Global Review of Permian Tyloplecta Muir-Wood and Cooper, 1960 (Brachiopoda): Morphology, Palaeobiogeographical and Palaeogeographical Implications

Abstract

A global review of the stratigraphical and geographical distribution of Tyloplecta reveals that the genus ranges in age from Kungurian to Changhsingian (Middle to Late Permian). Tyloplecta first evolved in South China in the Kungurian (late Early Permian). The genus went through its first diversification in the Guadalupian, suffered a major extinction at the end of the Guadalupian, and re-diversified in the Wuchiapingian. T. yangtzeensis persisted into the Changhsingian as the only survivor of the genus involved in the end-Permian mass extinction. Palaeogeographically, South China is not only the centre of origin for the genus but also an area of diversification and evolution. In addition to South China, Tyloplecta has also been recorded from the Far East Russia, Japan, central Thailand, Laos, Cambodia, Qiangtang Terrane of Tibet, Salt Range, Iran, Armenia, Hungary, Yugoslavia, and Slovenia. This geographic spread suggests that Tyloplecta was primarily restricted to the Palaeotethys and is indicative of warm-water palaeoequatorial conditions. Its presence in some of the northeast Asian terranes (e.g., parts of Japan and Far East Russia) and in the Salt Range (Pakistan) and central and north Iran (part of the Cimmerian microcontinents) demonstrate that the genus invaded the middle palaeolatitudinal regions in both hemispheres during the late Middle Permian in response to increased shallow marine biotic communications between Cathaysia in the eastern Palaeotethys and southern Angaraland, and between Cathaysia and Peri-Gondwanaland. The invasion of Tyloplecta (and some other taxa) into the southern shore waters of Angaraland may be explained by assuming ocean surface current connections and close palaeogeographical proximities between the South China, Sino-Korea and Bureya blocks. In comparison, the invasion of Tyloplecta into the Peri-Gondwanaland region is more likely a result of reduced palaeogeographical distance between South China and Peri-Gondwanaland and the appearance of the Cimmerian microcontinents as migratory stepping stones.