Belemnobatis undetermined

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 : 325

BELEMNOBATIS SP. ( FIG. 6A–D )

Material: Two complete teeth, MPZ 2005-10 and MPZ 2005-11.

Occurrence: Sample 5 from the highstand systems tract representing a deepening succession of fully marine conditions (facies 3) of the upper Blesa Formation (Upper Barremian) of the Oliete subbasin.

Description: The teeth are 0.75 mm in height and 1.7 mm in maximal width, with a high, rounded crown that is as broad as it is long, and with acute lateral angles. The crowns are cuspidate with a poorly developed apex, and a weak transverse cutting edge. The labial face has no central protuberance, only a rounded labial rim that overhangs the root, and is ornamented with a small number of weak folds along the labial edge of the crown. The lingual edge has a short and narrow central uvula, with a rounded extremity that follows the lingual contour. There are no marginolingual uvulae. The root is massive, high and vertical, and surpasses the crown lingually. The lobes are separated by a deep narrow groove, which closes towards the basal face of the root. The margino-lingual faces have a pair of foramina, and the collar is very marked.

Remarks: The taxonomy of Late Jurassic batoids is in a disastrous state and detailed anatomical revisions have to be performed before their systematic position can be recognized with any confidence, despite several recent attempts. Three rhinobatoids from the Late Jurassic were described based on skeletal material and most isolated teeth of similar morphology were ascribed to either one of those. Unfortunately, the holotype of the first taxon, Asterodermus platypterus Agassiz, 1843 from the Tithonian of southern Germany, lacks the skull so that it is not possible to establish its dental morphology. Two additional batoids, Belemnobatis sismondae Thiollière, 1854 and Spathobatis bugesiacus Thiollière, 1854 , occur in the Kimmeridgian lithographic limestones of Cérin, France. Belemnobatis sismondae was also reported from the Kimmeridgian of Nusplingen ( Schweizer, 1964). Although Asterodermus platypterus resembles Spathobatis bugesiacus in scale morphology, isolated teeth generally assigned to Asterodermus differ significantly and are more similar to those of Belemnobatis . Cavin et al. (1995) and Leidner & Thies (1999) listed several dental features to distinguish Spathobatis from Belemnobatis . Identifying Asterodermus on the basis of placoid scale and tooth morphologies were based on finding additional characters to differentiate the three genera ( Kriwet & Klug, 2004). For instance, the rostrum is long in Asterodermus and Spathobatis but rather short and blunt in Belemnobatis sismondae . The rostrum of Belemnobatis morinicus , however, is also long and comparable with that of Spathobatis and Asterodermus ( Cavin et al., 1995) . Leidner & Thies (1999) tentatively identified all Late Jurassic batoids from the lithographic limestones of southern Germany as belonging to Asterodermus .

Many isolated teeth have been assigned to different species in the past (e.g. Thies, 1983; Candoni, 1995). The inability to identify these species when larger samples of isolated teeth are examined indicates that species of Spathobatis (e.g. S. bugesiacus ) are characterized by a high degree of heterodonty ( Underwood, 2002). Underwood agrees with Cavin et al. (1995) that teeth of Belemnobatis may be separated from teeth of Spathobatis in having a gracile lingual uvula and slightly flared lateral edges of the crown and root. Subsequently, Underwood & Ward (2004) identified several additional species of Belemnobatis and Spathobatis from the Bathonian of England, stating that Asterodermus should be restricted to the holotype until the tooth morphologies of specimens referred to this species are better known.

According to the classification of Cavin et al. (1995), the Spanish specimens belong to Belemnobatis because of its relatively weak transverse crest, poor development of the central cusp, narrow uvula, and a root with a vertical labial face. A specific identification is not possible, because of the scarcity of material.

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.