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Shell Microstructure of a Middle Devonian (Hamilton Group) Bivalve Fauna from Central New York

Joseph Gaylord Carter and Michael J. S. Tevesz
Journal of Paleontology
Vol. 52, No. 4 (Jul., 1978), pp. 859-880
Stable URL: http://www.jstor.org/stable/1303906
Page Count: 22
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Shell Microstructure of a Middle Devonian (Hamilton Group) Bivalve Fauna from Central New York
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Abstract

The Marcellus and Skaneateles Formations of central New York contain the earliest molluscan faunas known with excellent preservation of original calcitic, relict aragonitic and relict periostracal microstructures. Data from the Bivalvia from this fauna near Morrisville, New York, show that the Middle Devonian Nuculacea, Ambonychiacea and Pteriacea were nacroprismatic, like their later representatives. In contrast, the Nuculanacea show nacreous structure combined with crossed lamellar, complex crossed lamellar, or homogeneous structure, or simply complex crossed lamellar and homogeneous structure. These data are compatible with the hypothesis that the nacroprismatic microstructure grade is primitive in the subclasses Palaeotaxodonta and Pteriomorphia. The pterineid Ptychopteria (Cornellites) fasciculata differs from other Middle Devonian Pteriacea in its lack of an outer simple prismatic layer in the more convex (left) valve. This produced rigidity in the left valve margin, resulting in a pectinoid-grade shell microstructure. Evidence of discrete spikelike calcification within the periostracum of Modiomorpha concentrica is compatible with the hypothesis that the Modiomorphacea and Mytilacea are closely related. Like the modern Mytilacea, the Middle Devonian Modiomorphacea are microstructurally variable, and often combine nacreous and complex crossed lamellar structures in the same shell.

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