Tamiobatis sp.
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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-2C1C-3360-FF80-F84E79F978AB |
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treatment provided by |
Felipe |
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scientific name |
Tamiobatis sp. |
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Fig. 3D–G View Fig .
Material.—Twenty five teeth.
Description.—Most specimens tentatively attributed here to Tamiobatis are in a very poor state of preservation. Crowns of all the teeth but one are completely devoid of enameloid and external layers of dentine; bases seem to be largely dissolved. Therefore, restoration of the real shape of these teeth and their classification is rather problematic.
It is evident that the crown is of cladodont design, with numerous lateral cusps. The best−preserved crown ( Fig. 3F View Fig ) is composed of a prominent, but relatively low median cusp and ten lateral cusps. On each side of the median cusp there are two larger cusps, two intermediate cusplets and an accessory cusplet in the outermost position. The median cusp, considerably compressed labio−lingually, is twice as high and three times as broad at the base as the highest lateral cusps and bears a few, rather coarse cristae on both faces and a lateral carina. Similar ornamentation apparently occurs on the largest lateral cusps. Most other teeth possess smaller number of lateral cusps, but the general pattern: smaller−largersmaller cusplet is always present. Also in the majority of specimens (except Fig. 3D View Fig ) the largest lateral cusp is flanked by the outermost accessory cusplet.
The base is short, laterally elongated, probably with typical ctenacanthoid articulation devices: laterally elongated, ridge−like button ( Fig. 3D View Fig 1 View Fig ) and a shelf−like basolabial projection wider than the base of the median cusp ( Fig. 3E View Fig ).
Remarks.—In the overall appearance and size, these teeth strongly resemble those of specimen CMNH 9280, Tamiobatis vetustus sensu Williams (1998) from the upper Famennian Cleveland Shale of Ohio. However, they clearly differ by the lack of a row of minute labial accessory cusplets, so characteristic of the referred specimen. Teeth of T. wachsmuthi (St. John and Worthen, 1875) from the Kinderhookian of Iowa lack such accessory cusplets ( Fig. 10D View Fig ), but they are about three times larger than the largest teeth of Tamiobatis sp. from Muhua and their median cusp is ornamented only at the base.
It must be noted here that the classification of T. wachsmuthi and certain other cladodonts such as T. succinctus (St. John and Worthen, 1875) , and, consequently, the specimens from Muhua, ascribed to the genus Tamiobatis is based solely on the close resemblance (observed by Williams 1998) between the skulls of the partially articulated, tooth−bearing specimen CMNH 9280 and the type specimen of T. vetustus Eastman, 1897 (NMNH 1717, only neurocranium). Not all the authors agree with Williams’ conclusions (see Maisey 2005).
Ctenacanthiformes gen. et sp. indet.
Fig. 9F View Fig .
Material.—One tooth.
Description.—The only known tooth of this probably yet undescribed shark is a moderately large cladodont (width of base 14 mm, height at the median cusp 7.5 mm, originally possibly about 10 mm) with three lateral cusps on each side of the prominent median cusp. The second pair of lateral
GINTER AND SUN—EARLY CARBONIFEROUS CHONDRICHTHYANS FROM CHINA 711
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cusps is the highest. The segments of the base below the median cusp and that below of the main lateral cusps are in line, but the intermediate and outermost cusplets are placed more labially ( Fig. 9F View Fig 2 View Fig ). There is a trace of a minute accessory denticle at the base of one of the intermediate cusplets ( Fig. 9F View Fig 3 View Fig ). The labial face of all the cusps is ornamented by a few vertical cristae; on the median cusp, they probably do not reach the tip. The lingual face seems to be completely smooth, but as the lingual part of the base is broken ( Fig. 9F View Fig 1 View Fig ), this may be a result of post−mortem abrasion.
The complete shape of the base is unknown, but the wavy outline of the labial rim is fairly well preserved. There is a basolabial depression below the median cusp and two rounded prominences, situated below the intermediate cusplets, are framing it. On the aboral side of the base, there probably were two rounded projections ( Fig. 9F View Fig 4), similar to those observed in the Pennsylvanian ctenacanthid Glikmanius occidentalis (Leidy, 1859) , but in the specimen from Muhua these are preserved only as vague swellings.
Remarks.—Hitherto, no other shark teeth presenting all of the above−mentioned features have been recorded. The teeth of Glikmanius do have a deep basolabial depression, two basolabial prominences and labially produced intermediate cusplets, but the outermost pair of smaller accessory cusplets is absent. Such cusplets are typical of Tamiobatis , but the latter has a generally straight basolabial rim and multiple intermediate cusplets of variable height (see above).
The tooth closest in its characteristics to the specimen described here was found among the dentition of a lower Viséan shark recently found in Glencartholm, Scotland (NMS 2000.14.2; Fig. 10F View Fig ). That very large tooth (base width about 40 mm) possesses an outermost pair of accessory cusplets placed similarly to the cladodont from Muhua and displays similar proportions between the cusps. However, it has a shelf−like basolabial projection (as in Ctenacanthus , see Williams 2001) instead of two separate prominences, its basolabial depression is shallow, and all the cusps appear to be positioned more in line than in the Chinese specimen.
It is worth noting here that the Scottish shark may represent a well known ctenacanthiform species, Goodrichthys eskdalensis (Moy−Thomas, 1936) . The holotype of Goodrichthys , also from the Viséan of Glencartholm, has damaged teeth, but careful comparison of the available fragments with the teeth exposed in NMS 2000.14.2 reveals several common features ( Ginter 2007). We therefore tentatively suggest that morphologically, the tooth under study occupies an intermediate position between Goodrichthys and Glikmanius and can arguably be attributed to the Ctenacanthiformes .
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