PDF(Pubmed)
Abstract：
Non-avialan theropod dinosaurs had diverse ecologies and varied skull morphologies. Previous studies of theropod cranial morphology mostly focused on higher-level taxa or characteristics associated with herbivory. To better understand morphological disparity and function within carnivorous theropod families, here we focus on the Dromaeosauridae, \'raptors\' traditionally seen as agile carnivorous hunters.We applied 2D geometric morphometrics to quantify skull shape, performed mechanical advantage analysis to assess the efficiency of bite force transfer, and performed finite element analysis to examine strain distribution in the skull during biting. We find that dromaeosaurid skull morphology was less disparate than most non-avialan theropod groups. Their skulls show a continuum of form between those that are tall and short and those that are flat and long. We hypothesise that this narrower morphological disparity indicates developmental constraint on skull shape, as observed in some mammalian families. Mechanical advantage indicates that Dromaeosaurus albertensis and Deinonychus antirrhopus were adapted for relatively high bite forces, while Halszkaraptor escuilliei was adapted for high bite speed, and other dromaeosaurids for intermediate bite forces and speeds. Finite element analysis indicates regions of high strain are consistent within dromaeosaurid families but differ between them. Average strain levels do not follow any phylogenetic pattern, possibly due to ecological convergence between distantly-related taxa.Combining our new morphofunctional data with a re-evaluation of previous evidence, we find piscivorous reconstructions of Halszkaraptor escuilliei to be unlikely, and instead suggest an invertivorous diet and possible adaptations for feeding in murky water or other low-visibility conditions. We support Deinonychus antirrhopus as being adapted for taking large vertebrate prey, but we find that its skull is relatively less resistant to bite forces than other dromaeosaurids. Given the recovery of high bite force resistance for Velociraptor mongoliensis, which is believed to have regularly engaged in scavenging behaviour, we suggest that higher bite force resistance in a dromaeosaurid taxon may reflect a greater reliance on scavenging rather than fresh kills.Comparisons to the troodontid Gobivenator mongoliensis suggest that a gracile rostrum like that of Velociraptor mongoliensis is ancestral to their closest common ancestor (Deinonychosauria) and the robust rostra of Dromaeosaurus albertensis and Deinonychus antirrhopus are a derived condition. Gobivenator mongoliensis also displays a higher jaw mechanical advantage and lower resistance to bite force than the examined dromaeosaurids, but given the hypothesised ecological divergence of troodontids from dromaeosaurids it is unclear which group, if either, represents the ancestral condition. Future work extending sampling to troodontids would therefore be invaluable and provide much needed context to the origin of skull form and function in early birds. This study illustrates how skull shape and functional metrics can discern non-avialan theropod ecology at lower taxonomic levels and identify variants of carnivorous feeding.
摘要：
非鸟兽脚类恐龙具有不同的生态和不同的头骨形态。以前对兽脚类动物颅骨形态的研究主要集中在高级分类群或与食草动物相关的特征上。为了更好地了解食肉兽脚类家庭的形态差异和功能，在这里，我们专注于Dromaeosauridae，“猛禽”传统上被视为敏捷的食肉猎人。我们应用2D几何形态计量学来量化头骨形状，进行了机械优势分析，以评估咬合力传递的效率，并进行了有限元分析，以检查咬伤过程中颅骨的应变分布。我们发现，屈毛龙的头骨形态比大多数非鸟兽脚类的差异小。他们的头骨在那些又高又短的头骨和那些又平又长的头骨之间显示出连续的形状。我们假设这种较窄的形态差异表明颅骨形状的发育制约，正如在一些哺乳动物家族中观察到的那样。机械优势表明，扬龙龙和Deinoyorchusantirrhopus适应了相对较高的咬合力，而Halszkaraptorescuilliei适应了高的咬合速度，和其他用于中间咬力和速度的直角龙。有限元分析表明，高应变区域在树龙科内是一致的，但它们之间存在差异。平均菌株水平不遵循任何系统发育模式，可能是由于远缘类群之间的生态趋同。结合我们新的形态功能数据和对先前证据的重新评估，我们发现Halszkaraptorescuilliei的食肉重建不太可能，相反，建议采用相反的饮食，并可能适应在浑浊的水中或其他低能见度条件下喂养。我们支持Antirrrhopus适应大型脊椎动物猎物，但是我们发现它的头骨比其他直龙对咬力的抵抗力相对较小。鉴于Mongoliensis的高抗咬力恢复，它被认为经常从事清除行为，我们认为，屈龙类群中较高的抗咬力可能反映出对清除而不是新鲜杀死的更大依赖。与蒙古鱼尾科动物的比较表明，像蒙古Velociraptor一样的轻柔讲台是其最接近的共同祖先（Deinonychosauria）的祖先，而Dromaeosaurusalbertensis和Deinononychotirhopusantirrhopus是一种衍生条件。Gobivenatormongoliensis还显示出较高的颌骨机械优势和较低的抗咬合力，但是考虑到假设的牙齿龙与牙龙的生态差异，目前尚不清楚是哪一组，如果是,代表祖先条件。因此，将采样扩展到牙体的未来工作将是无价的，并为早期鸟类的头骨形式和功能的起源提供了急需的背景。这项研究说明了头骨形状和功能指标如何在较低的分类学水平上辨别非禽兽脚类动物的生态学，并确定食肉性进食的变体。
