Abstract：
Dogs are animals with strong bite force. This strong bite mechanism has led to significant changes in the skeletal system such as fossa masseterica. It can be thought that one side is used more than the other side in chewing and is related to the preference of using the same side\'s hand, eye and foot. In the study, directional asymmetry and fluctuating asymmetry, which occurs as a result of chewing asymmetry, were examined on the first molar teeth and the fossa masseterica in 85 dog mandibles including a wide diversity of morphotypes. The association of high PC1 values for directional asymmetry with a pronounced cranial index, as evident in breeds like Pekingese, Pomeranian and Bulldog, indicates a potential evolutionary or selective breeding trend favouring brachycephaly. On the contrary, guardian breeds like the German shepherd and Bernese mountain dog, which typically require strong jaws for their roles, showcased reduced PC1 values, which might be related to their functional morphology. Similarly, the PCA results for the first molar teeth shape variations also highlighted the influence of cranial shape, with boxer dogs displaying notably higher PC1 values. The fluctuating asymmetrical distributions provided valuable insights into individualistic variations. Interestingly, no specific breed distribution trend was observed for these asymmetries, indicating a more individual-based variation rather than breed-based. It is essential to note that while these results provide valuable insights, further studies are required to understand the underlying causes better. Factors like genetic variations, developmental processes, dietary habits and external environmental factors could play pivotal roles in these observed morphological differences.
摘要：
狗是咬力很强的动物。这种强大的咬合机制导致了骨骼系统的显着变化，例如咬肌窝。可以认为，一侧比另一侧在咀嚼中使用更多，并且与使用同一侧的手的偏好有关，眼睛和脚。在研究中,方向不对称和波动不对称，这是由于咀嚼不对称而发生的，在85只狗下颌骨中的第一磨牙和咬窝上进行了检查，其中包括多种形态类型。方向不对称的高PC1值与明显的颅骨指数的关联，在像北京这样的品种中很明显，波美拉尼亚和斗牛犬,表明潜在的进化或选择性育种趋势有利于短头畸形。相反,监护人的品种像德国牧羊犬和伯尔尼山犬，他们的角色通常需要强壮的下巴，展示了降低的PC1值，这可能与它们的功能形态有关。同样，第一磨牙形状变化的PCA结果也突出了颅骨形状的影响，拳击手犬的PC1值明显更高。波动的不对称分布提供了对个人主义变化的宝贵见解。有趣的是,对于这些不对称性，没有观察到特定的品种分布趋势，表明更多的是基于个体的变异，而不是基于品种的变异。重要的是要注意，虽然这些结果提供了有价值的见解，需要进一步的研究来更好地了解根本原因。遗传变异等因素，发展过程，饮食习惯和外部环境因素可能在这些观察到的形态差异中起关键作用。
