Cassisodus margaritae, Ginter & Sun, 2007
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publication ID |
https://doi.org/ 10.5281/zenodo.13741212 |
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persistent identifier |
https://treatment.plazi.org/id/954A87EC-2C11-336E-FC8C-F90A7E547FD0 |
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treatment provided by |
Felipe |
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scientific name |
Cassisodus margaritae |
| status |
sp. nov. |
Cassisodus margaritae sp. nov.
Fig. 5 View Fig .
1996 Lissodus sp. ; Ivanov 1996: fig. 7A, B.
Holotype: Specimen PKUM02−0145 ( Fig. 5A View Fig ) from the MH section north of Muhua , Guizhou Province, southern China; sample MH−1, bioclastic limestone, Carboniferous , Mississippian, Tournaisian, Siphonodella crenulata conodont Zone.
Derivation of the name: Latin margarita = pearl, a girl’s name.
Material.—Four teeth.
Diagnosis.—As for genus.
Description.—As in the case of other euselachian and euchondrocephalan sharks’ teeth in the collection, a considerable degree of heterodonty is observed in the dentition of Cassisodus margaritae sp. nov. Fortunately, in this case the characteristic distribution of accessory labial and lingual cusplets on the lateral cusps makes the identification easier. Among the four teeth assigned here to this species, there is one ( Fig. 5A View Fig ) rather narrow (2 mm mesio−distally), very well preserved tooth, possibly representing anterior, clutching part of the dentition, and three wider (up to 4 mm mesio−distally), crushing, partly damaged lateral(?) teeth ( Fig. 5B–D View Fig ).
The width/length (mesio−distal/labio−lingual) ratio of the first tooth (holotype, Fig. 5A View Fig ) is about 2. The size of the median cusp is roughly double that of the lateral cusps. The lateral cusps are closely packed and their mesio−distal compression is stronger than in the other specimens. Each lateral cusp forms a group with one labial accessory cusp and up to two cusplets on the lingual side. The accessory cusplets are connected with the tips of lateral cusps by labio−lingual carinas. Similar carinas may connect accessory cusplets of the adjacent groups ( Fig. 5A View Fig 3 View Fig , A 6 View Fig , right side). There are four accessory cusplets at the base of the lingual side of the median cusp, symmetrically placed towards the midline, and a single cusplet on the labial side. The lingual part of the base is relatively extensive. It seems to be narrower than the crown, but this is probably an illusion, caused by the fragments broken off symmetrically. In the aboral view, the labial, porous and the lingual, smooth, parts are distinctly separated.
The other three, wider teeth ( Fig. 5B–D View Fig ; original width/ length ratio about 3.5) are partly broken and their crowns appear to be polished, either by wear or by post−mortem abrasion. They are so similar to each other, save for the size, that we suspect they come from the same tooth family. The smallest of them ( Fig. 5B View Fig ) is in the best shape. The median cusp is only twice as large as the nearest lateral cusps. The lateral cusps are more widely spaced and the labial accessory cusplets, apparently not belonging to any cusp+cusplets group, occur between them ( Fig. 5B View Fig 1 View Fig ). There are at least three groups of cusplets on each side. The lateral ends of the tooth are very narrow, almost pointed.
Remarks.— Cassisodus margaritae sp. nov. shares several general features with basal holocephalians, such as Helodus : shape and vascularisation of the base (euselachian−type), and differentiation of teeth (anterior narrower with high median part, posterior very wide with lower crowns). However, it differs clearly by the lack of tubular dentine (orthotrabeculine sensu Zangerl et al. 1993) and by having developed instead a very sophisticated ornamentation. Owing to these differences, it more closely resembles Famennian forms such as Deihim Ginter, Hairapetian, and Klug, 2002 , which is also a supposedly highly heterodont taxon. As mentioned in the diagnosis, the strong labial overhang of the crown, supported by the accessory cusplet, makes the teeth of C. margaritae look like those of Lissodus . Stratigraphic and geographic range.—Middle Tournaisian of southern China (Muhua), Viséan of southern Urals (Sikaza).
Hybodontoidea gen. et sp. indet.
Fig. 6A View Fig .
Material.—One complete tooth and one crown.
Description.—The crown of the complete tooth is composed of three largely fused cusps, of which the median, pyramidal in shape, is the highest. The crown is provided with a prominent labial peg, similar to that of Lissodus . On the lingual face of each lateral cusp there is a strong vertical ridge, widening downwards. A similar, bifurcating ridge is also present on the lingual face of the median cusp.
The most remarkable feature of this tooth is its very deep (twice as deep as the crown height), subrectangular base, slightly directed linguad. It is generally of the euselachian type, with a spongy structure.
Euselachii gen. et sp. indet.
Fig. 6D View Fig .
Material.—One complete tooth and two fragments.
Description.—The well preserved tooth is relatively large (base width above 6 mm), with a thick euselachian−type base and a virtually symmetrical crown of the shape intermediate between cladodont and protacrodont. Altogether, there are nine cusps in the crown, standing upright in the lateral view. The prominent median cusp is pyramidal, showing protacrodontlike, coarse cristae (also present in the lateral cusps), but its relative height is greater than that in typical protacrodonts. Of the lateral cusps, the outermost are the largest and divergent from the midline, these two features distinguishing them from typical hybodonts (see Agassiz 1833 −43: vol. 3: 178). The intermediate cusplets are largely fused, at least up to two thirds of their height. The middle of the three is the highest.
Remarks.—The intermediate morphology of the crown combined with the euselachian base as well as the lack of comparable specimens in the literature preclude any definitive classification of these teeth at the moment. In fact, there are many similar, unnamed cladodont−protacrodont teeth dispersed in the Palaeozoic collections all over the world. It is probable that the taxa to which they belonged are situated close to the point of ctenacanthiform−euselachian divergence.
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