Article: Late Ordovician trilobites from southern Thailand

A rich and well-preserved trilobite fauna is described from the upper Ordovician (Caradoc) Pa Kae Formation, Satun Province, southern Thailand. This is the first diverse trilobite fauna of this age to be described from the Shan Thai (Sibumasu) terrane. The fauna represents an outer shelf assemblage of 39 species, dominated by Ovalocephalus, nileids and remopleuridids. It is identical even at the species level to faunas described from the Pagoda Limestone of southern China, indicating that the Shan Thai terrane cannot have been far removed geographically from this part of China in the late Ordovician. The distribution of the Ovalocephalus fauna proves that there are also wider faunal links with western Gondwana and Scandinavia. Most of the species have been previously named from China, but new information is presented for several of them. Examination of the agnostid Arthrorhachis latelimbata proves that cell polygons are a much finer-scale structure than reticulate sculpture. The telephinid Telephina convexa has holochroal eyes constructed of perfectly square lenses: the possibility that these represent reflection superposition eyes is considered. Two new species are proposed: Sculptaspis pulcherrima and Ovalocephalus plewesae.