LATE CAMBRIAN AND EARLY ORDOVICIAN TRILOBITES FROM THE SOUTHERN SHAN STATE, MYANMAR

The Shan State of Myanmar, located in the eastern plateau of the country, is part of a continental fragment known as the Sibumasu Terrane, an originally peri-Gondwanan terrane which includes parts of Thailand, Malaysia, and western Yunnan. Cambrian trilobites from the Shan State were first reported in the early 1970s, but no formal descriptions were published until 2021, when material from 3 species belonging to 2 genera were described. Herein we describe a wider variety of trilobites from the Molohein Group’s Myet-Ye Formation (Furongian-Tremadocian) that were collected during two field expeditions in 2016 and 2020 to the southern part of the Shan State.

Fourteen different trilobite taxa comprising 11 genera and six families have been identified from the Shan State material, including (1) two species of Prosaukia previously found in Thailand, (2) an abundance of Eosaukia buravasi, which is endemic to and widespread throughout Sibumasu and exhibits significant intraspecific variation, and (3) two species of Asioptychaspis, a genus commonly found in older strata, but very abundant in the Furongian Shan State material. Other genera include Tsinania, Pseudokoldinioidia, Pagodia, Lichengia, and Pacootasaukia. Current results support an association between the Shan State fauna and those from Ko Tarutao (southern Thailand) and western Australia, as well as potential associations with fauna from the North and South China blocks and the Taebaek Group of South Korea. Despite the many commonalities between the Shan State trilobite fauna and those of western Australia and Ko Tarutao, some genera common to these areas have yet to be recovered in the Shan State, such as Quadraticephalus.

As tuff beds are frequently intercalated among the fossils bearing beds in both the Shan State and on Ko Tarutao, describing Cambrian trilobites from the southern Shan State will help integrate the geochronology of the latest Cambrian, refine paleogeographic reconstructions of the Gondwanan margin at the time, and understand faunal turnover in Gondwana across the Cambrian–Ordovician boundary.