Additional evidence as to the dentition and structure of the skull in the South African fossil reptile genus Diademodon / by H.G. Seeley.

  • Seeley, H. G. (Harry Govier), 1839-1909.
Date:
1908
Catalogue details

Licence: In copyright

Credit: Additional evidence as to the dentition and structure of the skull in the South African fossil reptile genus Diademodon / by H.G. Seeley. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    external crenulate border and a median crenulate transverse ridge, dividing the concave posterior half of the crown, which has a crenulate external margin, into larger external and smaller internal concave spaces (see text-fig. 130). In front there is a sharp or crenulate marginal border, with transverse crenulations or cusps; on the middle of the crown two small anterior cusps and two posterior cusps. These crowns are essentially of the type of the described species of Diculemodon. The last tooth of 1). mastacus shows a ten- dency to develop a posterior talon (Z. c. 1894, B, pi. 89. figs. 11,12). The penultimate tooth of this specimen has the posterior talon so developed as to make the form of the crown almost triangular. The crown is only a quarter of an inch wide, and slightly shorter from front to back externally. The strong external anterior cusp is broken, but a small external cusp rises from the talon. On the inner border of the crown are two or three cusps or crenulations like those similarly placed on the fifth and sixth molars. The last molar is compressed from side to side, inch long by j1^ inch wide, broader in front than behind, with small tubercles back and front. The small size of these teeth gives the molars the aspect of exceptional divergence posteriorly. The transverse internal measurement between the last pair of molar teeth is lyg- inch ; between the fifth pair it is f inch, and between the first pair of molars about -g- inch. From front to back the crowns form a convex err re. The dentition is imperfectly preserved, but not more than two or three premolar teeth appear to be lost. From the resemblances of the skull to allied types I infer that there was a toothless diastema between the first premolar and the canine, where the jaw contracted from side to side. I should expect four incisors as in Gomphognathus. The missing extremity of the snout would be about 1T8^- inch long ; the missing hinder part of the head was about 24 inches long, giving the complete skull a length of 6| inches. The skull may be restored on the type of Gomplio- gnathus (text-fig. 130). The most remarkable feature of the dentition is the unworn condition of the crowns of the teeth, also seen in other species of the same genus. The transversely ovate forms of the molar crowns acquire new interest from the teeth of Procolophon having this form, with inner and outer cusps recalling the tooth of Diademodon brovmi. But while Procolophon is typically I'eptilian in its dental armature (Proc. Zool. Soc. 1905, vol. i. p. 225), in this fossil the teeth suggest mammalia. The trans- versely ovate form of the crown, with the slight cingulum, approaches the condition in lemurs, but the molars are more numerous and the other dental characters unlike. The diastema occurs among mammals as various as marsupials, tapirs, rodents, but is never associated with a transversely ovate molar, and full series of incisor and strong canine teeth as in these fossil reptilian types. Mammals of various groups have the molar teeth progressively increasing and afterwards decreasing in size, as [6]