A new polychelidan lobster from the Lower Jurassic of southeastern Switzerland
Résumé
Polychelidan lobsters are a group of decapod crustaceans which, in terms of both numbers of species and morphology, were more diverse during the Triassic and Jurassic than their modern representatives (Polychelidae). Here a new genus and species from the Lower Jurassic of Switzerland, Angusteryon oberlii, is described. The new taxon is characterised by a particularly narrow cephalothoracic shield, which is an unusual trait in comparison to all other polychelidan lobsters, both fossil and extant. It is tentatively assigned to the Coleiidae here. A. oberlii nov. gen., nov. sp. was recovered from hemipelagic sedimentary rocks, suggesting that it inhabited a deep-water setting. Although there is a possibility that the present specimens could be parautochthonous, the small size of the ocular incisions may indicate that A. oberlii nov. gen., nov. sp. had either reduced vision or was blind, which could be explained by its having inhabited a deep-water habitat. If our views on this mode of life and taxonomic assignment are correct, this would suggest convergent degeneration of vision between the new taxon and the Polychelidae. Furthermore, features of the newly collected specimen augment the apparent morphological diversity displayed by polychelidan lobsters early in their history, as well as document a more substantial decrease of such since the Triassic and Jurassic than previously recorded.