Cranial functional morphology of the pseudosuchian Effigia and implications for its ecological role in the Triassic
Cranial functional morphology of the pseudosuchian Effigia and implications for its ecological role in the Triassic
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DOI：
10.1002/ar.24827
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发表时间：
2021-11
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影响因子：
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通讯作者：
J. Bestwick;Andrew S. Jones;S. Nesbitt;S. Lautenschlager;E. Rayfield;A. Cuff;David J. Button;P. Barrett;Laura B. Porro;R. Butler
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作者：
J. Bestwick;Andrew S. Jones;S. Nesbitt;S. Lautenschlager;E. Rayfield;A. Cuff;David J. Button;P. Barrett;Laura B. Porro;R. Butler
拟鳄类是一种与鳄鱼目关系比与鸟类关系更密切的祖龙类爬行动物，在三叠纪期间表现出高度的形态多样性，有许多三叠纪拟鳄类和三叠纪后恐龙之间形态趋同的例子。一个例子是舒沃龙科 Effigia okeeffeae，它表现出一种“类似鸵鸟”的结构，由细长的骨骼组成，下颌无牙，眼眶很大，类似于拟鸟龙和现存的古颌类恐龙。这种鲍普兰被认为是食草动物的适应，但这一假设假设形态趋同会带来功能趋同，并且几乎没有接受过明确的测试。在这里，我们恢复了 Effigia 的头骨形态，进行了肌肉学重建，并应用有限元分析来定量研究头骨功能。我们还对拟鸟科恐龙 Ornithomimus edmontonicus、现存古颌驼鸟和现存拟鳄类密西西比鳄的头盖骨进行了有限元分析，以评估与表现出“鸵鸟样”鲍普兰及其现存近亲的分类单元的功能趋同程度。我们发现，Effigia 拥有一系列机械强弱特征，包括薄弱的下颌骨，可能限制了颌前部的进食。我们发现与似鸟龙和鸵鸟的功能趋同性有限，并且与现存拟鳄类的系统发育限制的证据也有限。我们推断，Effigia 是一种专业的草食动物，可能以较软的植物材料为食，这是研究类群中独特的生态位，也可能是同时代三叠纪草食动物中的一个。这项研究增加了拟鳄类已知的功能多样性，并强调不相关类群之间表面形态的相似性并不总是意味着功能和生态的趋同。
Pseudosuchians, archosaurian reptiles more closely related to crocodylians than to birds, exhibited high morphological diversity during the Triassic with numerous examples of morphological convergence described between Triassic pseudosuchians and post‐Triassic dinosaurs. One example is the shuvosaurid Effigia okeeffeae which exhibits an “ostrich‐like” bauplan comprising a gracile skeleton with edentulous jaws and large orbits, similar to ornithomimid dinosaurs and extant palaeognaths. This bauplan is regarded as an adaptation for herbivory, but this hypothesis assumes morphological convergence confers functional convergence, and has received little explicit testing. Here, we restore the skull morphology of Effigia, perform myological reconstructions, and apply finite element analysis to quantitatively investigate skull function. We also perform finite element analysis on the crania of the ornithomimid dinosaur Ornithomimus edmontonicus, the extant palaeognath Struthio camelus and the extant pseudosuchian Alligator mississippiensis to assess the degree of functional convergence with a taxon that exhibit “ostrich‐like” bauplans and its closest extant relatives. We find that Effigia possesses a mosaic of mechanically strong and weak features, including a weak mandible that likely restricted feeding to the anterior portion of the jaws. We find limited functional convergence with Ornithomimus and Struthio and limited evidence of phylogenetic constraints with extant pseudosuchians. We infer that Effigia was a specialist herbivore that likely fed on softer plant material, a niche unique among the study taxa and potentially among contemporaneous Triassic herbivores. This study increases the known functional diversity of pseudosuchians and highlights that superficial morphological similarity between unrelated taxa does not always imply functional and ecological convergence.