Were ancient foxes far more carnivorous than recent ones?—Carnassial morphological evidence

Crown shape variation of the first lower molar in the arctic (Vulpes lagopus) and red foxes (Vulpes vulpes) was analyzed using five groups of morphotypes. Carnassial morphologies were compared between the species and between spatially and temporally distant populations: one Late Pleistocene (n = 45) and seven modern populations of the arctic fox (n = 259), and one Late Pleistocene (n = 35) and eight modern populations of the red fox (n = 606). The dentition of Holocene red foxes had larger morphotype variability than that of arctic foxes. The lower carnassials of the red fox kept have some primitive characters (additional cusps and stylids, complex shape of transverse cristid), whereas the first lower molars of the arctic fox have undergone crown shape simplification, with the occlusal part of the tooth undergoing a more pronounced adaptation to a more carnivorous diet. From the Late Pleistocene of Belgium to the present days, the arctic fox’s crown shape has been simplified and some primitive characters have disappeared. In the red fox chronological changes in the morphology of the lower carnassials were not clearly identified. The phyletic tree based on morphotype carnassial characteristics indicated the distinctiveness of both foxes: in the arctic fox line, the ancient population from Belgium and recent Greenland made separate branches, whereas in the red foxes the ancient population from Belgium was most similar to modern red foxes from Belgium and Italy.本研究采用五组形态型（morphotypes）分析了北极狐（Vulpes lagopus）与赤狐（Vulpes vulpes）的第一下臼齿齿冠形态变异情况。研究对比了两物种间以及时空相隔种群间的裂齿（carnassial）形态：其中北极狐涵盖1个晚更新世（Late Pleistocene）种群（样本量n=45）与7个现代种群（n=259），赤狐则涵盖1个晚更新世种群（n=35）与8个现代种群（n=606）。全新世（Holocene）赤狐的齿列形态型变异程度高于北极狐。赤狐的下裂齿保留了部分原始特征，包括额外齿尖、附尖（stylids）以及横脊（transverse cristid）的复杂形态；而北极狐的第一下臼齿则发生了齿冠形态简化，其咬合面（occlusal part）更显著地适应了高度肉食性的食性。自比利时晚更新世至今，北极狐的齿冠形态逐渐简化，部分原始特征消失。赤狐的下裂齿形态并未出现明确的年代学变化。基于裂齿形态型特征构建的系统发育树（phyletic tree）显示两种狐类存在明显分化：北极狐支系中，比利时古种群与现代格陵兰种群各自形成独立分支；而赤狐支系中，比利时古种群与现代比利时及意大利赤狐种群亲缘关系最为相近。