Department of Geology, The Field Museum, Chicago, IL 60605, USA.
Proc Natl Acad Sci U S A. 2011 Jan 4;108(1):232-7. doi: 10.1073/pnas.1011924108. Epub 2010 Dec 20.
Interpreting key ecological parameters, such as diet, of extinct organisms without the benefit of direct observation or explicit fossil evidence poses a formidable challenge for paleobiological studies. To date, dietary categorizations of extinct taxa are largely generated by means of modern analogs; however, for many species the method is subject to considerable ambiguity. Here we present a refined approach for assessing trophic habits in fossil taxa and apply the method to coelurosaurian dinosaurs--a clade for which diet is particularly controversial. Our findings detect 21 morphological features that exhibit statistically significant correlations with extrinsic fossil evidence of coelurosaurian herbivory, such as stomach contents and a gastric mill. These traits represent quantitative, extrinsically founded proxies for identifying herbivorous ecomorphology in fossils and are robust despite uncertainty in phylogenetic relationships among major coelurosaurian subclades. The distribution of these features suggests that herbivory was widespread among coelurosaurians, with six major subclades displaying morphological evidence of the diet, and that contrary to previous thought, hypercarnivory was relatively rare and potentially secondarily derived. Given the potential for repeated, independent evolution of herbivory in Coelurosauria, we also test for repetitive patterns in the appearance of herbivorous traits within sublineages using rank concordance analysis. We find evidence for a common succession of increasing specialization to herbivory in the subclades Ornithomimosauria and Oviraptorosauria, perhaps underlain by intrinsic functional and/or developmental constraints, as well as evidence indicating that the early evolution of a beak in coelurosaurians correlates with an herbivorous diet.
在没有直接观察或明确化石证据的情况下，解释已灭绝生物的关键生态参数，如饮食，这对古生物学研究来说是一个巨大的挑战。迄今为止，灭绝分类群的饮食分类主要是通过现代类似物来进行的；然而，对于许多物种来说，这种方法存在很大的不确定性。在这里，我们提出了一种评估化石分类群营养习惯的改进方法，并将该方法应用于兽脚亚目恐龙——一种饮食特别有争议的恐龙。我们的研究结果发现了 21 个形态特征，这些特征与兽脚亚目恐龙草食性的外在化石证据（如胃内容物和胃磨）具有统计学上的显著相关性。这些特征代表了识别化石中草食性生态形态的定量、外在的代理指标，并且在主要兽脚亚目亚群的系统发育关系存在不确定性的情况下仍然具有稳健性。这些特征的分布表明，草食性在兽脚亚目中非常普遍，六个主要亚群都具有饮食的形态学证据，与之前的观点相反，超肉食性相对较少，而且可能是次要衍生的。考虑到在兽脚亚目中草食性可能会重复、独立进化，我们还使用等级一致性分析来测试亚系内草食性特征出现的重复性模式。我们发现，在兽脚亚目下的鸟脚类和偷蛋龙类中，有证据表明向草食性的专门化有共同的演变趋势，这可能是由内在的功能和/或发育限制所决定的，也有证据表明，在兽脚亚目中喙的早期进化与草食性饮食相关。
