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

  • Osborn, Henry Fairfield, 1857-1935.
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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    are found among the Mesozoic mammalia and have already be m worked out with considerable care. From each of these great primary stages it would at first appear that some of the mammalia directly derived their den- tal type, for both the “ haplodont ” and “ triconodont ” crowns are seen to-day among the Cetacea. Yet there is ground for uncertainty here, for as the progressive stages are “ haplodont,” “ triconodont,” “ tritubercular,” so the retrogressive stages re- verse this order, passing from “ tritubercular ” back to “ tri- conodont ” then into “ haplodont.” Another view therefore is that such primary forms have been secondarily acquired. The apparently “ triconodont ” lower molar of Thylacinus is, for example, an indirect retrogression from a tritubercular ancestral form. Again, among the aquatic carnivora, in the series of molars of the Seals, the eared Seals and the Walruses, we see the backward stages from the “ triconodont ” to the “ haplodont; ” and it is therefore probable that the “ trituber- cular ” was the form of molar possessed by the Pinnipedia when they diverged from the Fissipedia. There is consider- able evidence that a similar retrogression has simplified the Fig. 5.—Amphilestes, a Jurassic triconodont, primary. molar crowns of modern Edentates, for it is now certain that at least the Gravigrada were descended from tritubercular ances- tors, the Ganodonta. Again, among the Cetacea, all their oldest allies, such as Zeuglodon, are triconodont, not haplodont. With both these groups, therefore, there are therefore the possi- bilities of direct or of retrogressive origin of the “ triconodont ” molar. This uncertainty hardly extends to the “ triconodont ” stage, which is typically shown in the lower Jurassic Amphilestes,