Helodus coniculus St. John and Worthen, 1866
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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-2C15-336A-FF4A-F95779537CAE |
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treatment provided by |
Felipe |
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scientific name |
Helodus coniculus St. John and Worthen, 1866 |
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Helodus coniculus St. John and Worthen, 1866
Fig. 7B–E View Fig .
Material.—Fifteen teeth.
Description.—We include in this species several isolated holocephalian teeth of different crown shapes, considering that the variety may reflect heterodonty typical of crushing−grinding dentitions. The crowns are composed of a central, bulbous structure which is relatively high, almost pointed ( Fig. 7C View Fig ), to dome−like, semi−spherical ( Fig. 7D View Fig ), to low, broad, elongated mesio−distally ( Fig. 7B View Fig ). The crowns are slightly asymmetrical. The mesial and distal branches differ in length and breadth, and slope down from the central part outwards at different angles. The whole crown is covered with a thick layer of tubular dentine, but the tubule openings in better preserved specimens are exposed on the surface only in the areas most subject to wear (see especially Fig. 7C View Fig 1 View Fig ).
The base is of a typical euselachian type, with canals and grooves on the lingual side, canal openings in the aboral−labial concavity and a broad, flat aboral−lingual surface ( Fig. 7E View Fig ).
Remarks.—Judging from such articulated specimens of basal holocephalians’ dentition as Psephodus magnus Traquair (1885 : figs. 1, 2; Ginter and Piechota 2004: fig. 3H; NMS 1950.38.51) it seems probable that the narrow and high teeth of the crushing−clutching type in Helodus coniculus ( Fig. 7C View Fig ) were situated in the anterior region of jaw. Such teeth are in fact the only ones corresponding to the type specimen ( Newberry and Worthen 1866: pl. 4: 19; see also Stahl 1999: fig. 52). The rest of teeth probably formed a crushing−grinding pavement in the lateral and posterior regions.
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