The last chapter of the evolutionary history of the Permian (Artinskian–Wuchiapingian) endemic bivalves of the Passa Dois Group, Brazil, is depicted. They evolved in a vast, isolated epeiric sea under progressive continentalization. Previously, bivalves that thrived during times of marked non-marine (limnic) conditions have been poorly investigated. Hence, a systematic survey of the bivalves between the Leinzia similis assemblage (Serrinha Member) and the Palaeomutela platinensis assemblage (Morro Pelado Member), Rio do Rasto Formation, is presented. Over two hundred specimens were examined, and three bivalve assemblages were identified: (a) the Terraia decarinata assemblage in the uppermost part of the Serrinha Member, including Relogiincola delicata gen. et sp. nov., Palaeomutela australis sp. nov., and Palaeomutela platinensis (Reed, 1935); (b) the Terraia cf. decarinata assemblage in the transition between the Serrinha and Morro Pelado members, including T. decarinata, and P. platinensis, and (c) the Palaeomutela australis assemblage in the lowermost part of the Morro Pelado Member, also including R. delicata and P. platinensis. The investigated bivalves were recorded above the last occurrences of Terraia altissima (Holdhaus, 1918) and Cowperesia emerita Mendes, 1952 in the Serrinha Member. In the Gai-As Formation, Huab Basin, Namibia, these species are found in well-constrained Wordian–Capitanian strata, suggesting a Capitanian–Wuchiapingian age for the studied assemblages. The Permian cosmopolitan freshwater genus Palaeomutela occurs in all three assemblages and is also found in the lower Beaufort Group (South and Central Africa). Therefore, our record may represent the maximum paleobiogeographic expansion of Palaeomutela in Western Gondwana.

中文翻译：

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软体动物演化的三千万年的最后一章：巴西巴拉那盆地的里约杜拉斯托组的二叠纪非海洋双壳类动物

描绘了巴西Passa Dois集团的二叠纪（Artinskian–Wuchiapingian）地方性双壳类动物进化史的最后一章。它们在逐步大陆化的背景下，在辽阔的孤立海域中演化。以前，对双壳类动物在明显的非海洋（褐藻类）状况期间蓬勃发展的研究很少。因此，提出了对Leinzia similis组合（Serrinha成员）和Palaeomutela platinensis组合（Morro Pelado成员）Rio do Rasto组之间的双壳类的系统调查。检查了200多个标本，并确定了三个双壳类动物的组合：（a）Serrinha成员最上部的Terracar decarinata组合，包括Relogiincola delicata gen。等。十一月，Palaeomutela australis sp。nov。，和Palaeomutela platinensis（里德，1935年）；（b）Terraia cf. decarinata装配在塞里尼亚和摩洛佩拉多部件之间的过渡，其中包括T. decarinata，和P. platinensis，和（c）的Palaeomutela芦苇装配在莫罗佩拉多会员的最下部分，另外还包括R. delicata和P. platinensis。被调查的双壳类动物被记录在最后一次出现的Terraia altissima（Holdhaus，1918）和Emperita Cowperesia之上Mendes，1952年担任Serrinha成员。在纳米比亚Huab盆地的Gai-As地层中，这些物种存在于严格约束的Wordian-Capitanian地层中，表明所研究的组合具有Capitanian-Wuchiapingian年龄。二叠纪世界性淡水属Palaeomutela出现在所有三个组合中，并且也出现在Beaufort组的下层（南部和中部非洲）。因此，我们的记录可以代表的最大古生物地理扩张Palaeomutela西方冈瓦纳古陆。