Cladodus thomasi Turner, 1982
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publication ID |
https://doi.org/ 10.26879/583 |
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persistent identifier |
https://treatment.plazi.org/id/ED189025-6064-FF88-FC5C-FEE66B3E9700 |
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treatment provided by |
Felipe |
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scientific name |
Cladodus thomasi Turner, 1982 |
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Figure 4.1-7 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7
v. 1959 “Cladodont”; Thomas, p. 36, fig. 4a.
v. 1982 Cladodus thomasi sp. nov.; Turner, pp. 125, 127, figs. 6C, 7J.
Material. Four teeth from sample 198404, two teeth from sample 198480, eight teeth from TS-1, Laurel Formation, Laurel Downs, Tournaisian.
Revised diagnosis. Teeth with nine cusps; a large central cusp, a pair of large lateral cusps and three smaller pairs of intermediate cusplets ( Figure 4.1- 4 View FIGURE 4 ). The central cusp is the largest followed by the outer cusps, which diverge in a slight distal direction. The first and third lateral cusps are small, approximately a quarter to one-third the size of the lateral cusps ( Figure 4.5 View FIGURE 4 ). The second pair of intermediate cusplets are almost equal in size to the outer lateral cusps. Converging ridges are present on the base of the main cusp ( Figure 4.7 View FIGURE 4 ) whereas the lateral cusps all bear strong, non-bifurcating ridges ( Figure 4.6-7 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 ). The central cusp bears a slight depression along the baso-labial face and is rounded along the lingual face. A secondary row of small labial cusplets is present on the crown base of larger teeth ( Figure 4.6-7 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 ). The basal outline is lozenge shaped in smaller teeth ( Figure 4.2 View FIGURE 4 ) becoming trapezoid in larger specimens ( Figure 4.6 View FIGURE 4 ). An elongate oro-lingual button bearing four canal openings abuts the lingual margin. Small foramina accompany the pore canals on the lingual and the occlusal surface of the oro-lingual button. A row of small foramina also occur within an arched groove on the labial surface immediately below the crown-base interface ( Figure 4.4, 4.7 View FIGURE 4 ). A baso-labial shelf extends between the first set of lateral cusplets and is slightly thickened at the distal edges ( Figure 4.4, 4.7 View FIGURE 4 ). A shallow depression is present on the labial underside of the base, which also bears multiple canal openings. The lingual portion of the base is flattened under the oro-lingual button but may be flared occlusally along the distal edges of the lingual margin ( Figure 4.1, 4.3 View FIGURE 4 ).
Description. Teeth range in size from 2.2 mm to 90 mm in length, mesio-distally. The crown includes a prominent triangular central cusp, which is flattened to depressed along the labial margin and convex along the lingual face ( Figure 4.6 View FIGURE 4 ). A pair of lateral cusps and three pairs of intermediate cusplets flank both sides of the medial cusp. The outermost cusps are the largest and approximately one quarter larger than the second lateral cusplets. The first and third pairs of intermediate cusplets are of smaller size, ranging from a quarter to half the size of the lateral cusps ( Figure 4.3, 4.5 View FIGURE 4 ). Prominent, non-bifurcating ridges are present on both the labial and lingual faces of each lateral cusp. Larger specimens ( Figure 4.6-7 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 ) show a small row of cusplets along the baso-labial face of the crown. Small teeth show a more lenticular outline to the base ( Figure 4.2 View FIGURE 4 ). A roughly trapezoid basal outline with rounded edges ( Figure 4.6 View FIGURE 4 ) is present in larger specimens. An elongate ovoid button, extending between the inner margins of the second pair of lateral cusps, is positioned close to the lingual rim and is perforated by four canal openings on the lingual face. A small baso-labial shelf, between the first lateral cusps, borders an often weakly developed baso-labial depression below the central cusp ( Figure 4.4 View FIGURE 4 ).
Remarks. The original diagnosis of Cladodus thomasi Turner, 1982 was based on a small tooth from the Upper Bundock Formation, Queensland (Holotype UQG F73007) as well as a tooth partially obscured by matrix ( Thomas, 1959, figure 4a) collected from the Laurel Formation in the vicinity of Twelve Mile Bore ( Figure 1). The teeth recovered here, also collected from the Laurel Formation, conform to the original diagnosis for this species in addition to providing further diagnostic characters which allow for these teeth to be reassigned to the genus Cladodus . The central cusp morphology of C. thomasi , with its flattened labial face and convex lingual surface ( Figure 4.6 View FIGURE 4 ), is quite different to the biconvex cusp-type in Stethacanthus . Cladodus thomasi is further differentiated from Stethacanthus by multiple intermediate cusps. The baso-labial shelf and elongate oro-lingual ridge, typical of the genus Cladodus , are also found in C. thomasi .
The new specimens of C. thomasi from the Canning Basin have highlighted previously undescribed variation in tooth morphology. Differences are typically seen in the basal outline with smaller teeth possessing a more lozenge shaped outline that becomes more trapezoid in form as the size of the tooth increases. Further variation is present in some of the larger teeth ( Figure 4.6-7 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 ) which bear a second small row of labial cusplets. These accessory cusplet rows are also found in other Carboniferous ctenacanthiform teeth such as Tamiobatis vetustus Eastman, 1897 ( Williams, 1998, figure 5A-B) and Saivodus striatus Agassiz, 1843 (Ginter et al., 2010, figure 72A-B).
Several Famennian cladodont teeth, possessing a single intermediate cusplet, were previously attributed to “ Stethacanthus” thomasi ( Derycke, 1992, plate 2:10-11; Hampe, 2000, plate 2:1-4). Given the morphological variation and large number of teeth, it is clear the teeth of C. thomasi possess three sets of intermediate cusplets, independent of the tooth size. This suggests the teeth figured in Derycke (1992) and Hampe (2000) are unlikely those of C. thomasi but instead belong to another ctenacanthiform shark. The tooth (MCD 177) formally figured by Derycke (1992, figure 14, plate 2: 10, 11) was synonymised firstly with Stethacanthus resistens Ginter, 2002 and then with Cladodoides wildungensis by Ginter et al., (2010), who also suggested many of the teeth formally attributed to “ Stethacanthus thomasi ” belong to C. wildungensis .
Cladodus thomasi was considered as a junior synonym of Stethacanthus obtusus Trautschold, 1874 by Lebedev (1996); however, Hampe (2000) noted S. obtusus had a greater number of cusps than C. thomasi in addition to more foramina along the edge of a less distinguished button and therefore the species determination of S. thomasi was retained. The holotype of C. thomasi ( Turner, 1982, figure 6C) is an asymmetric tooth possessing eight cusps. The newly recovered teeth of C. thomasi indicate the possession of nine cusps is common for these teeth, similar to S. obtusus . The lingual button appears more developed in C. thomasi , as noted by Hampe (2000) and typically possesses four large foramina on the lingual face. In comparison, S. obtusus is described as possessing two to six large foramina. The larger forms of C. thomasi , comparable in size to S. obtusus figured by Lebedev (1996), possess a distinct secondary row of cusplets along the labial face of the tooth, a feature lacking in the 40 specimens of S. obtusus . Further distinguishing C. thomasi from the Canning Basin is the shape of the base, which takes on a more trapezoid form in larger specimens compared to the lozenge shape seen in S. obtusus . The baso-labial shelf is also more elongate in S. obtusus , than C. thomasi , extending to the medial cusplets. In C. thomasi the baso-labial shelf only extends between the distal margins of the first pair of intermediate cusplets. We believe these differences are sufficient for C. thomasi to be retained as a distinct species.
We note there are similarities between the teeth, designated here as C. thomasi and Tamiobatis sp. ( Ginter and Sun, 2007) from Muhua, south China, including the presence of three pairs of intermediate lateral cusplets, that alternate in height, as well as a basal outline, which extends lingually furthest in front of the lingual button. However, the teeth from the Canning Basin are distinct in that they lack a small lateral cusplet often present in the teeth from Muhua and have a far more angular basal outline. The teeth of Tamiobatis sp. ( Ginter and Sun, 2007) also lack the row of accessory labial cusplets despite being of comparable size to the teeth of C. thomasi . Another member of the genus, Tamiobatis vetustus Eastman, 1897 ( Williams, 1998), is known for the presence of labial cusplets, however they are present behind the main cusp, a feature not found in the teeth of C. thomasi ( Figure 4.7 View FIGURE 4 ). Although there are some features of the genus Tamiobatis , which are present in the teeth of C. thomasi , the greater number of morphological differences precludes these teeth from being assigned to Tamiobatis .
Distribution and stratigraphic range. Given the revised diagnosis, C. thomasi is restricted to the Lower Carboniferous of Australia. Teeth have been recovered from the Lower Carboniferous upper Bundock Formation, North Queensland and from the Tournaisian Laurel Formation, Canning Basin, Western Australia.
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