Morphological Evolution and Diversification in the Earliest Herbivorous Tetrapod

石炭纪四足类(陆地脊椎动物)食草动物的起源是陆地脊椎动物生态系统建立过程中的一个重要事件。到古生代末，食草动物至少独立进化了8次，这些趋同的进化起源为研究适应性辐射期间的形态进化、会聚和分割模式提供了一个理想的案例研究。适应性辐射是指当谱系利用新的适应区时，与生态相关的性状之间的形态变化。可以通过以下方式创建新的适应性区域：允许该分支访问以前未使用的资源的“关键创新”；新资源的出现；或者该适应性区域的先前占有者的灭绝。古生代食草性四足动物为研究这三种模式提供了机会。化石记录中记载了许多形态上的创新，以允许对植物物质的开发。在石炭纪和二叠纪，植物经历了几次多样化和周转事件，可能提供了新的可开发材料。最后，昆古尔期末期的一次被称为奥尔森灭绝的灭绝事件为研究大规模灭绝后新的食草动物谱系的辐射提供了一个机会。在这个项目中，我的目标是回答三个问题：古生代食草动物的头骨进化模式与适应性辐射模型的预测是否一致？在适应性辐射期间，食草动物独立的、同时代的起源是否表现出与生态位划分一致的生态形态分化？古生代食草动物的形态多样性和物种丰富度的格局是否与植物的多样性格局有关？这些问题将用一系列量化进化的方法来研究。离散的字符数据将使用最近提出的统计方法进行检查，以确定字符变化率中形态多样性变化的趋势。古生代食草动物头骨将被标记以量化头骨形状，这些形状数据将被用于评估古生代食草动物不同支系之间的形态重叠。草食动物和植物的物种丰富度估计，经过不完全抽样修正后，将进行比较，以确定两者之间的相互作用。这项研究的目的是极大地提高我们对陆地生态系统建立的关键时期的理解，以及对适应性辐射的机制的理解。

The origin of herbivory in tetrapods (land vertebrates) during the Carboniferous was a crucial event in the establishment of terrestrial vertebrate ecosystems. Herbivory had evolved independently at least eight times by the end of the Paleozoic, and these convergent evolutionary origins provide an ideal case study for examining patterns of morphological evolution, convergence and partitioning during adaptive radiations. An adaptive radiation is the morphological diversification among ecologically-relevant traits that occurs when lineages exploit a new adaptive zone. The new adaptive zone may be created by: a “key innovation” allowing the clade to access previously unused resources; the appearance of a new resource; or the extinction of the previous occupants of the adaptive zone. Paleozoic herbivorous tetrapods provide an opportunity to study all three modes. Numerous morphological innovations are documented in the fossil record to allow exploitation of plant matter. Plants underwent several diversification and turnover events during the Carboniferous and Permian, potentially providing new material to be exploited. Finally, an extinction event dubbed Olson’s extinction at the end of the Kungurian stage provides an opportunity to study the radiation of new herbivorous lineages following a mass extinction. In this project, I aim to answer three questions: Are patterns of craniodental evolution in Paleozoic herbivores consistent with the predictions of adaptive radiation models? Do the independent, contemporaneous origins of herbivory show ecomorphological differentiation consistent with niche partitioning during adaptive radiations? Are patterns of morphological diversity and species richness in Paleozoic herbivores related to the diversification patterns of plants? These questions will be examined using a wide range of methods for quantifying evolution. Discrete character data will be examined using recently-proposed statistical methods to identify trends in morphological diversity variation in rates of character change. Paleozoic herbivore skulls will be landmarked to quantify skull shape, and this shape data will be used to assess morphological overlap between the different clades of Paleozoic herbivores. Species-richness estimates both of herbivores and plants, corrected for incomplete sampling, will be compared to identify interactions between the two. This research aims to greatly improve our understanding, not only of the critical period in the establishment of terrestrial ecosystems, but also the mechanisms underlying adaptive radiations.