A triassic giant amphipod from Nevada, USA

Abstract

A giant fossil amphipod Rosagammarus minichiellus n. gen., n. sp. occurs in a Triassic limestone (Luning Formation, west-central Nevada) in association with ichthyosaurs (Shonisaurus sp.) and the deep-water trace fossil Protopaleodictyon ichnosp. Fossil pereion and pereiopod morphology suggest affinities with Acanthogammaridae, a freshwater amphipod family largely endemic to Lake Baikal. The large size (17 cm) of the Triassic amphipod shows that supergiant, deep marine amphipods comparable to modern Alicella gigantea Chevreux, 1899 were extant during the early Mesozoic. By analogy with A. gigantea, R. minichiellus was likely a necrophagous, benthopelagic scavenger that fed on ichthyosaur and other sea floor carcasses. Rosagammarus minichiellus appears to be the oldest known fossil amphipod, extending the known geological range of Amphipoda by at least 170 million years. © The Crustacean Society, 2013.