at the Wrocław University in Poland with an otolith in situ. A detailed analysis of this articulated skeleton revealed that it also represents Palimphemus anceps. Even more exciting, it helped to synonymize the otolith-based species Colliolus sculptus (Koken 1891) with the skeleton-based Palimphemus anceps Kner 1862, thereby eradicating a case of more than 100 years of parallel taxonomy (Schwarzhans 2014). This result inspired us to look for additional cases allowing the correlation between skeleton- and otolith-based taxonomy, which we both feel is absolutely necessary. Our attention then became attracted by comments found in Schubert (1906) about otoliths in situ he had seen in ten different species of articulated skeletons from the collection of Sarmatian fishes from Dolje near Zagreb, Croatia assembled by Dragutin Kramberger. Katarina Bradić contacted Werner to discuss the identity of certain otoliths found in the vicinity of Belgrade, Serbia (Schwarzhans et al. 2015). This in turn led to approach Sanja Japundžić in Zagreb, Croatia, where most of the Karmberger’s specimens are kept in the collection of the Croatian Natural History Museum (CNHM). Katarina Bradić also informed us that she had identified a number of fishes with otoliths in situ in the collection assembled and studied by Jelena S. Anđelković from the Sarmatian of Belgrade housed at the Chair of Historical Geology, Department of Regional Geology, Faculty of Mining and Geology, and University of Belgrade (RGF). Werner Schwarzhans traveled to Zagreb to meet Sanja Japundžić and examine the Kramberger’s fishes, and to Belgrade to meet Katarina Bradić and see the Anđelković material. The amount of data was overwhelming and the quartet agreed to realize a series of contributions dealing with the Sarmatian fishes with otoliths in situ from those two collections (Schwarzhans et al. 2017a, b, c, d, e). During the preparation of the various articles, further colleagues were invited to participate: Alexandre F. Bannikov, who made available specimens of Atherina suchovi with otoliths in situ from the Sarmatian of Moldavia (Schwarzhans et al. 2017a), Andriy Bratishko for his expertise in otoliths from the Miocene of the Eastern Paratethys (Bratishko et al. 2015, and Schwarzhans et al. 2017b, c) and Harald Ahnelt for his expertise in gobies of the Ponto-Caspian Basin (Schwarzhans et al. 2017c). During a trip to Moscow in the same year, Werner met with Eugenia Baykina, who was reviewing the fossil clupeids from the Paratethys. She found two clupeid species containing otoliths in situ among her material and it was decided to separately describe them (Baykina and Schwarzhans 2017a, b). The scope and format were agreed by the group when the editor of the Swiss Journal of Palaeontology proposed to publish these articles in a special issue of the journal dealing with otoliths in situ.

The initial concept was to focus on the otoliths in situ and their correlation with isolated otoliths, with a limited revisionary work of articulated skeletons (Schwarzhans et al. 2017a). However, most of the fishes formerly studied by Kramberger and Anđelković have never been reviewed and it was soon recognized that our concept was unsatisfying. For instance, we found that the number of nominal species of the Gadidae, Lotidae, and probably also Clupeidae was exaggerated, while a single species of the Gobiidae described by Kramberger turned out to represent five different species belonging to five different genera, and finally, we identified the first fossil record of the family Gobiesocidae. Seventeen species of Sarmatian fishes and one from the Karaganian were found to contain otoliths in situ. Eleven of those are also known from isolated otoliths, including eight otolith-based species as junior synonyms. Two species—Sparus insignis (Prochazka 1893) (in Brzobohaty 1979) and Economidichthys triangularis (Weiler 1943) (in Schwarzhans et al. 2017c)—were first established by means of otoliths. Seven additional Sarmatian fish species have been previously described with otoliths in situ as well as three additional taxa from the Karaganian and Konkian. Furthermore, we are aware of studies currently under way by Giorgio Carnevale and Alexandre F. Bannikov (see Carnevale et al. 2006) and by Christoph Gierl and Bettina Reichenbacher (see Gierl and Reichenbacher 2015) containing at least six further Sarmatian fish species with otoliths in situ.

Overall, up to 30 Sarmatian or, more generally, 34 Middle Miocene fish species with otoliths in situ are now recognized from the Central and Eastern Paratethys (Table 1). These data clearly indicate that this represents by far the most diverse fossil fish fauna with linked skeletons and otoliths known to date (Fig. 1). About one-third of all the valid Sarmatian fish species are now recorded with otoliths in situ. Carnevale et al. (2006) and Bannikov (2010) noted that fishes from the Sarmatian of Russia and Moldavia often contain otoliths in situ. A similar pattern is also evident for the fishes from Dolje in Croatia and Belgrade in Serbia.

Table 1 List of Sarmatian and Karaganian/Konkian species with otoliths in situ, including a list of reviewed skeleton-based species and a list containing reviewed isolated otolith-based species

Fig. 1

Cenozoic chronological correlation chart of teleost diversity as based on articulated skeletons and otoliths, and number of species described with otoliths in situ. Scale bars in skeleton-based record: Black minimum count as based on Bannikov (2010) (Cenozoic of the CIS); Fierstine et al. (2012) (Cenozoic of California); Friedman et al. (2015) (London Clay); and Carnevale et al. (2014) (Monte Bolca) and various authors for the Miocene of Italy and Algeria. Grey best estimate count. Scale bars in otolith record: Black minimum count as based on Nolf, (2013). Grey best estimate count, including post 2013 data and estimation by one of us (WS). Scale bars in otoliths in situ record: Blue published, Red this volume, and Yellow currently under study

The articles presented in this special issue document the power of coherent integrated data that result from such investigations. First and foremost, the study of isolated otoliths is significantly enhanced by the link with skeletal material. Articulated fish skeletons offer a relevant amount of characters for systematic and phylogenetic analyses compared to otoliths, and therefore, otoliths in situ are essential for calibrating isolated otolith finds in the sedimentary record. This becomes ever more important for ancient geological times when allocation of isolated otoliths becomes increasingly ambiguous. Such calibration points will also help to better interpret non-linked otolith-based species. On the other hand, otoliths in situ also aid in the assessment of skeletal finds by offering valuable additional taxonomic information, as, for instance, shown here in the articles dealing with clupeids, gobies, and soleids. Furthermore, isolated otoliths are generally so much more common in the fossil record than identifiable articulated skeletons that they considerably enhance the understanding of the distribution of fossil fishes in space and time. Finally, we have also demonstrated that skeletal fish remains and isolated otoliths do not strictly duplicate and that in addition to many instances of a good correlation, there are also instances, where they complement each other.

Our experience with the otoliths in situ in Sarmatian fishes of the Paratethys convinced us that otoliths in situ may prove not to be as rare as often believed. We hope that the studies presented here will inspire many colleagues to look out for more of these cases and undertake many more studies that link the taxonomy of fossil articulated skeletal remains and otoliths.