Lissodus sardiniensis, Fischer & Schneider & Ronchi, 2010

Fischer, Jan, Schneider, Jörg W. & Ronchi, Ausonio, 2010, New hybondontoid shark from the Permocarboniferous (Gzhelian-Asselian) of Guardia Pisano (Sardinia, Italy), Acta Palaeontologica Polonica 55 (2), pp. 241-264 : 256-260

Palaeobiogeography of Lissodus in freshwater habitats

Lissodus is verified in nearshore marine deposits since the Late Devonian (Frasnian) ( Trinajstic and George 2007) and for the remaining Late Palaeozoic ( Johnson 1981; Tway and Zidek 1983; Duffin 1985; Derycke et al. 1995; Ivanov 1996, 1999, 2000, 2005; Lebedev 1996; Ginter 2002; Duncan 2004; Fischer 2008). From the current state of knowledge the first doubtless occurrence in non−marine deposits is from the Late Carboniferous (Stephanian B/C after Pseudestheria cf. limbata, Schneider et al. 2005a ) of the Donetsk Basin, Ukraine (JWS, fieldwork 2002) ( Fig. 10 ). Nevertheless, shark egg capsules of xenacanthids, i.e., Fayolia , and of hybodonts, i.e., Palaeoxyris , are known from true freshwater habitats (river deposits) at least since the Late Viséan early molasse deposits of the Variscan orogen in Germany ( Rössler and Schneider 1997; Schneider et al. 2005 b). Highly frequent glacio−eustatic and tectonically induced transgressions and regressions in the time frame from the Viséan to the Westphalian (Moscovian) form the background (comparable to the “estuary effect” by Park and Gierlowski−Kordesch 2007) for the colonisation of brackish and freshwater environments by initially marine fishes, and most probably by Lissodus too ( Schneider and Reichel 1989; Rössler and Schneider 1997). Since the Late Stephanian (Gzhelian–Asselian) different species ( L. lacustris , L. lopezae , and L. sardiniensis sp. nov.) form part of a highly diverse freshwater shark−association ( Orthacanthus – Xenacanthus – Bohemiacanthus – Sphenacanthus – Lissodus ,

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Schneider and Zajíc 1994; Schneider et al. 2000) in the non−marine inter− and perimontane basins of Europe ( Figs. 10 , 11 ). In North America the first occurrence of Lissodus is reported from the Early Permian (late Artinskian– Kungurian) with L. zideki ( Johnson 1981; Zidek et al. 2004) ( Fig. 10 ).

It should be borne in mind that the tiny teeth of Lissodus from non−marine environments have been and will be overlooked in black shales, the main type of lacustrine sediment lithology investigated. In Europe, Lissodus became increasingly well known following the acid preparation of lacustrine limestones for ichthyolits by Gebhardt (1986, 1988). Further discoveries could easily change these following first tentative palaeogeographic interpretations.

As far as is known, L. lacustris is the commonest species group of this genus with the widest distribution in Stephanian C (Gzhelian–Asselian) ( Fischer and Schneider 2007, 2008; Fischer 2008) from the Donetsk Basin ( L. cf. lacustris ), across the central− and western Bohemian basins of the Czech Republic ( L. cf. lacustris ; Zajíc 2000), the Saale and Thuringian Forest basins in eastern Germany ( L. lacustris Gebhardt, 1988 ), to the Saar−Nahe Basin in western Germany ( L. lacustris ; Hampe 1991; Krätschmer 2005) (see Figs. 11 , 12A ). All these basins were connected during the Stephanian by a complex drainage system following different fracture zones ( Schneider and Zajíc 1994; Schneider et al. 2000) allowing interbasinal migrations. The Central European Variscan orogen was levelled to low mountain ranges by at least the beginning of the Stephanian B ( Roscher and Schneider 2006). Thus, the Variscan belt was not an insurmountable migration barrier to aquatic organisms between the northern and southern flanks of the Variscides ( Werneburg et al. 2007). A connection between the Saar−Nahe Basin to the eastern Thuringian Forest and Saale basins is here assumed alongside the north−eastern runoff direction of the Saar Basin or along the northern part of the Hunsrück southern border fault zone. A connection to the Bohemian basins might have followed the NW−SE striking Elbe lineament. Unfortunately, the only occurrence of Upper Carboniferous sediments in this area of the Döhlen Basin gives no hint of an extended river system (Schneider 1994). Therefore, a faunal exchange along the NW−SE striking Franconian lineament is much more plausible than along the Elbe Zone. Connection of the eastern Donetsk Basin to the Middle European basins is still unclear, but can be assumed by the occurrence of a typical Euramerian freshwater shark association ( Schneider and Zajíc 1994).

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The Puertollano Basin in central Spain yielded two different species of Lissodus and one further record not designated to species level ( Schneider et al. 2000; Soler−Gijón and Moratalla 2001). L. lopezae Soler−Gijón, 1997 was probably a rare, endemic species whereas L. cf. zideki ( Soler−Gijón 1993) was much more common. We can assume that the latter migrated at the end of Stephanian C into the eastern Saar−Nahe Basin and there replaced the local L. lacustris ( Boy and Schindler 2000) ( Fig. 12A ). If this was so, this migration probably took place from Spain using river systems linked to transform faults of the NW−SE striking Bay of Biscay Fracture Zone and toward to the N−S striking French Grand Sillon Houllier Fracture Zone in the south. Within this fault system, the migration into the eastern−situated Saar−Nahe Basin was possible. This is in concordance with Boy and Schindler (2000) who assumed a faunal immigration into the Saar−Nahe Basin from the west across France. Additionally, L. cf. zideki might be the ancestor of the North American L. zideki ( Johnson 1981; Zidek et al. 2004), which first emerged in the late Early Permian (Artinskian−Kungurian) of Texas, Oklahoma and Nebraska. There, migration might have occurred alongside the Bay of Biscay Fault Zone northwards to the Rheic Ocean, which formed an embayment from the Panthalassa Ocean to mid−European areas until final closure during the Middle Permian according to a new palaeogeographic model by Kroner in Schneider et al. (2006) and Roscher and Schneider (2006). Generally, the fault and river systems linked to the marine realm could act as migration routes from the sea via rivers into the continental basins, likewise euryhaline fishes could migrate between different drainage systems via the sea. This does not stringently require marine influences on intracontinental basins as claimed by Schultze (2009).

The picture from the Lower Rotliegend (middle Asselian– early Sakmarian) differs from the Stephanian ( Fischer and Schneider 2007, 2008). There are only local spots with possible endemic species of Lissodus in more or less restricted areas ( Fig. 12B ). L. sardiniensis sp. nov. might represent a descendant of the Spanish Lissodus species because of the resemblance of the teeth of L. sardiniensis sp. nov. with L. lopezae and L. cf. zideki , as described above. The former connection of Sardinia to Middle and Western Europe was most likely via the Bay of Biscay and Grand Sillon Houllier fault zones with no insurmountable migration barriers. L. cf. lacustris from the Early Permian (Asselian) of the Grüneberg Basin in the northeast German Brandenburg depression ( Gaitzsch 1995) seems to be an endemic relict of the stratigraphic older form L. lacustris . Moreover, L. sp. (NM) from the Saar−Nahe Basin shows particularly strong affinities to L. zideki ( Hampe 1996) . Currently undetermined teeth and spines of Lissodus , which show some affinity with L. cf. zideki , are known from the middle Sakmarian (i.e., upper Autunian) Buxières Formation of the Aumance Basin, French Massif Central ( Steyer et al. 2000; Kaulfuss 2004). Spines with hook−like denticles of the same age were found in the Usclas−St Privat Formation in the Lodève Basin of southern France. All these spotty occurrences or “relicts” might indicate a cut off of migration routes following the destruction of interbasinal river connections by Franconian tectonic movements around the Stephanian C/Lower Rotliegend boundary (Gzhelian–Asselian) at 302–297 Ma followed by a strong decrease in the diversity of freshwater sharks in most European basins ( Fig. 11 ; Schneider and Zajíc 1994; Schneider et al. 1995, 2000) and possibly endemic evolution in the former trans−European (?–Euramerian) distribution area (Schneider 1989; Schneider et al. 2000). The increasing rarity and subsequent disappearance of Lissodus in the European basins is part of a step−wise extinction of the Carboniferous−type fish faunas of the palaeotropics during the Early Permian (Cisuralian). This step−wise extinction was caused by the interference of climatic and orographic physio−geographic processes. The general aridisation trend during the Permian shows a large scale change between dry and wet phases with a cyclic 7 to 9 Ma frequency ( Roscher and Schneider 2006). Each subsequent wet phase is dryer than the foregoing wet phase. These, together with the increasing peneplanation of the Variscan orogeny as well as short−term but intense volcano−tectonics, increasingly prevented the development and existence of large permanent river systems. Increasing seasonal climate with augmented seasonal water discharge of rivers is indicated by extended braided river facies in the outspreading red beds during the European Early Cisuralian ( Schneider and Gebhardt 1993; Schneider et al. 2006; Roscher and Schneider 2006). Extended large lakes appear in each wet phase but they are increasingly impoverished in their fish faunas. The LOD of Lissodus and Orthacanthus in the European basins falls into the fourth wet phase of Roscher and Schnei− der (2006), to which the Buxières and the Usclas−St Privat lakes belong. Acanthodes , which is often associated with Lissodus , has its LOD in the following fifth wet phase. The fourth wet phase marked the last occurrence of perennial lakes of the black shale facies in the disappearing palaeotropics, the biomes 1 to 3 of Ziegler (1990). In subsequent wet phases they are substituted by playa and sabkha lakes of semiarid and arid environments in the equatorial belt between 33 ° N and 33 ° S. Of course, freshwater sharks would not normally exist in temporary playa lakes. One interesting question remains unanswered so far—are there refuges for freshwater−adapted sharks such as Lissodus outside the equatorial arid belt in the areas of biomes 4 to 6 northerly and southerly of 33 ° latitude (compare with Roscher et al. 2008) in the Permian? Otherwise, the above discussed LOD of the Euramerian Palaeozoic freshwater species of Lissodus is the real LAD of these forms.

Figures

Fig. 10. Correlation chart of some late Pennsylvanian and Permian continental basins of Europe and marine−influenced Texas, USA. Grey circles indicate the occurrence of Lissodus remains (stratigraphy after Colmenero et al. 2002, Roscher and Schneider 2005, and Lucas 2006).

Fig. 11. Palaeobiogeography of hybodonts, ctenacanths, and xenacanthids from the Lower Rotliegend, Stephanian C (Late Carboniferous and Early Permian) based on current knowledge: B, Bohemiacanthus; L, Lissodus; O, Orthacanthus; P, Plicatodus; S, Sphenacanthus; T, Triodus; X, Xenacanthus; below the horizontal line – occurrences during Stephanian C (late Gzhelian–early Asselian), and above the horizontal line—occurrences during Lower Rotliegend (middle Asselian–early Sakmarian) (after Fischer 2005, new arranged after Schneider and Zajíc 1994). Palaeogeographic position of important Permo−Carboniferous basins (after Fischer 2005 and Roscher and Schneider 2006), the Late Permian Northern and Southern Permian Basin are omitted: AU, Autun Basin; BLG, Blanice Graben; BCG, Boskovice Graben; BU, Bourbon l’Archambault Basin; CA, Carpathian Basin; CR, Carnic Alps; DB, Donetsk Basin; DÖ, Döhlen Basin; EB, Erzgebirge Basin; EBL, Elbe Lineament; FL, Flechting Block; FRL, Franconian Lineament; FR, Franconian Basin; GBFZ, Golf of Biscay Fracture Zone; GMFZ, Gibraltar Minas Fracture Zone; GP, Guardia Pisano Basin; GSH, Grand Sillon Houllier Fracture Zone; HRF, Hunsrück Fracture; IF, Ilfeld Basin; IS, Intra Sudetic Basin; KP, Krkonoše Piedmont Basin; LC, Lu Caparoni Basin; LO, Lodève Basin; MO, Montceau les Mines Basin; NGVC, North German Volcanite Complex; NS, North Sudetic Basin; PBF, Pays de Bray Fracture; PD, Perdasdefogu Basin; PU, Puertollano Basin; RGL, Rhein Graben Lineament; RÜ, Rügen; SB, Saale Basin; SNB, Saar−Nahe Basin; ST, St. Etienne Basin; SV, Salvan−Dorénaz Basin; TF, Thuringian Forest Basin; TTFZ, Tornquist−Teysseyre Fracture Zone; WCB, Western and Central Bohemian Basins; WEI, Weissig Basin; ZÖ, Zöbingen.

Fig. 12. Distribution areas of different Lissodus species in Europe. A. Latest Carboniferous/earliest Permian (Stephanian C): Lissodus lacustris is the most common species; Lissodus lopezae is restricted to Central Spain, and Lissodus cf. zideki shows a migration into the eastern Saar−Nahe Basin documenting the existence of migration possibilities between the single basins, other routes to the northwestern Rheic Ocean and to the southern Sardinia are just assumed. B. Early Permian (Asselian%Sakmarian): Lissodus cf. lacustris is a relic of Lissodus lacustris; Lissodus sp. (NM), Lissodus sp., and Lissodus sardiniensis sp. nov. are considered to be endemic relicts of L. cf. zideki in its former occurrence area; and the appearance of L. zideki in the late Early Permian of North America is also regarded as the result of NW migration.