Trituberculy : a review dedicated to the late Professor Cope / by Henry Fairfield Osborn.

  • Henry Fairfield Osborn
Date:
[1897]
Catalogue details

Licence: Public Domain Mark

Credit: Trituberculy : a review dedicated to the late Professor Cope / by Henry Fairfield Osborn. 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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    made strenuous efforts to secure additional evidence, which have not thus far been successful. In the meantime too great emphasis cannot be laid upon the fact that all the existing palae- ontological evidence points in the same direction, namely, to the presence of the chief cone upon the inner side of the upper molars, and upon the outer side of the lower molars. An im- portant oversight on the part of those who are still uncon- vinced of the tritubercular theory, is the necessity of a mechan- ical adaptation of the upper to the lower teeth in every stage of development, wrhich is perfectly met by the tritubercular theory. Given the universally acknowledged trigonid or tri- angular arrangement of cusps in the lower teeth, no mechani- cal relations can be imagined in an upper molar crown which originated with the external cusps, paracone and metacone. If the main object of palaeontological research is to trace back various lines of descent as far as possible, the very unity of primitive type makes this apparently more difficult than before, but not really so. We were working before upon a false basis, or no basis at all; we can now advance upon the certain basis of primitive form and the one requisite of progress is to employ much more exact methods of description and analysis. 1. THE THREE PRIMARY FORMS. So far as the molar teeth were concerned, there were, to our present knowledge, but three great primary forms, which suc- ceeded each other as stages and also persisted. From one or other of these all the known recent or fossil mammalian teeth have diverged, including probably the Multituberculates. These types are illustrated in the accompanying cut. First, the haplodont crown, which links the mammals with the rep- tiles; second, the triconodont crown which was predominant in the Lower Jurassic period ; third, the tritubercular crown which appeared in the Lower Cretaceous1 and has been by far the most productive. The transitions between these great types 1 It now appears advisable that the so-called Como (Atlantosaurus) Beds of North America and the Purbeck Beds of England should be placed in the base of the Cretaceous instead of in the Upper Jurassic as formerly.
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