Curth Stefan, Fischer Martin S, Kupczik Kornelius
Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universität, Erbertstrasse 1, 07743 Jena, Germany; Max Planck Weizmann Center for Integrative Archaeology and Anthropology, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany.
Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universität, Erbertstrasse 1, 07743 Jena, Germany.
Ann Anat. 2017 Nov;214:53-62. doi: 10.1016/j.aanat.2017.08.003. Epub 2017 Sep 1.
The temporomandibular joint (TMJ) conducts and restrains masticatory movements between the mammalian cranium and the mandible. Through this functional integration, TMJ morphology in wild mammals is strongly correlated with diet, resulting in a wide range of TMJ variations. However, in artificially selected and closely related domestic dogs, dietary specialisations between breeds can be ruled out as a diversifying factor although they display an enormous variation in TMJ morphology. This raises the question of the origin of this variation. Here we hypothesise that, even in the face of reduced functional demands, TMJ shape in dogs can be predicted by skull form; i.e. that the TMJ is still highly integrated in the dog skull. If true, TMJ variation in the dog would be a plain by-product of the enormous cranial variation in dogs and its genetic causes. We addressed this hypothesis using geometric morphometry on a data set of 214 dog and 60 wolf skulls. We digitized 53 three-dimensional landmarks of the skull and the TMJ on CT-based segmentations and compared (1) the variation between domestic dog and wolf TMJs (via principal component analysis) and (2) the pattern of covariation of skull size, flexion and rostrum length with TMJ shape (via regression of centroid size on shape and partial least squares analyses). We show that the TMJ in domestic dogs is significantly more diverse than in wolves: its shape covaries significantly with skull size, flexion and rostrum proportions in patterns which resemble those observed in primates. Similar patterns in canids, which are carnivorous, and primates, which are mostly frugivorous imply the existence of basic TMJ integration patterns which are independent of dietary adaptations. However, only limited amounts of TMJ variation in dogs can be explained by simple covariation with overall skull geometry. This implies that the final TMJ shape is gained partially independently of the rest of the skull.
颞下颌关节（TMJ）传导并限制哺乳动物颅骨与下颌骨之间的咀嚼运动。通过这种功能整合，野生哺乳动物的颞下颌关节形态与饮食密切相关，导致颞下颌关节出现广泛的变异。然而，在经过人工选择且亲缘关系密切的家犬中，尽管它们的颞下颌关节形态存在巨大差异，但品种间的饮食特化可被排除为多样化因素。这就引发了这种变异起源的问题。在此我们假设，即使面对功能需求降低的情况，犬类的颞下颌关节形状仍可通过颅骨形态来预测；也就是说，颞下颌关节在犬类颅骨中仍高度整合。如果这一假设成立，那么犬类颞下颌关节的变异将是犬类巨大颅骨变异及其遗传原因的一个纯粹副产品。我们使用几何形态测量学方法，对214个犬类和60个狼类颅骨的数据集进行了研究。我们在基于CT的分割图像上数字化了颅骨和颞下颌关节的53个三维地标点，并比较了（1）家犬和狼类颞下颌关节之间的变异（通过主成分分析），以及（2）颅骨大小、弯曲度和吻部长度与颞下颌关节形状的协变模式（通过质心大小对形状的回归分析和偏最小二乘分析）。我们发现，家犬的颞下颌关节比狼类的显著更多样化：其形状与颅骨大小、弯曲度和吻部比例显著协变，这些模式与在灵长类动物中观察到的相似。食肉的犬科动物和大多食果的灵长类动物中出现的类似模式，意味着存在独立于饮食适应的基本颞下颌关节整合模式。然而，犬类颞下颌关节的变异中只有有限部分可通过与整体颅骨几何形状的简单协变来解释。这意味着颞下颌关节的最终形状部分独立于颅骨的其他部分而形成。
