Iterative evolution has proved a difficult evolutionary phenomenon to study and interpret. Inferences of causality vary from study to study and quantitatively based phylogenetic reconstruction has never been attempted. In an effort to better understand iterative evolution we employed stratocladistics, gap analysis and disparity analysis to study the case of the Monograptidae in the aftermath of the late Silurian Cyrtograptus lundgreni extinction event. Our combination of gap analytical and stratocladistic techniques allowed us to elucidate the evolutionary relationships between the studied taxa. Based on our stratocladistic results we recommend the generic reassignment of five monograptid taxa. The stratocladistic results, in conjunction with morphological disparity analysis suggest the presence of a persistent developmental potential for the emergence of iteratively evolving characters. This persistent potential appears to be limited by extrinsic ecological constraints, which would have relaxed in the aftermath of the C. lundgreni extinction event. Our findings indicate that iterative evolution in the late Silurian Monograptidae is a product of the interaction of both intrinsic and extrinsic constraints on the acquisition of the iteratively evolving character, with the exact causality being dependent on the particular character.

中文翻译：

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更好地理解迭代演化：来自波罗的海盆地的志留纪晚单足纲科（Graptolithina）的例子

迭代进化已证明是难以研究和解释的进化现象。因果关系的推论因研究而异，从未尝试过基于定量的系统发育重建。为了更好地理解迭代进化，我们采用了平地层学，缺口分析和差异分析来研究志留纪Cyrtograptus lundgreni后期的独角兽科的情况。灭绝事件。缺口分析和平流层技术的结合使我们能够阐明所研究分类群之间的进化关系。根据我们的平层研究结果，我们建议对五个单粒类群进行通用分配。平流层化的结果，结合形态差异分析表明，存在不断发展的潜力，不断出现演化的字符。这种持久的潜力似乎受到外部生态约束的限制，而外部生态约束本可以在C. lundgreni的后果之后得到缓解。灭绝事件。我们的发现表明，志留纪单足类动物晚期的迭代演化是内在和外在约束条件对迭代演化特征的获取的相互作用的产物，确切因果关系取决于特定特征。