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When a groove is not a groove: Clarification of the appearance of the dentary groove in tyrannosauroid theropods and the distinction between Nanotyrannus and Tyrannosaurus. Reply to Comment on: 'Distribution of the dentary groove of theropod dinosaurs: implications for theropod phylogeny and the validity of the genus Nanotyrannus Bakker et al., 1988'

机译:当凹槽不是凹槽时:澄清霸王龙兽脚类中齿状凹槽的外观,并区分纳米霸王和霸王龙。对以下问题的评论答复:“兽脚类恐龙齿槽的分布:对兽脚类动物系统发育的影响以及Nanotyranranss Bakker等人的有效性,1988年”

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The occurrence of a lateral groove in the dentary of theropod dinosaurs was argued to be a key diagnostic character for establishing the validity of Nanotyrannus lancensis as a unique taxon separate from Tyrannosaurus rex by Schmerge and Rothschild (2016). The validity of this distinction has been challenged in a comment paper by Brusatte et al. (2016). The main criticisms raised in this comment address the methodology of the original study, the distribution of the dentary groove in theropods, the possibility of ontogenetic variability in the occurrence of the dentary groove, and the application of phylogenetic analysis to studying character distributions. In this reply, we clarify the definition of the theropod dentary groove, elucidate the difference between a true dentary groove and the appearance of a false "pseudo-groove", justify our original methodology with a discussion of the errors involved in identifying grooves by Brusatte et al. (in press), and support our original findings with descriptions of additional specimens. Investigation of additional specimens of Nanotyrannus, as well as critical examination of Tyrannosaurus specimens presented by Brusatte et al. (2016), reaffirm the result of our original study that Nanotyrannus can be differentiated from Tyrannosaurus based on the depth of its dentary groove, independent of ontogenetic stage. Despite any possible ontogenetic variation in the appearance of the dentary groove that can be interpreted, all specimens of Nanotyrannus possess distinct grooves whereas Tyrannosaurus lacks a groove. The most parsimonious explanation for the different appearance of these grooves is that Nanotyrannus does not represent a juvenile Tyrannosaurus. (C) 2016 Elsevier Ltd. All rights reserved.
机译:Schmerge和Rothschild(2016)认为在兽脚亚目恐龙的齿状齿中出现侧向沟纹是确立纳米霸王龙作为与霸王龙分离的独特分类的有效性的关键诊断特征。 Brusatte等人在评论文件中对这种区别的有效性提出了质疑。 (2016)。该评论提出的主要批评涉及原始研究的方法,兽脚类中齿槽的分布,齿槽发生中个体发育变异的可能性以及系统发育分析在研究字符分布中的应用。在此答复中,我们阐明了兽脚类恐龙齿槽的定义,阐明了真正的齿槽与假“假槽”的出现之间的区别,并通过讨论布鲁萨特在识别沟槽方面的错误来证明我们的原始方法是正确的等。 (印刷中),并通过其他标本的描述来支持我们的原始发现。研究其他霸王龙标本,以及对Brusatte等人提出的霸王龙标本进行严格检查。 (2016),重申了我们最初研究的结果,即可以根据齿槽的深度将霸王龙与霸王龙区分开,而与个体发育阶段无关。尽管可以解释的牙槽沟的外观可能存在个体差异,但所有的纳米暴龙标本都具有明显的沟纹,而霸王龙则没有沟纹。对于这些凹槽的不同外观的最简约的解释是,纳米霸王龙并不代表幼年的霸王龙。 (C)2016 Elsevier Ltd.保留所有权利。

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