Description of a new potential fossil hydromedusa Palaequorea rygoli and revision of the fossil medusa Hydrocraspedota mayri from the Plattenkalks of the Franconian Alb, Southern Germany

摘要

Due to their low fossilization potential, Cnidarian medusae have a very sparse fossil record. Many fossils, especially from Ediacaran faunas, have been described as `medusoid' organ-isms so far. However, often a confident assignment to a specific class or a comparison with extant taxa is impossible, as diagnostic morphological features are missing or unclear. Here, we introduce new finds of potential fossil hydromedusae from the Upper Jurassic Solnhofen Archipelago and describe them as Palaequorea rygoli g. nov. sp. nov., for which we suggest a modern analogue like the extant genus Aequorea. This study compares 'bona fide' finds of fossil medusae from the Solnhofen Archi-pelago and elsewhere to the new finds. Following on from the comparison and resulting re-inspection of the holotype, a revised description of Hydrocraspedota mayri shows it to be more comparable to a semaeostome medusa rather than hydromedusa as which it was originally described. Our study high-lights how little Cnidarian medusae have obviously changed since the Jurassic and how important it is to use extant material for comparison in order to elucidate the possible identity and morphology of fossil finds. We hope that this example will stimulate the re-examination of some problematica in the fossil record and may lead to a reassessment of further taxa.