200 Paleontology VII - Consequences of Extinction and Radiation

Tuesday, 2 November 2010
1:30 PM - 5:30 PM
Room 605

RADIATION AND “LEGACY ADAPTATIONS” OF MISSISSIPPIAN CAMERATE CRINOIDS FOLLOWING THE HANGENBERG EXTINCTION OF PREDATORY FISHES

Paper number: 200-7
Program: Technical Sessions
Time: 3:00 PM – 3:15 PM

Authors

Abstract

Global cooling at the end-Famennian Hangenberg Extinction Event led to a post-extinction trough in gnathostome diversity (Sallan and Coates, 2010). Placoderms and sarcopterygians were decimated and replaced by chondrichthyans and actinopterygians which radiated into a variety of new forms by the Visean. The intervening Tournaisian had reduced gnathostome diversity. Crinoid diversity was halved from the Early to Late Devonian, but reached maximum standing diversity for the entire Paleozoic by the late Tournaisian, then declined afterwards. Reduction in predation pressure by gnathostomes during the Tournaisian probably contributed to crinoid peak diversity. Most crinoid clades radiated during the Tournaisian, but the camerates with boxy calyces comprised of numerous, commonly spinose plates were most diverse and abundant, re-establishing their Early Devonian dominance. After the Tournaisian, camerates declined in diversity through the remainder of the Mississippian and Late Paleozoic, whereas the next largest clade, the pinnulate advanced cladids maintained or increased their diversity during the same interval.

Kammer and Ausich (2006) proposed that the Tournaisian crinoid diversity spike and extensive encrinital limestones resulted from widespread carbonate ramps after coral reefs were decimated by the end-Frasnian Kellwasser Extinction Event. We hypothesize that crinoid peak diversity and widespread encrinital limestones of the Tournaisian resulted from the combined effects of separate coral reef and gnathostome extinctions during the Late Devonian. Camerates radiated in the Tournaisian after predatory release from their former predators. Their boxy, spinose calyces, adapted for the slicing and nipping Devonian predators, are an example of “legacy adaptations” that were maladaptive for the new crushing dentition of sharks, holocephalans, and ray-finned fishes that radiated in the Mississippian. Although the camerates were relatively unscathed by the Hangenberg Extinction Event, the loss of their co-evolved predators allowed the evolution of newer, more effective, predators that ended their dominance of crinoid faunas.