Chondrenchelys Traquair, 1888
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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-2C14-3377-FCDA-FA807EE57FCA |
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treatment provided by |
Felipe |
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scientific name |
Chondrenchelys Traquair, 1888 |
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Genus Chondrenchelys Traquair, 1888 Chondrenchelys sp.
Figs. 8E View Fig , 9A, B View Fig .
Material.—Three tooth−plates.
Description.—There are tooth plates of two kinds in the studied material: one large plate, elongated antero−posteriorly ( Fig. 9A View Fig ), and two smaller, triangular plates ( Figs. 8E View Fig , 9B View Fig ); one of the latter is partly destroyed. All the plates have smooth, concave aboral surfaces and wavy oral surfaces, ornamented with concentric ridges separated by areas with numerous minute pores.
On the larger plate, the centre of the ridges is situated in the anterolabial region (identification of sides is based on articulated specimens of Chondrenchelys problematica Traquair, 1888 , from Scotland; Fig. 8A, B View Fig ). The primary ridges are more densely packed anteriorly. Posteriorly, the spaces between them become so wide that in a few instances secondary ridges are added. Thus, in the anterior part there are 13 ridges and posteriorly their number increases to 17. There is a major sella in the middle of the plate, directed anterolabio−posterolingually, framed by two sinuses. The anterior and posterolabial margins of the oral surface are upturned.
On the smaller plates, the growth centre is probably placed posterolabially (in this case the sides are identified based on Harpagofututor volsellorhinus Lund, 1982 , a chondrenchelyid from Montana). There are about 14 ridges in the posterior part and two to three added at the anterior corner. The oral surface is gently concave, with the posterior and anterolabial margins upturned .
Remarks.—The larger tooth plate is very similar to the posterior plates of Chondrenchelys problematica from the lower Viséan of Glencartholm, Dumfriesshire, Scotland, but it is impossible to decide at the moment, whether it represents an upper or lower pair (compare Fig. 8B View Fig ). The smaller plates are probably anteriors. Unfortunately, none of the specimens of Chondrenchelys examined by Lund (1982: text−figs. 4D, 5F) and by us showed the oral view of anterior plates, so the comparison is problematic in this case. The outline of the smaller plates from Muhua is comparable to the anterior plates of H. volsellorhinus from the Serpukhovian of Bear Gulch in Montana ( Lund 1982: pl. 2: 4, 5), but their ornamentation (radiating ridges with coarse nodes in Harpagofututor ) is different. Interestingly, the sculpture of the posterior plates in H. volsellorhinus and that of Chinese material is almost identical (compare Fig. 8D and E View Fig ). On the other hand, the plates of C. problematica do not show pores between ridges. This may be only a matter of preservation, because the tubules in tubular dentine are originally covered by a thin outer mineral layer (pallial dentine), often partly or completely removed during fossilisation. Nevertheless, because of this difference and inability to compare anterior tooth plates, we leave our material in open nomenclature.
Chondrenchelyidae gen. et sp. indet.
Fig. 9C View Fig .
Material.—Two teeth of a tooth−file.
Description.—The crowns of the teeth are rectangular with rounded corners, convex, each resembling a loaf of bread in oral view. The surface is ornamented with concentric ridges whose growth centre is situated labially. Spaces between the ridges are perforated with numerous pores, similarly to the tooth plates of Chondrenchelys sp. The bases are of the euselachian type, thick, with a broad basolingual surface devoid of foramina. The tooth bases are overlapping, clearly showing the mode of attachment between the teeth in a tooth family. Although the basolingual surface of the more lingual tooth is damaged, it is evident that these surfaces in subsequent teeth formed together a uniform, concave, almost completely smooth surface.
Remarks.—Assignment of this specimen to the Chondrenchelyidae is provisional and based only on the similarity of ornamentation of occlusal surfaces. Thus far nothing alike was recorded from the members of this family. However, this type of dentition could represent an intermediate, basal form of the group in which not all the teeth have been transformed into tooth plates, but are already strongly attached to each other. These loaf−like teeth resemble the flat teeth in Psephodus magnus ( Traquair 1885: figs. 1, 2), which coexist in the same dentition with narrow, Helodus −like teeth on one side and broad, sturdy tooth plates on the other. However, because of their size it is unlikely that the teeth under description could occur together with the plates of Chondrenchelys sp.
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