FOULING FILTRATION FANS: HOW CHANGING SEDIMENTOLOGICAL REGIMES CHANGED FAN ORIENTATION IN BOTTOM DWELLING BLASTOIDS
Blastoid abundance and diversity was greatly reduced in the Late Paleozoic crinoid faunas, particularly in North American and Europe. However, they were abundant in Paleo-Tethyan Permo-Carboniferous crinoid communities. Bottom dwelling blastoids from these faunas lived in a greater range of sedimentological settings and were far more abundant and diverse than earlier bottom-dwelling genera. Apparently they were able to tolerate greater clastic sediment input by orienting the oral-aboral axis perpendicular to the bottom. The filtration fans were oriented parallel to the sediment water interface. Morphologic strategies to accomplish the strategy varied. Some taxa sat directly on the seafloor with ambulacra confined to the adoralmost surface. Others expanded the lower part of the theca into radiate, star-shaped extensions in a lunar module strategy. Still others used a rocket strategy with the theca resting on the aboral tips of the radials. Many of these taxa have long deltoids and ambulacra. Brachiole attachment scars are typically missing aborally on the ambulacra indicating that the filtration fan was elevated. Hydrospires often do not extend below the radio-deltoid suture in these taxa. All of these taxa have diminutive stems that may reflect an ontogenetic shift to bottom dwelling in adulthood.