Lower Permian (Artinskian) chondrichthyan tooth remains (Petalodontidae) from Dovje (Karavanke Mts., NW Slovenia)

Fossil remains of chondrichthyan tooth bases (roots) were found in Lower Permian beds exposed along the forest road between Dovje and Plavški Rovt. These layers are part of the clastic development of the Trogkofel Group beds. They are composed of an alternation of dark to light-grey shales, siltstone, and sandstone with rare beds of the conglomerate. Within the clastic succession, layers or lenses of dark-grey to black limestones (biosparitic, biomicritic and oolitic) and limestone breccias occur. The limestone consists remains of algae, fusulinids, brachiopods, and mostly crinoids ( Palermocrinus and Entrochus ). Detail study has shown that two remains of tooth bases belong to the genus Petalodus , one of them to the species Petalodus ohioensis . The bases are tongue-shaped and


Introduction
The Petalodontiformes are a small intriguing group of late Paleozoic chondrichthyans, ranging from the Carboniferous (Mississippian) to the Permian. Up to now, there are about 17 genera referred to Petalodontiformes, but most are known principally from isolated teeth (Ginter et al. 2010;Lund et al., 2014). Petalodus is the longest-known petalodont cosmopolitan genus. The late Paleozoic chondrichthyans (»shark«) record from Slovenia consists of complete or partial remains of petalodont teeth (Petalodontidae gen et. sp. ident. and Petalodus ohioensis) and one tooth of Glikmanius cf. occidentalis (for the references and the list of localities see Table 1).

Geological and Stratigraphical settings
In the Southern Karavanke Mts. the outcrops of Upper Paleozoic (Upper Carboniferous and Lower Permian) fossiliferous shallow marine deposits are scattered between Solčava and Dovje (Fig. 1). The broadest and best exposed Lower Permian beds are present north of Tržič, in the vicinity of famous fossil sites Dovžanova soteska and Jelendol (Novak, 2007;Novak & Skaberne, 2009). In the western part of Southern Karavanke Mts. Lower Permian beds are mainly exposed  Peternel, 1995 in Javorniški Rovt and Pristava, and between Planina pod Golico and Dovje village (Novak & Skaberne, 2009). The lithostratigraphic subdivision of Lower Permian rocks in the Southern Karavanke mountains is composed of the Grenzland Fm., Zweikofel Fm. and on top the Trogkofel Group (Novak & Skaberne, 2009, 199). In the youngest beds of the Trogkofel Group, carbonate and clastic developments are distinguished. The carbonate part is represented by light-grey, dark-red, and rose-red reef fossiliferous limestones and fore-reef limestone breccias in some parts. The Trogkofel limestone is massive (as reef bioherm) or thick-bedded and rich in fossils. The clastic development of the Trogkofel Group beds is composed of the alternation of dark to light-grey shales, siltstone, and sandstone with rare beds of conglomerate (Novak & Skaberne, 2009). Within the clastic succession, layers or lenses of dark-grey to black limestones (biosparitic, biomicritic and oolitic) and limestone breccias occur, containing rock-forming remains of algae, fusulinids, brachiopods, rare corals, and crinoids (Novak & Skaberne, 2009). The age of the Trogkofel Group (with Trogkofel limestone) in the Southern Karavanke is middle to late Artinskian, with a thickness of a maximum of 400 meters (Novak & Skaberne, 2009).
The outcrop of the newly discovered chondrichthyan tooth fragments is located along the forest road between Dovje and Plavški Rovt (Fig. 2). Layers of dark-grey limestones and an alternation of light-grey shales and siltstone are exposed. All beds are extremely fossiliferous with numerous disarticulated crinoid remains. The remains of crinoids are mostly fully disarticulated parts (ossicles) of stems (columnals), arms, pinnules, and rarely crinoid crowns (Lach et al. 2013). Crinoid remains were not yet the subject of a thorough paleontological investigation, but preliminary research shows the presence of the crinoid genera Palermocrinus and Entrochus, with probably some members of Codiacrinidae (Lach et al., 2013;Ramovš & Sieverts-Doreck 1968). The associated fauna is composed of brachiopods (productids and spiriferids), bivalves, gastropods, foraminifers (fusulinids), algae (Shamovella-Archaeolithoporella), and fenestellid bryozoans which are with the crinoids, form the main biotic component in some parts. Similar crinoidal limestone with Palermocrinus togatus, with higher carbonate content, is known at Pristava in Javorniški Rovt. The age of the outcrop with new fossil tooth remains is Artinskian (Novak & Skaberne, 2009;Novak M., personal comm.).

Materials and methods
Specimens were discovered by Jure Zupanc around the year 2000 and are stored in his private geological collection. For the specimens described here, we use working identification numbers JZC 001 (Fig. 4) and JZC 002 (Fig. 5). Both specimens were prepared only with minor mechanical tools (needles) and measured with a metal hand vernier caliper. The specimens were photographed using a Nikon D7200 camera coupled with an AF-S Micro NIKKOR 60mm f/2.8G ED lens. Photos of specimens were additionally edited with the advanced photo editing program Adobe Photoshop Lightroom which enhanced the visibility of some features.
Our description of the tooth base (Fig. 3) follows combined terminology suggested by Dalla Vecchia, (1988

Systematic Paleontology
Systematics follows the taxonomic views of Ginter et al. (2010)   Material: One specimen of base of petalodontid tooth (Fig. 4). Specimen (JZC 001) was discovered by Jure Zupanc and is stored in his private geological collection. The specimen represents the complete tooth base (Fig. 4A-C) of a typical petalodont tooth. The tooth crown is missing.

Description:
The base is triangular in tongue shape and comes to a rounded point in the distal edge (base end). Transversely the base is oval.
The mesiodistal width is 30 mm, and the total length is 36 mm. The maximal lingual-labial thickness of the tooth base is 6.4 mm. The lingual side of the base is bent to the labial side. On the surface of the lingual side, a few oval-shaped foramina are visible, on faint traces of ridges. On top of the base, the distal crown tongue is poorly preserved and overhangs the base. The labial side of the base has four elongated ridges, with no visible foramina, partially covered with a matrix. Fig. 3. Anatomical terminology of petalodontid tooth (Petalodus). Adapted from Dalla Vecchia, (1988), Robb (2003), and Gai et al. (2021). Sl. 3. Anatomska terminologija petalodontidnega zoba (Petalodus). Prirejeno po Dalla Vecchia, (1988), Robb (2003) in Gai et al. (2021). Petalodus cf. ohioensis Safford 1853 Figure 5 Material: One specimen of base of petalodontid tooth (Specimen JZC 002) (Fig. 5). The remains represent a fragmentary but typical petalodont tooth base ( Fig. 5A-E). The tooth crown is missing.

Description:
The base is triangular in shape and it is transversely oval. The mesiodistal width of the preserved base is 33 mm. The maximal lingual-labial thickness of the preserved tooth base is 9.5 mm. Labially the base is more concave and lingually convex. On both sides (lingual and labial) three elongated (vertical) ridges are present. On the lingual side, the oval-shaped foramina are visible on all ridges. On the bordered part (top of the base), a small part of the distal crown tongue is present, with two rows of ridges. On both distal surfaces of the specimen, the spongy tissue is visible. According to Zangerl et al. (1993), this tissue is circumpulpar trabeculine (cavities) and trabecular dentine, or osteodentine by Dalla Vecchia, 1988 andGai et al., 2021 (Fig. 5D-E).

Discussion and Conclusion
Teeth of Petalodus are often the most common chondrichthyan fossil remains reported from the Carboniferous and Permian rocks of the USA, Europe, Russia, and China (Ginter et al. 2010, 141;Dalla Vecchia, 2008;Gai et al. 2021). The remains are mainly isolated teeth. Petalodus ohioensis is well known from Upper Carboniferous and Lower Permian beds and it is widespread (Hansen, 1985;Elliott et al, 2004, 277-278;Ginter et al. 2010, 141). The specimen presented here (JZC 001) (Fig. 4), preserved as a tooth base, is typical of Petalodus ohioensis. The shape of the tooth base is very similar in shape and dimensions to specimens presented by Brusatte (2007, 3, fig. 2), Harper (2018, 4, fig. 1), Ramovš & Bedič (1993, 149, fig. 1) and Ramovš (1997, 110, fig. 1). All these specimens come from Upper Carboniferous strata and are probably from the anterior part of Petalodus ohioensis jaw, based on shape and size of teeth base (Elliott et al, 2004, 277, fig. 5A-B). Even though our second specimen (JZC 002) (Fig. 5) is broken, we attribute it to the genus Petalodus. Its shape and dimensions and comparison with other specimens (see Brusatte, 2007;Harper, 2018;Ramovš & Bedič 1993) allow us to classify it as Petalodus cf. ohioensis. The new finding increases the petalodont diversity in the Southern Alps, and also sheds new light on the distribution and stratigraphic range of petalodonts in Slovenia and this part of Europe.