Callovian corals from the Swiss Jura

Twelve solitary and platy, colonial coral taxa assigned to the families Microsolenidae, Misistellidae, Montlivaltiidae, Rayasmiliidae, and Thamnasteriidae are described and illustrated from the Callovian (Ifenthal Formation, Herznach Member) of the area of Andil near Liesberg, about 20 km WSW of the town of Basel, Switzerland. The platy growth forms and the presence of five species of the superfamily Cyclolitoidea suggests that these corals lived under low-level light conditions.


Introduction
The Mesozoic rocks forming the Jura Mountains in NW Switzerland were deposited in an epicontinental setting.The Jurassic rocks accumulated under shallow-marine conditions and consist principally of limestone, marl, and mudrock.Due to differential subsidence and relative changes in sea level, the domain of the Swiss Jura Mountains became morphologically diversified and, accordingly, so did the depositional regime and related faunal associations.Partly, these deposits are very rich in fossils and their intensive investigation began in the nineteenth century through, for instance, Agassiz (1839Agassiz ( , 1840) ) and Koby (1880Koby ( -1889)).
During the Middle and Late Jurassic, carbonate platforms developed in the domain of the Swiss Jura Mountains, housing local coral patches or even chains of patch reefs.For the Middle Jurassic (Bajocian), shallow and isolated coral meadows were reported, such as, for instance, from the Gisli-Fluh (Gonzalez, 1993;Gonzalez & Wetzel, 1996).Very prominent coral occurrences are described from the Late Jurassic (Oxfordian; Gygi, 2000;Gygi & Persoz, 1986).Starting with the coral meadows during the early Middle Oxfordian (Liesberg Member of the Bärschwil Fm.), locally, reefs developed further up during the Middle Oxfordian St. Ursanne Formation.These corals were taxonomically investigated, first by Thurmann and Etallon (1864), then by Koby (1880Koby ( -1889)), and later by Beauvais (1963), and Birenheide (1969).The material studied by these authors originated mainly from the Middle Oxfordian in the areas of Combe Chavatte, La Caquerelle, Saint-Ursanne, among others.In contrast, Middle Jurassic corals, late Bajocian to early Bathonian in age, from northern Switzerland, have only be reported (Gonzalez & Wetzel, 1996), but are not yet taxonomically dealt with in detail, except for the studies of Meyer (1888), Koechlin (1933Koechlin ( , 1950)), Beauvais (1966), and Kutz et al. (2020).The present study addresses a small coral fauna from the Callovian of Liesberg (Kanton Basellandschaft; Fig. 1) that has been reported for the first time by Gründel and Hostettler (2012).

Geological setting
In NW Switzerland, the deposits of the Swiss Jura Mountains are built-up by Mesozoic rocks deposited in the southern part of the Mesozoic Central European Basin System, which was mainly covered by an intracontinental epeiric sea that became connected to the Tethys in the South during the Middle Jurassic (e.g., Maystrenko et al., 2008;Ziegler, 1990).During the Middle and Late Jurassic, the rocks forming the Swiss Jura Mountains record the changing morphology of the depositional realm (Allenbach & Wetzel, 2006;Burkhalter, 1996;Pieñkowski et al., 2008;Wetzel & Allia, 2000) that appears to have been considerably affected by pre-existing tectonic structures in the basement, which became temporarily re-activated (e.g., Wetzel et al., 2003).
The basement in central Europe was tectonically structured towards the end of the Variscan orogeny during the late Palaeozoic, when numerous basins, grabens, half-grabens, and fault systems formed (Arthaud & Matte, 1977;Boigk & Schöneich, 1974;Ménard & Molnar, 1988;von Raumer, 1998).In the study area and its surroundings, such tectonic structures in the basement were identified on seismic records (Madritsch et al., 2018;McCann et al., 2006;NAGRA, 2008).During the Triassic, peneplanation took place, and continental and restricted marine deposits accumulated, including up to 100-m-thick evaporites.At the beginning of the Jurassic, a major transgression occurred, and mainly fully marine rocks accumulated since then (Fig. 2).
When the Tethys Ocean to the south and the North Atlantic Ocean to the west opened during the Jurassic, the area in between was affected by extensional and transtensional stresses (e.g., Faerseth, 1996;Philippe et al., 1996).Even short-term changes in the stress field might have occurred (Robin et al., 1998;Wetzel et al., 2003).Pre-existing basement structures became temporarily reactivated, as evidenced by vein mineralisation data, changes in lithofacies and rock thickness across and adjacent to basement faults, and in particular, thickness anomalies exceeding depositional water depth, which imply synsedimentary differential tectonic movements (e.g., Wetzel et al., 2003;Timar-Geng et al., 2006;Brockamp et al., 2011;Reisdorf & Wetzel, 2018).Vertical movements in the basement, however, were dissipated by Triassic salt and, thus, the deposits above deformed mainly flexurally, and the basin floor was morphologically differentiated into gentle swells and depressions (e.g., Wetzel & Meyer, 2006;Wetzel et al., 2003).Differential subsidence has been deciphered, especially for the Middle and Upper Jurassic, including the up to 100-m-thick oolites and shallow-water carbonates of the Hauptrogenstein Formation (Gonzalez & Wetzel, 1996), the Passwang Formation below (Burkhalter, 1996), and the Callovian Ifenthal Formation above (Bitterli-Dreher, 2012), as well as Oxfordian formations (e.g., Allenbach, 2001;Wetzel et al., 2003;Fig. 2).Shallow-water sedimentation continued until the Upper Jurassic-Lower Cretaceous, constituting a rock pile less than 1 km thick (NAGRA, 2002).
The investigated material was collected from Callovian deposits that are exposed in the now abandoned ' Andil' clay pit near Liesberg, which is about 20 km WSW of the town of Basel (Swiss coordinates 2′598′686/1′250′087, Fig. 1).The corals were found in the Herznach Member of the Ifenthal Formation (Figs. 2, 3).In northern Switzerland, the Callovian represented a period of slow, but nonetheless differential subsidence, structuring the seafloor into gentle depressions and swells, the latter being temporarily exposed to wave influence, resulting in rock reworking, omission, and/or condensation (e.g., Bitterli-Dreher, 2012).Hence, the approximately 1-m-thick Herznach Member encompasses iron-oolithic marly limestone and marls that accumulated during a relative sea-level rise.Stratigraphically, these deposits belong to the Calloviense to Lamberti Zones (Hostettler, 2014; Fig. 3).The stratigraphically lowest iron-oolithic bed was named 'iron-oolithic lumachelle bank' by Stäuble (1959), because of its richness in bivalve shells.It was included into the Herznach Member by Hostettler (2014).According to ammonite finds, it belongs to the Enodatum Subzone (Calloviense Zone), and it also contains the corals described here.In addition to the outcrop locality Andil, the Herznach Member is locally exposed from the Col de la Croix in the north to the Grenchenberg in the south, and from Liesberg village in the east to the marginal area of the Franches-Montagnes in the west (Fig. 1).The fossil-bearing Callovian deposits are only exposed in river beds, clay pits, or during temporal excavations.
The corals were collected from only one interval consisting of an iron-ooid-bearing, clayey limestone, which was deposited on top of a well-developed hardground in the lowermost part of the Herznach Member (see Fig. 3).The coral-bearing interval contains numerous shells of various bivalves; most common are specimens of the genera Plagiostoma, Ctenostreon, Chlamys, Trigonia, Orthotrigonia, Protocardia, Pseudotrapezium, and non-identified members of the family Arcidae.Fragments of tree-shaped bryozoan colonies and crinoids of the genus Millericrinus are also common.Ammonites are quite rare.The fauna is allochthonous and the corals are quite randomly dispersed in the rocks, and do not occur directly on the hardground, except for one juvenile single coral that was found attached to the hardground.Occasionally, the corals grew on thick-shelled bivalves.The coral colonies are generally flat, do not exceed ten centimetres in their largest lateral dimension, and are not higher than two centimetres.They are bored and, partly only preserved as fragments.The surrounding rock could not be completely removed from the corals and, therefore, the surface of the corals is not observable.

Methods
Coral specimens were collected from one stratigraphic horizon.After careful cleaning, they were cut and polished.Thin sections in both transversal and longitudinal orientations were prepared, whenever possible.Thin sections were scanned in plane light by using a flatbed scanner with an optical resolution of 6400 dpi.Scanned images were then transferred to greyscale bitmaps.Their quality was amended by histogram contrast manipulation (contrast stretching), whenever possible.
To gain more insights into the intraspecific variation of these corals, and to obtain a better strategy for comparing species, the corallite dimensions, and number of septa or septal density were systematically measured using the scanned thin sections.To achieve statistical significance, the largest possible number of measurements was taken.This number was mainly determined by the size and quality of the thin sections, and the size of the single corallites in relation to the size of the thin sections.For each type of measurement (such as the corallite diameter or number of septa), the following values were obtained: n number of measurements.min-max lowest and highest measured values.µ arithmetic mean (average).s standard deviation.cv coefficient of variation according to K. Pearson.µ ± s first interval.
Thin sections were measured and values were calculated using the Palaeontological Database System PaleoTax, module PaleoTax/Measure (https:// www.paleo tax.de/ measu re).Previous studies (for instance Löser, 2012Löser, , 2020) ) have shown that the corallite dimensions (septal counts, or septal density) have a certain range throughout the whole coral colony.The comparison of morphometric data may serve as a method to distinguish fossil coral species.
The morphometric data obtained from the corals of the study area were compared with the morphometric data of available specimens in worldwide collections of Jurassic and Cretaceous corals.The described and illustrated coral specimens are part of the Fondation paléontologique jurassienne (FPJ), Glovelier, Switzerland, and they are kept at the Natural History Museum Bern, Switzerland.
The distribution data (as reflected in the synonymy lists) are almost entirely based on examined material.Material that is only mentioned in the literature and material that is not available or is insufficiently described and illustrated in the literature were not taken into account.To obtain better insight into the distribution patterns of the present coral fauna, additional unpublished material has been included.This material is indicated by a collection acronym and sample number under 'Other material' .

Systematic description
Order Scleractinia Bourne, 1900 The classification of the order Scleractinia follows the studies by Vaughan and Wells (1943), Wells (1956), and Alloiteau (1952, 1957) with the difference that, instead of suborders, superfamilies are applied.More explication and comparison of both classification systems are found in Löser (2016) and Löser et al. (2018).

Superfamily Cyclolitoidea Milne Edwards & Haime, 1849
Family Microsolenidae Koby, 1889Dimorpharaea Fromentel, 1861 Type species.Microsolena koechlini Milne Edwards, 1860 Remarks.The type material of the type species is not available.According to the author of the genus, Fromentel (1861), the genus has the same structure as Microsolena Lamouroux, 1821 but differs by the presence of a central corallite and subsequent corallites that are arranged in rows.Pandey et al. (1999) contribute to the knowledge of the genus.Dimorpharaea williamsonensis (Wells, 1944)    This species was originally described from the Upper Oxfordian of Champlitten (France, Haute-Saône).The present specimen also compares to T. tourtiensis (Bölsche, 1871) but that species has much smaller corallite dimensions.
Clausastrea sp.Fig. 7 ilière, 1989;Löser, 2000).It seemed to be always easier to establish a new species in place to compare own material to the vast number of existing taxa (Lathuilière, 1988).
A correct taxonomic comparison is therefore difficult and must restrict to species where the type material was available for study.

Discussion
The overall environmental conditions for the corals were not optimal because they rarely occur in the Herznach Member.The studied corals are represented by large solitary forms or massive platy colonies.Platy corals are considered to be an adaptation to low-level light conditions, because of either water depth or turbidity (Kolodziej & Bucur, 2020;Rosen et al., 2002;and literature cited therein).Five out of the eleven species belong to the superfamily Cyclolitoidea.This superfamily is characterised by having balcony-like septal ornamentation (pennulae).These pennulae are considered to support a heterotroph form of alimentation (Löser & Bilotte, 2017;Schlichter, 1991) being, therefore, better adapted to low-level light conditions.Comparable associations from the Cretaceous consist predominantly of members of the superfamily Cyclolitoidea (Löser & Bilotte, 2017;Löser & Callapez, 2022).
The fauna consists of twelve species in seven genera.This number is too low to allow any palaeobiogeographic analysis.The seven coral genera are already known from the Callovian, except for Miscellosmilia, that was hitherto only known from the Kimmeridgian onwards (Fig. 8).All genera reach into the Cretaceous, but only two occur beyond the Cenomanian.The distribution of species (Fig. 9) suggests that most species have their first occurrence in the study area, but the data available for these Middle Jurassic corals is too scarce to confirm this pattern with certainty.The distinction of species is here based on morphometric data that have a certain statistical significance (see Löser, 2020), achieved by systematic measurements in colonial corals.Such data are hardly available from the literature.Therefore, a comparison based on the literature alone is difficult.When not taking into account the occurrences in the Cretaceous, the coral species from the present fauna are also found in Middle to Upper Jurassic coral faunas of the Czech Republic (Moravia), England (Wiltshire), Germany (Bayern, Niedersachsen, Württemberg), Japan (Wakayama), Poland (Swietokrzyskie), Romania (Tulcea), and Spain (Aragón, Valencia).

Fig. 1
Fig. 1 Location map, study area.Outcrop area marked by red asterisk

Fig. 2
Fig. 2 Schematic stratigraphic column of the rocks in northern Switzerland

Fig. 8
Fig. 8 Stratigraphical ranges of the genera of the study area.The blue bar indicates the age of the study area Wells, 1944onnected to each other, but in places connected to the columella.Septal lateral face with pennulae.Pali absent.Synapticulae not very common, mainly in the space between the corallites.Columella styliform, but very small.Endotheca with few thin tabulae.Budding intracalicinal, polystomodeal and complete.RemarksThe present specimen cannot be compared to available type data.It compares to the Early Cretaceous D. williamsonensisWells, 1944, but still has a lower number of septa.Morphometric data for D. williamsonensisWells, 1944, as obtained from the holotype NMNH M-547426, are as follows: crd, 3.2-3.8;septa 16-26.These values are minimum-maximum values because the thin section from the holotype is very small and yielded only a few values.
Description Thamnasterioid colony with corallites arranged in irregular rows.Septa regularly perforated.Microstructure of large trabeculae.Septa in cross section equal in thickness throughout the whole septum.No septal symmetry or generations.Septa not connected to each other, but some may be connected to the columella.Septal lateral face with pennulae.Pali absent.Costae present, confluent.Synapticulae not very common, mainly in the space between the corallites.Columella styliform and rather large.Endotheca absent.Budding intracalicinal, polystomodeal and complete.RemarksThe present specimen compares well in the distance between corallite rows and the septal counts to the (only illustrated) syntype of Microsolena ornataKoby, 1887 (MGL GEOLREG 4044).Dimorphastrea deickei Bölsche, 1877, Thamnasteria fromenteli Tomes, 1878, and Microsolena roemeri Bölsche, 1866 have comparable dimensions but much higher septal counts.ber of septa: crd 11-12; cdw, 6; septa, 26-30.These values are minimum-maximum values because the thin section is very small and yielded only a few values.Other material BSPG 2003 XX 5489 (Lower Aptian from Greece, Viotía, Arachova).Other occurrences Aptian of the Central Tethys (Greece).
Löser et al., 2002)terioid colony with corallites arranged in very irregular rows.Septa regularly perforated.Microstructure of large trabeculae.Septa in cross section equal in thickness throughout the whole septum.No septal symmetry or septal generations.Septa not connected to each other.Septal lateral face with pennulae, inner margin smooth.Pali absent.Costae present, confluent.Synapticulae fairly common.The columella varies from absent, to substyliform or styliform and thick by septal fusion.Endotheca consists of very few thin tabulae.Budding intracalicinal, polystomodeal and complete.RemarksAlthough the present specimen has slightly higher septal counts and slightly higher distances of corallite rows, it still compares well to the holotype of Microsolena williamsonensis (NMNH M-547426).The present specimen also compares well to the corallite dimensions and septal counts given for Dimorpharaea japonica Eguchi, 1951, but the type of this species seems to be lost; it could not be found in the collections of the Tohoku University Museum in Sendai, Japan (where the collection of Motoki Eguchi is nearly completely stored;Löser et al., 2002)by the first author in 1999 and 2007.Callovian corals from the Swiss Jura shorter.Septa occasionally connected to each other close to the corallite centre.Septal distal margin unknown, lateral face with numerous thorns, inner margin smooth.Pali absent.Some septa may be attached to the columella.Description Solitary and phaceloid corals.The septa are always free.A lamellar columella is present in some genera.One or two septa may be connected to the columella.
Melnikova et al. (1993)lumella styliform.Endotheca varies.Wall absent.Coenosteum narrow, consists of costae.Budding extracalicinal.Remarks For more details seeMelnikova et al. (1993).lar.Two irregular size orders can be distinguished, that differ in length, but not in thickness.Septa occasionally connected to each other in the centre of the corallite, and to the columella.Septal lateral face with pennulae.Pali absent.Some septa may be attached to the columella.Costae present, sub-confluent to non-confluent, and much more regularly perforated than septa.Synapticulae present and fairly common.Columella styliform and well marked.The endotheca has thin tabulae and extended thin tabulae.Wall absent.Coenosteum extended, consists of costae.Budding extracalicinal.Remarks The problem of separating the numerous and mostly unnamed Eocomoseris species was already discussed in Löser et al. (2021).Only very few species are established but the genus is common in the Jurassic and Cretaceous.Because the corallite dimensions vary much within one colony (as well as being recognisable in the high values for the coefficient of variation for the corallite dimensions in the table above), it is difficult to limit well different species.thinner towards the centre.Symmetry of septa radial and regularly hexameral.Cycles of septa subregular.Septal cycles differ in length and thickness.First two or three septal cycles extend to the corallite centre, later cycles are Other occurrences Lower Kimmeridgian of the European Boreal (Poland), Tithonian to Lower Berriasian of the European Boreal (Czech Republic).Remarks.The genus has not received much attention after its creation.The description of the characteristics is based on the lectotype of Montlivaltia melania.Thin sections are not available from the type specimen, therefore the septal microstructure can only be inferred from the ornamentation of the upper septal margin.Remarks The present specimen is only a fragment.It can only be compared to T. melania because the lectotype of T. melania (MNHN M03534) has only 98 septa.
Description Thamnasterioid colony with corallites arranged in irregular rows.Septa compact.Microstructure of septa of large trabeculae.Septa in cross section equal in thickness throughout the whole septum.No symmetry of septa, but two size orders can be distin- guished, that differ in length (best observable in the centre of the corallite).Septa not connected to each other.Septal distal margin unknown, lateral face with vertical keels.Pali absent.Costae present, mostly confluent.
Synapticulae absent.Columella absent.Endotheca consists of numerous very thin tabulae and exothecal dissepiments.Wall absent.Coenosteum narrow, consists of costae and exothecal dissepiments.Budding extracalicinal.Remarks The genus Montlivaltia is one of the most species-rich genera in the Jurassic and Cretaceous with 224 species in the Jurassic and 74 in the Cretaceous (Lathu- The present specimen compares well to the two syntypes of Montlivaltia icaunensis.Pali absent.All septa of the first generation are attached to the columella.Costae present, confluent.Occasional synapticulae present, but only in the space between corallites.Columella styliform, thickened by the septa connected to it.Endotheca not preserved.Wall absent.Budding extracalicinal.Remarks The present specimen cannot be compared to available type material.It shares some similarities with the syntype MNHN A32299 of Thamnaraea digitalis Etallon, 1864 from the middle Oxfordian of the Swiss Jura.This syntype has the following corallite dimensions and septal counts: ccd, 1.76-2.19;septa, 20-23 (first interval for both).Whereas in the present specimen the corallites are arranged in rows, they are irregularly distributed in the syntype MNHN A32299, which makes a comparison even more complicated.Other two syntypes (MJSN S184) belong to the genus Dendraraea Orbigny, 1849 (according to an additional specimen label signed by Bernard Lathuilière, Nancy, dating from 2010).A lectotype has so far not been designated.Therefore, it is unclear to which genus belongs the species Thamnaraea digitalis.