Functional morphology of the anastomosing frondose growth form reported in Heterotrypa frondosa (d'Orbigny) (Bryozoa: freposlomata) from the Cincinnatian (Late Ordovician) of Ohio

It has been rare for paleontologists to reconstruct bryozoan zoaria from the fragmented remains that generally represent these structures in Paleozoic rocks. Without reconstructed specimens, however, there can be little understanding of the functions of the colony, its range of phenotypic variation, or the range of ecological conditions for which a species was adapted. A limestone-to-shale interrai in the lower Bellevue Formations has yielded large portions of the skeleton of Hcterotrypo frondosa (d’Orbigny) that was reassembled from more than 60 pieces. External currents drove water through the colony whereas ciliary beat of lophophores created food-capturing opportunities in this passive flow situation. Study in a re-circulating flume using a thermistor-based flow meter and dye, allowed analysis of water movements. First, water velocity was slowed in the chambers; secondly, turbulence was created within the chambers. With slowed velocity, zooids could continue to feed at higher ambient current velocities. Turbulence in chambers was beneficial, allowing the interior polypides of the colony to feed with minimal re-filtering; the turbulence immediately mixed fresh and food-depleted water, retaining food-rich waters in the water mix longer before flushing, as a nonchambered system would have done. Chambers and coalesced blades created a robust, internally-buttressed zoarium that was able to withstand normal, shallow-water, wave conditions as well as occasional storm surges.