On Pareiasaurus bombidens (Owen), and the significance of its affinities to amphibians, reptiles, and mammals / by H.G. Seeley.

  • Harry Govier Seeley
Date:
1888
Catalogue details

Licence: Public Domain Mark

Credit: On Pareiasaurus bombidens (Owen), and the significance of its affinities to amphibians, reptiles, and mammals / 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.

    18/76 page 74
    P. bombidens* None are well enough preserved to show whether the extremities of the crowns of the teeth were similarly serrated. The external enamelled surface is similarly semi-ovate and rounded from front to back, but in several instances it is marked by a few slight vertical ridges. The bases of the crowns are nearly circular; each is about 1 centim. long and rather wider, with a large central pulp cavity which extends above the alveolar margin. The interspaces between the bases of the crowns are about 2 to 3 millims. long, but the summits of the crowns, which become com- pressed from within outward, are apparently in contact. Some of the crowns are from 2 to 2 '5 centimetres long. In the lower jaw the teeth are directed more or less outward, but this is more obviously an accident of fossilisation than the inward direction of the teeth in the skull. The crowns of the teeth are vertically ribbed. The external alveolar margin rises higher than the internal margin. No evidence has been adduced as yet concerning the relation of the teeth to the jaw, though Sir It. Owen compares it to the condition seen in Iguanodon. In Iguanodon the teeth are essentially in an alveolar groove, though on its internal surface there are vertical grooves for the teeth, which terminate at their bases in separate pits. The only material available for settling this question is the small fragment of the lower jaw of Pareiasaurus serridens which appears to have been cut from the head of the specimen which Mr. Bain presented to the Geological Society in 1838. Dr. Woodward, F.B.S., has had the kindness to have this specimen cut vertically through the interspace between two teeth, and this section shows the existence of a bony septum between the teeth, thus demonstrating that the teeth are implanted in sockets (Plate 16, %• 2)- The vertical section figured by Sir B, Owen is remarkable for showing a successional tooth beneath a crown without any fang. The fang is present, however, in the succes- sional tooth, and closed at its base ; but the union between the crown and fang appears to have been of the kind seen in Mosasaurus. From the position of the successional tooth, interior to the tooth in use, it is probable that it was developed as in Ichthyo- saurus, Crocodilus, &c., so as to be more and more within the fang of the pre-existing tooth as its growth increased ; only in this case there is no trace of a fang to the tooth in use, from which it would follow that in the process of fossilisation the fang of the pre-existing tooth disappeared, while the fang of the successional tooth remained; or else, as I think more probable, that the fang of the old tooth was absorbed before the new tooth was fully grown, and that meanwhile the crown was held in its place in the jaw by a deposit of osseous cement, in which case the condition of dentition would make a transition between that of Protorosaurus and the Crocodiles. * ‘ Catalogue of Fossil Reptilia of South Africa,’ Plate 8, fig. 3.
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