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Journal of Paleontology

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PALEOECOLOGICAL AND PHYLOGENETIC IMPLICATIONS OF ASEXUAL REPRODUCTION IN THE PERMIAN SCLERACTINIAMORPH NUMIDIAPHYLLUM

¹ Department of Geosciences, Osaka City University, Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan, <ezaki{at}sci.osaka-cu.ac.jp>

Numidiaphyllum is one of the Paleozoic scleractiniamorphs. The genus is characterized by a poorly integrated, uniserial fasciculate form with an epithecate wall and simple morphological traits. Parent corallites are divided into several daughter corallites using one mode of division among several theoretically possible alternatives. Bipartite increase is most common, followed by hexapartite and then tripartite increase. Daughter corallites possess relatively large diameters from the beginning, along with a robust colonial pattern. This parricidal increase caused the morphologies of both parent and daughter corallites to be greatly altered and to show high morphological variability. For ecological and structural reasons, co-occurring daughter corallites generally are equal or subequal in size. Daughter corallites initially show a bilateral symmetry in both outline and septal arrangement during the course of hystero-ontogeny. However, this symmetry results only from structural necessity and is transitory. It is not homologous with the bilaterality of body plans characteristic of anthozoan groups. The morphological simplicity, related parricidal reproduction, and resulting poorly integrated growth form as seen in Numidiaphyllum, all suggest conservative features that could have resulted from phylogenetic antiquity within the scleractiniamorph body plan. Those generalized features are not themselves related to immediate phylogenetic relationships with any simply constructed rugosan group, nor would they have been due to surrounding, stressful ecologic conditions. They may have been phylogenetic-specific.