Labyrinthodont tooth from South Africa / by H.G. Seeley.

  • Harry Govier Seeley
Date:
1908
Catalogue details

Licence: In copyright

Credit: Labyrinthodont tooth from South Africa / 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.

    6/8 page 242
    the lower part of the crown, where the number of ribs is greater. They do not often show dichotomous division ; hut the ribs which, rise from the base irregularly die away in the grooves. They have an appearance of being finer and more numerous in the lower part of the crown than at the transverse fracture, where they number about eighty. There is practically no enamel on the crown, which shows only a faint surface gloss. On receiving the tooth I had a cast made, and a transverse section was prepared so as to show the labyrinthic structure of the crown. The cut surface now has the appearance of being bordered at the circumference by close-set tubes which correspond to the external vertical ribs. Under the microscope these sections of the reed-like sheath of the tooth are mostly sub-quadrate, and hollow; separated from each other by a narrow band which passes inward and folds into the labyrinthic substance of the tooth. The centre of the crown of the tooth is occupied by the pulp cavity, nearly circular, slightly longer than wide; with a number of fine films at irregular intervals, radiating outward from it as vertical plates dividing the folded tooth substance. The folding of the dentine is more complicated than in any genus yet examined. Counting from the inner border there are about twenty-five folded labyrinthic plates of dentine, which radiate to the circumference, without greatly varying in width. Each of these plates is made up of twelve or more alternate folds to right and left of the tooth substance, with each fold often plicated, and including spaces more or less small, frequently ovate, sometimes more elongated. The dentine is composed of tubes which show a radiating arrangement in harmony with the curvature of the folds. Each layer bears a thin film upon its external infolded surface which appears to correspond in position to enamel. This layer passes outward between the folds of dentine, and appears to extend over the external surface of the tooth, though most of the enamel is manifestly lost. Between the folded plates are a series of supplementary wedge-shaped folds, about half as numerous, which are continuous with the dentine of the plates on each side, sometimes by its being folded over on the one side, and connected by anastomosis on the other side. The most distinctive features of the tooth are: (1) the external layer of vertical tubes of dentine ; (2) the denseness of the folding of the dentine ; (3) the connection of the folds with each other in ways different to those known in Mastodonsaurus; and (4) the number of small vacuities included in the folds of the dentine. The only clue to the form of the skull is given by the small palatal vacuity, presumably palato-nasal, which descends upon the base of the tooth, and may be evidence that the skull was broad, depressed convex in front, with the nares in a forward position. The only genus with the skull of this type hitherto indicated is the imperfectly known Batrachiosuchus of Dr. it. Broom ; but that type is far too small to have carried teeth of this size, which may indicate a skull twice as large, or about 18 inches long. The teeth in Batrachiosuchus are undescribed. I do not anticipate that it will prove referable to Ptychosphenodon (Geol. Mag., 1907, Dec. Y, Yol. 1Y, p. 433), but it is from an animal equally large.
    digitised image 1
    digitised image 2
    digitised image 3