I've been fascinated with the Eugeneodontids (the buzz-saw chondrichthyans) and how they managed to practically become the apex predators of most oceanic environments from the Carboniferous to the Permian with famous members like Edestus and Helicoprion. Two genus of this extraordinary group even survived the Permian-Triassic Extinction 252 Million Years ago - Fadenia and Caseodus!
http://www.fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=34456
http://www.fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=34451
But by the Olenekian stage of the Triassic, the group disappeared. I can understand why the more specialized members of the group like Helicoprion went extinct (ecological specialists and top predators don't do well in events like the Permian-Traissic Extinction event), but what caused the extinction of Fadenia and Caseodus? What occurred in the Triassic that ended the reign of the Eugeneodontids?