Paraetmopterus horvathi, Underwood & Schlögl, 2013

Underwood, Charlie J. & Schlögl, Jan, 2013, Deep-water chondrichthyans from the Early Miocene of the Vienna Basin (Central Paratethys, Slovakia), Acta Palaeontologica Polonica 58 (3), pp. 487-509 : 499-502

Paraetmopterus horvathi sp. nov.

Fig. 8A–J.

1991 Centroscymnus sp. ; Barthelt et al. 1991: pl. 1.9.

2006 Centroscymnus sp. B .; Takakuwa 2006: figs. 3.5, 4.4.

Etymology: In honour of Juraj and Tereza Horvath and their children Josef, Tobias, Lia, Benda, Mia, Johanka, and...

Holotype: SNM Z 27473 , lower tooth.

Type locality: Cerová−Lieskové, Vienna Basin, Slovakia.

Type horizon: Lakšárska Nová Ves Formation, late Karpatian (equivalent to latest Burdigalian).

Material.—38 additional lower and 15 upper partial and complete teeth including SNM Z 27474 to SNM Z 27482.

Diagnosis.—Extreme dignathic heterodonty and weak monognathic heterodonty. Lower teeth rectangular in profile, at least twice as high as wide. Mesial edge of tooth smoothly concave, with distal edge almost straight. Cusp small and very strongly distally inclined with apex not reaching distal edge of tooth. Crown enameloid extends about half way down labial face of tooth with semicircular termination. Base of enameloid extends one third of way down lingual face of tooth. Labial face typically with three large foramina, two at base of enameloid towards mesial and distal sides of tooth and a central foramen below the limit of enameloid. Weak horizontal transverse shelf with two foramina at base of enameloid on lingual face. Upper teeth symmetrical with elongate main cusp and single, or rarely double, pair of small lateral cusplets. Cusplets short and robust and closely attached to the main cusp with a continuous cutting edge. Outer edges of cusplets typically overhang lateral part of root. Root labio−lingually compressed and variable in height. Flat to faintly concave basal root face with gentle notch on linguo−basal edge giving the basal face a “heart−shaped” profile in all teeth.

Description.—The lower teeth are close to homodont, while some degree of monognathic heterodonty is present in the upper teeth. The lower teeth are up to 1.4 mm high and 0.75 mm wide. The teeth are somewhat rectangular in labial profile, but have a concave mesial and convex distal edge giving the tooth a general curved profile. The crown and lower half of the root are strongly labiolingually compressed, but the upper part of the root is rather thicker, being expanded lingually. The single cusp is small and very low, with a very strong distal inclination, with the mesial edge being less than 10 degrees from the horizontal (taken as the basal edge of the root). The majority of the cusp mesial edge is straight, but it is convex towards the mesial end of the crown. The cusp reaches almost to the distal end of the crown, and overhangs a small and gently convex distal heel. There is a continuous cutting edge with no serrations. The base of the enameloid on the labial face of the tooth is smoothly curved and often semicircular and reaches to about half the total tooth height. The base of the enameloid on the lingual side of the tooth is also convex, but does not expand as far down the tooth. There is a well developed concavity below the mesial end of the crown on the labial side of the tooth, with a corresponding concavity below the distal heel on the lingual face. The mesial edge of the root is concave, and this is especially pronounced immediately below the base of the crown. The distal edge of the root is typically rather straighter than the mesial edge, and typically comprises a concavity towards the upper and lower ends of the root and a convex region in the centre. The basal edge of the root is straight to weakly convex. The labial face of the root is flat and penetrated by three extremely well developed foramina in most teeth. There are two foramina close to the base of the enameloid to the mesial and distal sides of the tooth midpoint, and a smaller foramen rather lower on the root labial face at a position close to the tooth midline. The lingual face of the root is smooth and thickens upwards from a very compressed region close to the root basal edge to a thickened area just below the base of the crown, the upper edge of which forms a weak shelf. Two large foramina are present on this shelf at the top of the root.

Upper teeth are slightly higher than wide and typically close to symmetrical. There is a well developed main cusp that comprises over half of the height of the tooth, flanked by one or two pairs of small but well developed lateral cusplets. The outermost cusplets are very weakly divergent and slightly overhang the root. The root is weakly bilobed and strongly labiolingually compressed. Viewed lingually, the root has a weakly developed lingual protuberance, below which the rounded to weakly angular root lobes diverge. The root lobes are short and only weakly separated by an obtuse internal angle. The face of the root is flat. There is a well developed foramen close to the apex of the lingual protuberance, and another on the root lingual face close to, or at, the basal edge. A pair of foramina are present below the lateral cusplets on the lingual root face, and additional small foram−

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ina are present just below the base of the enameloid on the la− faces of the cusp, but does not reach the cusp base. The linbial face. gual face of the cusp is strongly convex and unornamented. Remarks.— Paraetmopterus has previously only been re− The root lobes are parallel sided and form an acute angle to corded from the Eocene of France where it is represented by each other. The distal lobe is slightly longer and wider than abundant specimens of P. nolfi Adnet, 2006 . Although very the mesial lobe. The root is labio−lingually compressed with similar overall, P. horvathi differs in a number of ways. The a flat basal face. A weakly developed lingual protuberance is lower teeth show far less heterodonty than those of P. nolfi , present which bears a (poorly preserved) terminal foramen. being consistently higher and more rectangular. The mesial There are large foramina on the mid part of the lateral faces edge of P. nolfi teeth is very strongly and irregularly con− of the root, and in the notch between the root lobes on the lincave, unlike the smoother and less extreme concavity in P. gual side. horvathi , with the positioning of the labial foramina being far Remarks.—Although well preserved, this tooth cannot be more consistent and regular. The upper teeth of P. horvathi readily assigned to a taxon. The overall shape of the tooth is differ from those of P. nolfi in having a more “heart−shaped” very similar to that of species of the somniosid genera Centroroot basal face in most teeth and having more robust lateral scymnus and Scymnodalatias Garrick, 1956 (as figured by cusplets that are more closely attached to the main cusp. Herman et al. 1989). Despite this, more material would be

Although not previously recorded outside the Eocene, needed for a more definite taxonomic assignment. Paraetmopterus appears to be present, but unrecorded, in other of Miocene faunas, having been identified as Centro−

Order Myliobatiformes Compagno, 1973 scymnus. Paraetmopterus therefore appears to be present in the Miocene of Germany ( Barthelt et al. 1991, as Centro− Family Gymnuridae Fowler, 1934 scymnus sp.) and Japan ( Takakuwa 2006, as Centroscymnus Genus Gymnura van Hasselt, 1823 sp. B ). The similarity between the lower teeth of Paraetmo−

Type species: Raja micrura Bloch and Schneider, 1801 ; Recent, Suripterus and Centroscymnus Bocage and Capello, 1864 was name. noted by Adnet (2006). The two genera can, however, be readily distinguished by the form of the upper teeth as de− Gymnura sp. scribed above, and by the presence of an enameloid−covered Fig. 9I . vertical ridge on the labial face of the root of lower teeth, as

Material.—Single imperfect tooth, SNM Z 27484. well as the presence of a nutritive groove on the lingual root face. Description.—The single tooth is small, being about 1 mm Stratigraphic and geographic range.—Eocene to Miocene; wide, and wider than high or deep. The crown is strongly Tethyan Europe. curved, with a concave labial face and rather sharply angled lateral extremities, with a faintly convex region below the

Family Somniosidae Jordan, 1888 cusp. The cusp is broken, but projects lingually. There is a cutting edge between the cusp and the lateral ends of the Somniosidae indet. crown, but this fades and becomes less sharp laterally. The Fig. 8K. crown is smooth on both labial and lingual face. The crown Material.—One upper tooth from sample 17–18, SNM Z overhangs the root on all sides, and there is no uvula or labial 27483. protuberance although the base of the crown on the lingual side is weakly flared. The root is low and smaller than the Description.—This small tooth, about 1.2 mm high, is extre−

crown, being rather lingo−labially compressed. The basal mely gracile and comprises a slender cusp above a strongly

part of the root is damaged by bioerosion, but a wide nutritive bilobed root. The cusp is straight and slightly inclined rela−

groove is present. tive to the root, and is over three times as high as wide. The labial face of the cusp is weakly convex, but becomes more Remarks.—Teeth of Gymnura are present in a large proporstrongly convex towards the base. At the base of the cusp, the tion of Cenozoic chondrichthyan−bearing rocks (CJU perlabial face of the crown forms a bifurcating ridge than contin− sonal observations; David Ward, personal communication ues for half the length of the labial side of the root lobes. A 2011), with Neogene specimens having been figured on sevweak crest is present on each of these basal lobes of the eral occasions (e.g., Cappetta 1970) but are commonly overcrown. A weak cutting edge separates the labial from lingual looked because of their small size. In addition, the tooth mor− Ą

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phology appears to be very conservative within the genus, and the dentitions of extant species are poorly known.

Neoselachii incertae sedis

Genus Nanocetorhinus nov.

Type species: Nanocetorhinus tuberculatus gen. et sp. nov.; see below.

Etymology: From the overall resemblance to the teeth of the planktivorous shark Cetorhinus de Blainville, 1816 , but differ in their vastly smaller size.

Diagnosis.—Teeth minute, rarely exceeding 1 mm high, with a single cusp overlying an irregular to bilobed root. Weak heterodonty other than compressed symphyseal teeth. Cusp slender, over three time as long as wide, straight or faintly curved. Cusp faces strongly convex with very well developed cutting edge bearing weak and very irregular serrations. Labial face of cusp with well developed granulae or irregular granulate ridges. Flared collar at base of cusp with fine pitted ornament. Root rather irregular with two lobes present to a greater or lesser degree. Basal face of root with irregular foramina or often incompletely closed over resulting in single very large basal foramen.

Remarks.—The teeth of Nanocetorhinus gen. nov. do not closely resemble those of any other neoselachian genus, so their affinity is uncertain. While the overall shape of the teeth is similar to that of Cetorhinus , there are many differences in the ornamentation, presence of the “collar”, and form of the root and its vascularisation, while the characteristic gill rakers of Cetorhinus were not recorded associated with teeth Nanocetorhinus gen. nov. Indeed, the simple crown and rather irregular root is reminiscent of that seen in many, unrelated, planktivorous chondrichthyans. The small size of these teeth, presence of a “collar” and frequent open base of the root may suggest that these are dermal denticles, and not oral teeth. Despite this, the irregular shape of the root with discrete root lobes and lack of a flat basal face are not seen in any denticles of extant chondrichthyans that have been figured or observed (CJU personal obserwations); and lack of denticles of this overall morphology amongst extant chondrichthyans all suggest that Nanocetorhinus does not represent denticles but represents oral teeth of an enigmatic taxon.

Figures

Fig. 9. Miocene neoselachian and myliobatiform sharks of Nannocetorhinus and Gymnura teeth respectively, from Cerová section in Malé Karpaty, Slovakia. A–H. Nannocetorhinus tuberculatus gen. et sp. nov. A. Holotype, SNM Z 27485, bed 21–22, in labial (A1) and lingual (A2) views. B. SNM Z 27486, bed 8–9, in labial (B1) and lingual (B2) views. C. SNM Z 27487, bed 17–18, in labial (C1) and lingual (C2) views. D. SNM Z 27488, bed 8–9, in labial (D1) and lingual (D2) views. E. SNM Z 27489, bed 13, in labial (E1) and lingual (E2) views. F. SNM Z 27490, bed 17–18, in labial (F1) and lateral (F2) views. G. SNM Z 27491, bed 20–21, in labial (G1) and lingual (G2) views.H. SNM Z 27492, bed 20–21, in labial (H1) and lingual (H2) views, detail (H3). I. Gymnura sp., SNM Z 27484, bed 14, in occlusal (I1) and basal (I2) views.