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Functional analysis of archaeocyathan skeletal morphology and its paleobiological implications

  • Michael Savarese (a1)


A biomechanical study of archaeocyathan (phylum Archaeocyatha) skeletal construction was undertaken in order to compare its function with that of poriferans. Flume experiments were conducted on three cylindrical, brass models of regular archaeocyathans. Two of these, the porous-septate and aporous-septate models (i.e., possessing septa either with or without pores), represent an ontogenetic series; regular archaeocyathans (class Regulares) typically exhibit a reduction in septal porosity as they grow and many have aporous septa as adults. The third model is aseptate and represents a morphology that is not found in the fossil record. All models exhibit passive entrainment of flow during flume testing, a phenomenon on which modern sponges depend for suspension feeding. Flow direction through the models is consistent with predictions of the spongiomorph-affinity hypothesis. The three models behave quite differently, however. The aseptate model is least effective at passive entrainment. Although some fluid exits the top of the central cavity (or osculum), a great deal of fluid is entrained out the top of the intervallum and also leaks out the outer wall. Flow induction from the oscula of the septate models is augmented when compared to the aseptate model. The porous-septate model exhibits slight leakage from the outer wall, and a dye-rich plume exits the top of the intervallum. Alternatively, the aporous-septate model exhibits no outer-wall leakage and no entrainment from the intervallum. These differences in flow pattern between the porous- and aporous-septate models suggest a hitherto unknown function for septa. Imperforate septa prohibit the migration of fluid through the intervallum to the low-pressure, downstream side where leakage occurs. The ontogenetic shift in septal porosity, common to many archaeocyathan species, may be a mechanism by which outer-wall leakage is avoided later in life. Archaeocyathans would have encountered progressively higher ambient current velocities as their height increased through growth. Outer-wall leakage is not a problem at low velocities or small sizes, but leakage becomes serious at higher velocities when tall, adult morphologies are attained.



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Functional analysis of archaeocyathan skeletal morphology and its paleobiological implications

  • Michael Savarese (a1)


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