Abstract

The morphology and development of protaspides representing the family Asaphidae are described from silicified specimens etched from Middle Ordovician limestones of northern Virginia. Close similarities with remopleuridid protaspides described by Whittington and Ross suggest that the Asaphidae and Remopleurididae are more closely related than generally has been recognized. The asaphid protaspides represent early stages of the protaspid period, before complete differentiation of a protopygidium. For an unknown reason, the late protaspid period is not represented among the fossils, although early meraspid stages are common. The resultant "missing" interval in the recorded asaphid ontogeny appears to be the interval best represented by known remopleuridid protaspides. Evidence for and some implications of this interpretation are discussed.

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