Bird-like characteristics of troodontid theropod eggshell
Bird-like characteristics of troodontid theropod eggshell
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DOI：
10.1006/cres.2002.1010
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发表时间：
2002-06
影响因子：
2.1
通讯作者：
D. Zelenitsky;S. Modesto;P. Currie
中科院分区：
文献类型：
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作者：
D. Zelenitsky;S. Modesto;P. Currie
对保存完好的兽脚亚目恐龙formosus的蛋壳化石（卵种Prismatoolithus levis）的描述，揭示了化石和现代鸟类蛋壳的共同特征。齿形动物蛋壳的类似鸟类的特征包括：与附着在乳突基部的等球粒相关的纤维，形成球粒并渐变成块状楔状乳突的精细辐射晶体，以及外层呈现鳞状超微结构的棱柱。蛋壳内的两层（乳状层和鳞状层）要么是兽脚亚目畸形，要么是兽脚亚目内部形成的；冠群鸟类的外蛋壳层相对于其他兽脚亚目动物的蛋壳是不对称的。尽管在鸟类的姐妹分类群上存在分歧，但最近的兽脚亚目系统发育强有力地表明，在Troodontidae和Neognathae中，棱柱状超微结构是独立进化的。我们在原认为缺乏鳞状超微结构的齿形兽蛋壳中发现了鳞状超微结构，揭示了先前将这种蛋壳分配到恐龙-棱柱形形态型以及当前蛋壳准分类学中蛋壳形态型概念的问题。我们的结论是，恐龙-棱柱形形态应该被抛弃。
Description of well-preserved fossil eggshell (oospecies Prismatoolithus levis), recently assigned to the theropod dinosaur Troodon formosus, reveals traits that are shared with the eggshell of both fossil and Recent avians. Bird-like characteristics of troodontid eggshell include: fibres associated with eisospherites that are attached to the bases of the mammillae, fine radiating crystals that form the spherulites and grade into blocky wedges of the mammillae, and prisms in the outer layer that exhibit squamatic ultrastructure. The presence of two layers (mammillary and squamatic) within the eggshell is either a theropod apomorphy or it arose within Theropoda; the external eggshell layer of crown-group avians is apomorphic with respect to other theropod eggshell. Despite disagreement on the putative sister taxon of birds, recent theropod phylogenies suggest strongly that prismatic ultrastructure evolved independently in Troodontidae and Neognathae. Our identification of squamatic ultrastructure in troodontid eggshell, which was previously thought to lack this structure, reveals problems with the previous assignment of this eggshell to the dinosauroid-prismatic morphotype and with the concept of eggshell morphotype in the current eggshell parataxonomy. We conclude that the dinosauroid-prismatic morphotype should be abandoned.