Abstract

The 500–2000 m thick Early Devonian Upper Gaspé Limestones of the Gaspé Peninsula, Quebec, were deposited in moderately deep water, below wave base. The brachiopod–trilobite–dominated faunas lived during the long interval of community stasis that has been termed ecologic–evolutionary unit (EEU) VI. Synecologic analysis of these faunas by Q-mode cluster analysis produced 10 distinct brachiopod-dominated faunal assemblages (FA's). Most of these can be assigned to previously recognized communities or community sequences. An eleventh FA, artificially recognized, is dominated by trilobites, and it includes a newly recognized Roncellia gaspensis Community. Synecologic changes during the interval under investigation were gradual. FA's either extended through most of the interval or were derived directly from previous FA's. This evolutionary pattern probably represents evolutionary fine tuning, such as is expected during the long intervals of EEU stasis. Even though most of the Phanerozoic is composed of these intervals of EEU stasis, few studies have examined these intervals. Most synecologic work has concentrated on either intervals of reorganization of EEU's or times when the local environments caused changes in the local community composition. This study of a uniform habitat during an interval of EEU stasis serves to document the background rates of synecologic change and could serve as a standard against which the times of more dramatic synecologic reorganization can be compared.

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