First fossil crabs (Crustacea, Decapoda, Brachyura) from the Kerguelen Islands (Miocene) with exceptionally preserved gills

Abstract. Kerguelen Islands are predominantly volcanic lands, thus fossil references are very uncommon. However, its Miocene fossils are of specific interest for understanding migration routes of some taxa during the Cenozoic, given the intermediary position of Kerguelen with various continents. Despite this fossil rarity, we studied herein hundreds of nodules corresponding to the sole known fossil brachyurans (and unique Decapoda) from Kerguelen both for their systematics and their preservation. Indeed, these crabs display some internal fragile structures that are rarely fossilized, such as the gills' branchial lamellae, preserved in volume. The preservation of these gills and their diagenetic features were documented through traditional imagery (SEM), including morphological comparison to modern gills, and with petrographic and geochemical analyses (EDS, X-ray diffractometry). Some cheilostome bryozoans were observed as probable foulers of the crabs carcasses. The fossil material corresponds to a new ca...