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Growth Patterns in Euconodont Crown Enamel: Implications for Life History and Mode-of-Life Reconstruction in the Earliest Vertebrates

Howard A. Armstrong and Caroline J. Smith
Proceedings: Biological Sciences
Vol. 268, No. 1469 (Apr. 22, 2001), pp. 815-820
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/3068066
Page Count: 6
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Growth Patterns in Euconodont Crown Enamel: Implications for Life History and Mode-of-Life Reconstruction in the Earliest Vertebrates
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Abstract

Euconodonts were the first vertebrates to produce a mineralized skeleton. It is concluded that the minor increments in the crown enamels of Protopanderodus varicostatus and Drepanodus robustus are probable homologues of the cross striations in hominoid enamel, although they are much more variable in thickness and represent daily to weekly growth. Major increments are superficially similar to lines of Retzuis, but represent a check in growth that is likely to have occurred at monthly intervals. Periods of above- and below-average growth are likely to have been seasonally moderated. The growth of P. varicostatus' elements are characterized by two distinct phases: the production of a triangular, asymmetrical juvenile 'proto-element' followed, in a second phase, by the development of the curved and twisted geometry of the adult element. These fundamentally different morphologies imply that juvenile and adult animals had different modes of life and/or feeding strategies. In these animals the growth of the elements was indeterminate. The growth model for euconodonts is clearly different from that of hominoid teeth as the enamel organ must have reformed repeatedly throughout life.

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