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）是一种生物地理格局，其特征为同一物种或同一演化支（clade）的类群，可在陆地或海洋环境中同时出现于两个半球的中纬度或中高纬度生境，而在过渡的热带区域无分布记录。对于多数已报道的二叠纪反热带分布实例（尤其是海洋无脊椎动物类群），其分布间断的成因主要被归因于扩散模型或隔离分化模型，其他潜在机制则鲜有受到关注。本研究通过细致的分类学修订、古生物地理分布对比以及系统发育分析，对若干二叠纪新石燕类（neospiriferine）腕足动物（brachiopods）的反热带分布特征开展了研究。此前被归入卡尼石燕属（Kaninospirifer）的多个物种，本次研究将其重新划归至其他属，其中二叠纪北半球类群多归入簇石燕属（Fasciculatia），南半球类群则多归入四旋石燕属（Quadrospira）。二叠纪期间，卡尼石燕属与簇石燕属似乎仅分布于泛大陆（Pangea）西北部与东北亚区域，但尚无可靠证据表明它们存在于南半球——而南半球为帝王石燕属（Imperiospira）与四旋石燕属的分布局限区域。尽管二叠纪古生物地理格局中，这两对新石燕类属群存在分布分隔，但二者共享大量形态特征，例如壳体硕大、簇状纹饰弱化以及腹壳支撑结构（ventral adminicula）的退化。尽管存在这些形态相似性，我们对新石燕类的系统发育重建结果并不支持这些属群间存在紧密的亲缘关系。这表明这些相似的形态特征应是独立演化获得的，可能源于这些类群在二叠纪期间，各自半球的中纬度区域中虽空间隔离但生态环境兼容的生存条件。我们将其视为趋同演化（convergent evolution）的一个实例。