SUPERGIANT TRIASSIC CRUSTACEAN FROM NEVADA: THE OLDEST KNOWN AMPHIPOD

The Upper Triassic (Norian) Luning Formation of Nevada has yielded a deep‑marine, supergiant amphipod from a locality just outside of Berlin-Ichthyosaur State Park. The fossil is associated with giant ichthyosaurs (Shonisaurus) and the deep-water ichnofossil Protopaleodictyon. Pereion and pereiopod morphology of the amphipod fossil suggest affinities with the Acanthogammaridae, a family of giant amphipods largely endemic to Lake Baikal. The large size (17 cm) of the Triassic amphipod indicates that supergiant, deep marine amphipods comparable to modern Alicella gigantea were extant during the Mesozoic. By analogy with Alicella gigantea, the Triassic amphipod was a necrophagous, benthopelagic scavenger that fed on ichthyosaur and other sea floor carcasses. The Nevadan specimen appears to be the oldest known fossil amphipod. This discovery extends the known stratigraphic range of the Amphipoda by at least 170 million years.

Acid maceration of a gastropod‑rich dark limestone from the upper part of the Shaly Limestone Member of the Luning Formation has produced silicified chelae belonging to an undescribed decapod crustacean. A scimitar‑like dactyl, saw teeth on the propus, and a curved tooth at the base of the dactyl (for cracking shells) indicate that this tiny claw had a Swiss Army knife‑like facility for durophagous predation. As such, we hypothesize that this chelate crustacean may have been the very organism that initiated the Mesozoic Marine Revolution (MMR), an important paleoecological development that led to a series of antipredatory measures on the part of the benthic marine biota.