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Functional significance of regular archaeocyathan central cavity diameter: a biomechanical and paleoecological test

  • Michael Savarese (a1)


Theoretical and experimental biomechanical approaches are used to test the effect regular archaeocyathan central cavity diameter has on the generation of passive flow through the skeleton. These results are then used to predict a correspondence between gross morphology and paleoenvironmental occurrence. Previous work has demonstrated that regular archaeocyathan morphology generates passive flow, via Bernoulli and viscous entrainment effects, through its porous walls for suspension feeding, a phenomenon that occurs in modern sponges. Efficacy of entrainment depends upon the area of the excurrent pore (i.e., central cavity) over which the ambient flow is moving. Consequently, archaeocyaths should have maximized their central cavity diameters.

Five-centimeter-long, conical and cylindrical acrylic pipes with varying end diameters were tested in a flume to document the relative effects of Bernoulli and viscous entrainment. Each pipe was oriented perpendicular to the flow direction in a uniform flow field, and fluorescein dye was injected at the pipe's mid-length for flow visualization. Models with different-sized apertures consistently exhibit dye movement to the larger opening and greater dye entrainment speeds than models with identically sized apertures, thereby suggesting that viscous entrainment effects are significant and operating in concert with Bernoulli effects. To test for similar effects in archaeocyaths, four brass models were constructed with varying central cavity diameters. Both volume flux and excurrent flow speed of the exiting water increased as the central cavity diameter increased. An analysis of the morphologies that occur in nature confirm these results. Regular archaeocyaths most commonly have central cavity diameters close to their outer wall diameter, thereby maximizing the excurrent pore area.

These results have implications for archaeocyathan paleoecology. Environments with low-magnitude currents should support individuals with larger central cavity diameters than higher energy settings. Data on the occurrence of morphotypes within bioherms of varying flow energies from South Australia support this prediction.



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Functional significance of regular archaeocyathan central cavity diameter: a biomechanical and paleoecological test

  • Michael Savarese (a1)


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