Article: Tanchintongia gen. nov., a bizarre Permian myalinid bivalve from West Malaysia and Japan

Broken pieces of a huge thick-shelled myalinid forming a calcirudite in the Kinta Valley, West Malaysia, show that the live shells rested on spectacular flanges formed by acute bends in the lateral flanks of the valves. Consequently the shells had a large permanent posterior gape, and must therefore have lived below low-tide level. The flanges may have acted like snowshoes to support the animals on the surface of a fine carbonate substrate, or they may have acted as outriggers to prevent overturning. Prominent grooves, formed by the ontogenetic shift in the position of the byssal gape, show that the shells were byssally attached throughout life. Associated ammonoids and fusulines provide an early Permian age for the Malaysian shells; similar fragments occur with Permian fusulines in Japan. Tanchintongia was at least as large and as thick-shelled as its cool temperate analogue Eurydesma, indicating that these features were not simply temperature controlled in Permian bivalves.