Literaturdatenbank
Literaturdatenbank |
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Newman, H. H. (1906). The significance of scute and plate "abnormalities" in chelonia. Biological Bulletin, 10, 99–114.
Added by: Sarina Wunderlich (24 May 2009 21:32:41 UTC) |
| Resource type: Journal Article BibTeX citation key: Newman1906 View all bibliographic details  |
Categories: General Keywords: Chelydra, Chelydra serpentina, Chelydridae, Chrysemys, Chrysemys picta, Emydidae, Graptemys, Graptemys geographica, Schildkröten = turtles + tortoises, Systematik = taxonomy Creators: Newman Collection: Biological Bulletin |
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| Abstract |
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Graptemys geographica Chrysemys picta Chelydra serpentina Palæontological and embryological evidence is at variance as to the origin and character of the neural and costal plates, but observations point strongly to a periosteal origin of these structures, which means that they are in no sense dermal or the descendants of the original dermal carapace. The testimony of comparative anatomy leads to the belief that the nuchal, procaudal, pygal and marginal plates are the remnants of a once more or less complete dermal carapace and that these plates formed the cores of scutes that must have had a more or less tubercular form. The keels of existing scutes represent these tubercules. The testimony of the tail-trunk of Chelydra indicates that there were originally seven primary rows of such scutes and that less prominent rows of scutes occupied the interspaces. These less prominent rows were gradually suppressed, first on the carapace and then on the plastron, beginning in the middle and proceeding laterally. Thus the first loss was the neuro-costal rows, second the supra-marginals, third the interplastrals, and fourth the inframarginals, which to-day persists normally in many. primitive forms. Accompanying the suppression of rows occurred a reduction in the number of scutes in the primary rows, and this reduction took a general antero-posterior direction. At the same time the rapid secondary growth of the neural spines and ribs caused the suppression of the corresponding dermal plates, leaving only the nuchal, procaudals, pygal and marginals in places where the internal skeletal portions failed to extend. Traces of the dermal armor in the mid-neural region have been found, however, in Toxochelys and Graptemys. No correlation of abnormalities is to be expected in the neural and costal regions, since the scutes and plates of this region are entirely independent in origin, but in the marginal series, where the plates and scutes retain nearly their original connections, the correlation is perfect. In the procaudal region we find frequent correlations, but, that the correlation is not a necessary one, is shown by numerous uncorrelated abnormalities. A study of the color-markings of Graptemys and Chelydra lends confirmation to all the above theories of the chelonian carapace and plastron, and at the same time serves to rationalize the patterns themselves.
Added by: Sarina Wunderlich |