The Oldest Known Stalk-eyed Trilobite, Parablackwelderia Kobayashi, 1942 (damesellinae, Cambrian), and Its Occurrence in Shandong, China

Parablackwelderia is the oldest known stalk-eyed trilobite and thrived during the middle–late Cambrian (Guzhangian Age) in eastern Gondwanaland. The elongated palpebral lobe extends outward and forward from the anterior corner of the cranidium and shows positive allometry, becoming markedly longer and relatively thinner in large specimens. The animal occurred in muddy environments and may have been a predator that burrowed for concealment. Stalked-eyes were independently derived in several trilobite clades, but whenever they appeared were restricted to small numbers of taxa and thus do not appear to have served as a key innovation that promoted extensive diversification of species bearing the structure. The stalk-eyed condition in trilobites has a striking modern analog in the hypercephaly of diopsinid flies, where it is commonly associated with mate recognition and mate selection. We document the first occurrence of Parablackwelderia in Shandong, North China and describe a new species, Parablackwelderia luensis sp. nov.