Data from: Antitropicality and convergent evolution: a case study of Permian neospiriferine brachiopods

Antitropical distribution is a biogeographical pattern characterized by natural occurrences of the same species or members of the same clade in the middle- or middle-to-high-latitudinal habitats of both hemispheres, either on land or in marine environments, without appearing in the intervening tropical environments. For most of the noted examples of Permian antitropical distribution, particularly in marine invertebrates, the causes of disjunctions have been mainly linked to either dispersal or vicariance models. Little attention has been paid to other possible mechanisms. This study investigated the antitropicality of some Permian neospiriferine brachiopods through detailed taxonomic revision, comparison of palaeobiogeographical distribution, and a phylogenetic analysis. Several species, previously assigned to Kaninospirifer, are here reassigned to other genera, especially to Fasciculatia in the northern hemisphere and to Quadrospira in the southern hemisphere during the Permian. Both Kaninospirifer and Fasciculatia appear to have been restricted to north-western Pangea and north-eastern Asia during the Permian, but there is no robust evidence to suggest their presence in the southern hemisphere to which Imperiospira and Quadrospira were confined. In spite of the distributional separation between the two pairs of neospiriferine genera in the Permian palaeobiogeographical regime, they share considerable numbers of morphological characters, such as a large shell, subdued fasciculation, and reduction of ventral adminicula. Notwithstanding these morphological similarities, our phylogenetic reconstruction of the neospiriferines does not support a close relationship between these genera. This therefore must indicate that these similar morphological features were independently acquired, probably with these taxa living in spatially separate but ecologically compatible environmental conditions in the mid-latitudinal area of each hemisphere during the Permian. We regard this as an example of convergent evolution.反热带分布（antitropical distribution）是一类生物地理格局，其典型特征为同一物种或同一支系（clade）的类群，可在陆生或海洋环境下的南北半球中纬度及中高纬度生境中自然分布，却不会出现在二者之间的热带区域内。针对多数已记载的二叠纪（Permian）反热带分布实例，尤其是海洋无脊椎动物（marine invertebrates）类群，其分布间断的成因多被归因于扩散模型（dispersal model）或隔离分化（vicariance）模型，而其他潜在机制则长期未得到足够关注。本研究通过详细的分类学修订（taxonomic revision）、古生物地理分布（palaeobiogeographical distribution）对比以及系统发育分析（phylogenetic analysis），对部分二叠纪新石燕族（neospiriferine）腕足类（brachiopods）的反热带分布特征开展了系统性探究。此前被划归至卡尼石燕属（Kaninospirifer）的多个物种，本次研究将其重新归入其他属类；二叠纪时期，北半球的此类物种多被归入束形石燕属（Fasciculatia），南半球的则多归入四旋石燕属（Quadrospira）。二叠纪期间，卡尼石燕属与束形石燕属的分布范围似乎均局限于泛古陆（Pangea）西北部与东北亚区域，但目前尚无确凿证据表明它们曾出现在南半球——而南半球正是帝国石燕属（Imperiospira）与四旋石燕属的分布区域。尽管这两对新石燕族属在二叠纪古生物地理体系中存在显著的分布分隔，但二者共享诸多形态特征，例如壳体硕大、束状纹饰弱化以及腹茎突（ventral adminicula）的退化。即便存在上述形态相似性，我们针对新石燕族的系统发育重建（phylogenetic reconstruction）结果并不支持这些属类之间存在紧密的亲缘关联。这意味着这些相似的形态特征应为独立演化而来，推测这些类群在二叠纪时期分别栖息于两个半球的中纬度区域，虽空间相互隔离却处于生态兼容的环境条件中。我们将此案例视作趋同演化（convergent evolution）的典型实例。