Hopkins Melanie J, Smith Andrew B
Division of Paleontology, American Museum of Natural History, New York, NY 10024; and
Department of Earth Sciences, The Natural History Museum, London SW7 5BD, United Kingdom.
Proc Natl Acad Sci U S A. 2015 Mar 24;112(12):3758-63. doi: 10.1073/pnas.1418153112. Epub 2015 Feb 23.
How ecological and morphological diversity accrues over geological time has been much debated by paleobiologists. Evidence from the fossil record suggests that many clades reach maximal diversity early in their evolutionary history, followed by a decline in evolutionary rates as ecological space fills or due to internal constraints. Here, we apply recently developed methods for estimating rates of morphological evolution during the post-Paleozoic history of a major invertebrate clade, the Echinoidea. Contrary to expectation, rates of evolution were lowest during the initial phase of diversification following the Permo-Triassic mass extinction and increased over time. Furthermore, although several subclades show high initial rates and net decreases in rates of evolution, consistent with "early bursts" of morphological diversification, at more inclusive taxonomic levels, these bursts appear as episodic peaks. Peak rates coincided with major shifts in ecological morphology, primarily associated with innovations in feeding strategies. Despite having similar numbers of species in today's oceans, regular echinoids have accrued far less morphological diversity than irregular echinoids due to lower intrinsic rates of morphological evolution and less morphological innovation, the latter indicative of constrained or bounded evolution. These results indicate that rates of evolution are extremely heterogenous through time and their interpretation depends on the temporal and taxonomic scale of analysis.
在地质时间尺度上，生态和形态多样性是如何积累的，一直是古生物学家们激烈争论的话题。化石记录的证据表明，许多进化枝在其进化历史的早期就达到了最大多样性，随后随着生态空间的填满或由于内部限制，进化速率下降。在这里，我们应用最近开发的方法来估计主要无脊椎动物进化枝——海胆纲在古生代之后的历史时期内的形态进化速率。与预期相反，在二叠纪-三叠纪大灭绝后的多样化初始阶段，进化速率最低，且随时间增加。此外，尽管几个亚进化枝显示出较高的初始速率和进化速率的净下降，这与形态多样化的“早期爆发”一致，但在更广泛的分类水平上，这些爆发表现为间歇性峰值。峰值速率与生态形态的主要转变相吻合，主要与摄食策略的创新有关。尽管在当今海洋中，规则海胆和不规则海胆的物种数量相似，但由于形态进化的内在速率较低和形态创新较少，规则海胆积累的形态多样性远低于不规则海胆，后者表明进化受到限制或约束。这些结果表明，进化速率在时间上极其不均一，其解释取决于分析的时间和分类尺度。
