Synechodus prorogatus sp. nov., 2003

Kriwet, Jürgen, 2003, Neoselachian remains (Chondrichthyes, Elasmobranchii) from the Middle Jurassic of SW Germany and NW Poland, Acta Palaeontologica Polonica 48 (4), pp. 583-594 : 588-591

Synechodus prorogatus sp. nov.

Fig. 3D, E, L .

Holotype: An antero−lateral tooth, BGR X 12503 , Fig. 3D .

Additional material: A tooth crown fragment (lateral cusplet), BGRX 12504,aswellasbioerodedcrown,BGRX12510,attributed tothisspecies.

Type locality: Kłęby near Golczewo, NW Poland.

Type horizon: Drill core Kłęby 1/37: 244.8–245.7 m, Callovian.

Etymology: The species name is derived from prorogatio, the Latin word for prolongation in reconsideration of the labial enameloid expansions. The name is masculine in gender.

Occurrence.—Only known from the type locality.

Diagnosis.—A species of Synechodus characterised by very small teeth. Antero−lateral teeth asymmetrical with elongated mesial and shorter distal heel. Main cusp labio−lingually flattened. First pair of lateral cusplets pointed and high. Up to three small and widely fused lateral cusplets on mesial heel. Second distal cusplet very small. Labial ornamentation consisting of a mesio−distal fold parallel to the cutting edge. Additional horizontally orientated, irregular folds below lateral heels present and in contact with the main labial sculpture creating a narrow band of reticulate−like ornament. Two labial enameloid prolongations extending basally on labial root laminae. Lingual face with short, vertical folds not reaching the base of the crown.

Differential diagnosis.—The new species differs from all other Synechodus species:

– in the presence of vertical, basally directed labial enameloid prolongations at the basal margin of the crown. The labial margin in all other species is straight to concave and continuous.

– in the presence of a labial fold, which is continuous mesio−distally and parallel to the well−developed cutting edge.

– in the horizontal, irregular folds below the lateral heels creating a narrow band of anastomosing− and reticulatedlike ornamentation on the labial face and forming a crestlike structure on the lingual heels.

Description.—The single complete tooth is rather small measuring only 1.22 mm mesio−distally and 0.67 mm in height. The crown base is considerably mesio−distally elongated and high, and slightly asymmetrical with the mesial heel being longer than the distal one. The main cusp is slender, triangular in labial view but compressed labio−lingually to some extend and slightly curved lingually. The apex is pointed and slightly bent distally. There is one pair of well developed, pointed and slightly divergent lateral cusplets. The distal cusplet is larger than the mesial one. A second, rudimentary cusplet accompanies the distal one at its base. The mesial heel is significantly elongated and marked by three very small, strongly fused cusplets. The transverse cutting edge is well developed and continuous between the cusplets and the cusp. The labial face of the crown is rather flat but cambered at the base of the main cusp. The basal margin of the labial face is concave in labial view and overhangs the root with a prominent and round bulge. Two enameloid−covered, tongue−like expansions extend ventrally and cover two of the root laminae. These expansions are more or less located in the prolongation of the notches between main cusp and first lateral cusplets. The ornamentation consists of a continuous fold reaching over the entire mesio−distal width and being more or less parallel to the cutting edge. This fold is joint by horizontally oriented, irregular and fainter ridges below the lateral heels creating a narrow band of almost reticulated ornament, which is restricted to the upper half of the crown shoulder. A short, more or less vertical, very faint fold is present in the upper third of the main cusp. Otherwise, the labial face is smooth. None of the ornamentation elements reach the basis of the tooth crown.

The lingual face is much more convex than the labial one and much less developed below the lateral heels. The ornamentation consists of four vertical, slightly irregular ridges on the main cusp and three on the first pair of lateral cusplets. The folds do not reach the base of the crown or onto the lateral heels and do not bifurcate. There are two horizontal crests below the lateral heel giving the crown shoulder an almost angular appearance in lateral view.

The root is low, rather flared laterally and arched in labial view. The angle between crown and root is about 20°. The basal face of the root is flat lingually but almost hollowed labially. Here, some irregular short but deep grooves separated by thick laminae are present on the labial face giving the root a pseudopolyaulacorhize pattern. The lingual face is broad. There is a weakly developed lingual protuberance. There are six margino−lingual foramina mesially and four distally. The medio−lingual foramen is of the same size as the margino−lingual foramina and in line with them. Some similar large foramina open labially and are continuous with the corresponding margino−lingual foramina.

The second specimen attributed to this species represents a broken−off lateral cusplet, probably from the distal part. It shows the characteristic labial and lingual ornamentation.

A single, isolated and fragmentary, bioeroded tooth crown (see below) is provisionally attributed to this species because of the distinctive crown ornamentation.

Discussion.—There has been a long dispute and controversy over the taxonomic distinction between Palaeospinax , Synechodus , and Paraorthacodus (e.g., Woodward 1889; Cappetta 1973; Herman 1977; Cappetta 1987, 1992; Thies 1991, 1992, 1993). According to Duffin and Ward (1993) Palaeospinax might be a synonym of Synechodus . Consequently previous concepts (e.g., Glickman 1957; Cappetta 1973) seem to be basically valid. Two distinct groups based on their tooth morphologies are then recognizable within palaeospinacid neoselachians: Paraorthacodus and Synechodus . The main feature of Synechodus teeth is that the lateral cusplets are not as strongly separated from the main cusp as in Paraorthacodus and that the labial face is cambered and overhangs the crown/root junction with a bulge. Because of these features, the new species from Kłęby is attributed to Synechodus . Cuny et al. (2001) erected the synechodontiform genus Mucrovenator for isolated teeth from the Middle Triassic of North America and “ Hybodus ” minor from the Late Triassic of Europe. Teeth of this genus differ mainly in the absence of the very characteristic deep grooves separated by laminae on the labial root face and a less developed bulge of the labial face. The ornamentation consists of very strong and long vertical folds. The attribution of this genus to synechodontiforms seems questionable because of the root morphology.

Synechodus is rather widespread and ranges from the Late Triassic (Rhaetian) to the Danian (Palaeocene) ( Cappetta 1987; Duffin and Ward 1993). Jurassic species are S. streitzi and S. paludinensis from the Hettangian, S. enniskilleni and S. occultidens from the Hettangian and Sinemurian, S. pinnai from the Sinemurian, S. egertonia from the Toarcian, S riegrafi from the Oxfordian and S. plicatus from the Kimmeridgian (e.g., Thies 1983; Duffin and Ward 1993; Delsate et al. 2002). Teeth of Synechodus also occur in the Bathonian (Charlie J. Underwood personal communication 2002). The anterior to lateral teeth of S. occultidens and S. paludinensis also occasionally lack vertical folds or ridges on the labial face. However, teeth of these two species differ from the new species in the presence of very weak lateral cusplets, which are absent in certain tooth files, and in the labial crown face ornament. The ornamentation is of anastomosing, reticulated pattern that is restricted to the lower parts of the crown in S. occultidens while it consists of a reticulate ornament pattern at the base of the crown and additional longitudinal, vertical ridges in S. paludinensis . The holotype of the new species resembles antero−lateral teeth of S. plicatus Underwood, 2002 to some extent. However, they are easily distinguishable on the basis of the labial enameloid prolongations in the new species. Conversely, the base of the labial crown face is straight and only slightly curved in S. plicatus .

The characteristic ornamentation and the labial enameloid prolongations distinguish the Kłęby species from all known species and allow the creation of a new species despite the small sample size. Consequently, important features such as the heterodonty of the new species could not be reconstructed. The holotype may be attributed to an antero−lateral jaw position because of the asymmetrical form.

The new record from the Callovian of Poland fills the gap between the earlier Middle and Late Jurassic occurrences of Synechodus .

An isolated tooth crown that might be attributed to the new species exhibits evidence of bioerosion by the hyphate boring Mycelites ( Fig. 3L ).

Figures

Fig. 3. A. Paratype of Folipistrix digitulus gen. et sp. nov. SMNS 87862, Weilen unter den Rinnen, SW Germany, Dogger α, lower Aalenian; in labial view, × 52. B–C. Orectolobiformes, fam. gen. et sp. indet. Weilen unter den Rinnen, SW Germany, Dogger α, lower Aalenian. B. Specimen SMNS 87863; in labial view, × 85. C. Specimen SMNS 87864; in labial view, × 115. D. Holotype of Synechodus prorogatus sp. nov. BGRX 12503, Kłęby 1/37: 244.8–245.7 m, Callovian; in labial (D1), occlusal (D2), lateral (D3), and lingual (D4) views. All × 40. E. Isolated lateral cusplet of Synechodus prorogatus sp. nov., BGR X 12504, Kłęby 1/37: 244.8–245.7 m, Callovian; in labial (E1) and lingual (E2) views. Both × 30. F. Protospinax cf. annectans Woodward, 1919. Specimen BGRX 12505, Kłęby 1/37: 244.8–245.7 m, Callovian; in labial (F 1), lateral (F2), occlusal (F3), and lingual (F4) views. All × 65. G. Protospinax cf. annectans Woodward, 1919. Specimen BGRX 12506, Kłęby 1/37: 244.8–245.7 m, Callovian; in labial (G 1), lateral (G2), occlusal (G3), and lingual (G4) views. All × 32. H. Protospinax sp. 1. BGRX 12507, Kłęby: 244.8–245.7 m, Callovian; in labial (H 1), lateral (H2), occlusal (H3), and lingual (H4) views. All × 40. J. Protospinax sp. 2. BGRX 12508, Kłęby 1/37: 244.8–245.7 m, Callovian. Labial view. K. Squalogaleus sp. BGRX 12509, Kłęby 1/37: 244.8–245.7 m, Callovian; in labial (K1), lateral (K2), occlusal (K3), and lingual (K4) views. All × 50. L. Synechodus prorogatus sp. nov.? BGRX 12510, Kłęby 1/37: 253.6–~265 m, Callovian. Labial view, × 28. M. Scyliorhinidae indet. BGRX 12511, Kłęby 1/37: 253.6–~265, Callovian; in labial view, × 14. N. Neoselachii indet. BGR X 12512, Kłęby 1/37: 253.6–~265, Callovian; in labial view, × 22.