Rhinobatos, SP., LINK, 1790

Kriwet, Jürgen, Nunn, Elizabeth V. & Klug, Stefanie, 2009, Neoselachians (Chondrichthyes, Elasmobranchii) from the Lower and lower Upper Cretaceous of north-eastern Spain, Zoological Journal of the Linnean Society 155 (2), pp. 316-347 : 327-329

‘ RHINOBATOS ’ SP. ( FIG. 6M–T )

Material: A well-preserved tooth, MPZ 2005-15 ( Fig. 6M–P ); an isolated tooth crown with root remnants, MPZ 2005-16 ( Fig. 6Q–T ).

Occurrence: Samples 4 and 6 from floodplain environments with channel deposits (facies 2 and 3, respectively) of the Mosqueruela Formation (Cenomanian), Aliaga subbasin.

Description: The tooth crown is broader than it is long, and is not cuspidate. The straight transverse ridge is sharp and lingually placed. The labial edge is rounded in occlusal view, with a slight central protuberance. The lingual face is abrupt with a marked concavity at the upper part of the median uvula in profile view. The central uvula maintains contact with the lingual contour, and is short and broad, with a rounded extremity not roofing the root notch. There is one pair of well-developed lateral uvulae. The root is slightly displaced lingually and extends laterally beyond the crown. It is narrow, with a pronounced lingual notch and broad nutritive groove separating two root lobes, which are subtriangular in basal view. There are a pair of margino-lingual foramina. A single foramen opens into the nutritive groove.

Remarks: This species is assigned to rhinobatoids primarily on the basis of its lingually displaced tooth root, the lobes of which become narrower lingually on both sides of the groove, and a straight and sharp transverse crest dividing the tooth crowns into a labial and lingual portion. In this, they are very similar to teeth generally assigned to Rhinobatos and many similar fossil teeth of rhinobatoid-like appearance from the Cretaceous. Only a few specimens, mainly from the Upper Cretaceous limestones of Lebanon, are known by articulated and more or less complete skeletons. The differences found in the dental morphology of the described species indicate that the fossil genus Rhinobatos comprises different rhinobatid genera ( Kriwet, 1999a). This assessment is also supported by a phylogenetic analysis by Brito & Dutheil (2005) considering several extant and fossil batoids.

Nominal fossil species attributed to Rhinobatos are listed in supplementary Appendix S1. The large number of teeth assigned to Rhinobatos without specific identification (16) exemplifies the problems in dealing with isolated rhinobatoid teeth. Unfortunately, rhinobatoids are rather conservative in dental morphology, rendering the identification of true Rhinobatos species extremely difficult and a careful revision of fossil Rhinobatos species is necessary but beyond the scope of the present paper. Teeth of R. kiestensis Cappetta & Case, 1999 , which are very similar to teeth of the extant batoid genus Aptychotrema , also exemplify this problem very well. A preliminary phylogenetic analysis of batoids from the Cretaceous of Lebanon also supports the polyphyly of fossil Rhinobatos species ( Brito & Dutheil, 2005). The few teeth described herein share certain characters with several of the species described from the Upper Cretaceous of Lebanon by Cappetta (1980b), most notably with ‘ R. ’ primarmatus, which has a similar crown shape in oral view, and development of the central and lateral uvulae, and with ‘ R. ’ intermedius, which has a similar structure of the root, especially in terms of the very well-developed labial notch. ‘ R. ’ primarmatus, however, has a lower and more cuspidate crown than that of this specimen, whilst ‘ R. ’ intermedius has a significantly narrower central uvula, and no lateral uvulae. Although the Spanish species seems likely to be a new taxon, the scarcity of material and unresolved systematic position of most Cretaceous rhinobatoids precludes defining a new species. We therefore tentatively assign the teeth to the genus Rhinobatos .

SUBORDER RHINOBATOIDEI FAM. INDET. ( FIG. 7A–D )

Material: A single lateral tooth, MPZ 2005-17.

Occurrence: Sample 4 from floodplain environments with channel deposits (facies 2) of the lower part of the Mosqueruela Formation (lower Cenomanian), Aliaga.

Description: This is a relatively large tooth (> 2 mm wide), with a massive, high and globular crown with a sub-hexagonal outline in occlusal view and a flat occlusal surface. The transverse crest is almost absent and there is no clear boundary between the oral and the lingual face. The labial margin is straight and the labial face is fairly abrupt, with a broad, rounded apron overhanging the root. The lingual edge has a massive and wide-based central uvula that also juts out over the narrow, vertical root. The root has a margino-lingual and margino-labial pair of foramina.

Remarks: This tooth shares many characters with the genus Pseudohypolophus ( Cappetta & Case, 1975) . However, Pseudohypolophus has a lower and more distinctly hexagonal crown, compared with this tooth, which is much more globular, and with a more rounded lingual margin. The crown shape is more similar to that of Protoplatyrhina ( Case, 1978) , which also has a similar short extension of the central uvula. However, Protoplatyrhina is only known from the Maastrichtian. Unfortunately, the single, poorly preserved specimen prevents an accurate identification of this tooth.

Figures

Figure 6. A–D, Belemnobatis sp., anterior tooth. A, labial view. B, lateral view. C, lingual view. D, occlusal view. E–L, Spathobatis sp. E–H, antero–lateral tooth. E, labial view. F, lateral view. G, lingual view. H, occlusal view. I–L, lateral tooth. I, labial view. J, lateral view. K, lingual view. L, occlusal view. M–P, Rhinobatoidei indet. M, labial view. N, lateral view. O, lingual view. P, occlusal view. Q–T, Rhinobatos sp. Q, labial view. R, lateral view. S, lingual view. T, occlusal view. All scale bars equal 0.5 mm.

Figure 7. A–D, Rhinobatoidei indet. A, labial view. B, lateral view. C, lingual view. D, occlusal. E–T, Platypterix venustulus gen. et. sp. nov. E–H, anterior male tooth. E, labial view. F, lateral view. G, lingual view. H, occlusal view. I–L, lateral male tooth. I, labial view. J, lateral view. K, lingual view. L, occlusal view. M–P, anterior female tooth. M, labial view. N, lateral view. O, lingual view. P, occlusal view. Q–T, lateral female tooth. Q, labial view. R, lateral view. S, lingual view. T, occlusal view. U–X, Celtipristis herreroi (Kriwet, 1999b). U, labial view. V, lateral view. W, lingual view. X, occlusal view. All scale bars equal 0.5 mm.