The Silurian and Devonian proetid and aulacopleurid trilobites of Japan and their palaeogeographical significance

Abstract

Trilobites referable to the orders Proetida and Aulacopleurida are geographically widespread in the Silurian and Devonian strata of Japan. They are known from the South Kitakami, Hida-Gaien and Kurosegawa terranes. Revision of other Japanese trilobite groups, most notably the Illaenidae, Scutelluidae and Phacopidae, has extended the palaeobiogeographical ranges of several Japanese trilobite taxa, but has not signalled conclusive evidence of a consistent palaeogeographical affinity. In part, this may relate to the temporally and spatially fragmented Palaeozoic record in Japan, and perhaps also to the different ecological ranges of the trilobites. Here, we present a taxonomic revision of all previously described proetid and aulacopleurid trilobites from Japan, along with descriptions of new material, which comprises thirteen species (one new: Interproetus mizobuchii n. sp.) within nine genera, with three species described under open nomenclature. These trilobites show an endemic signal at species level, not just between Japan and other East Asian terranes, but also between individual Japanese terranes. This endemicity may be explicable in terms of facies and ecology, rather than simply being a function of geographical isolation. □ Aulacopleurida, Devonian, Japan, palaeogeography, Proetida, Silurian.