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

Abstract

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.

Fig 1. Geographic distribution of the recent and fossil samples of the arctic Vulpes lagopus and red foxes Vulpes vulpes used in the study.

Black rhomb–recent populations of the arctic fox measured by Szuma (2011), empty rhomb–fossil populations of the arctic fox measured by Szuma for the study, grey circle–recent populations of the red fox measured by Szuma (2011); empty circle–fossil population of the red fox measured by Szuma for the study. Information about the samples can be found in Table 1.

Fig 2. Graphic depiction of morphological variation of the first lower molar (M₁) in the red and arctic foxes.

Group K–M₁ in lateral view, lingual side; group L–M₁ in lateral view, buccal side; group P, R, S–distal part of M₁ (talonid) in occlusal view. Definitions of the morphotypes, and morphotype variants are listed in S4 Table.

Fig 3. Share of morphotypes in fossil and recent populations of the arctic fox.

Numerals in each part of the pie chart are the numbers of specimens with the morphotypes. Illustrations of the tooth variants and morphotypes are shown in Fig 2. Information about the samples can be found in Table 1.

Fig 4. Share of morphotypes in fossil and recent populations of the red fox.

Numerals in each part of the pie chart are the numbers of specimens with the morphotypes. Illustrations of the tooth variants and morphotypes are shown in Fig 2. Information about the samples can be found in Table 1.

Fig 5. Comparison of median values for length, width, and size proportion of M₁ between various K group morphotypes in the arctic fox with and without population division.

Illustrations of group K morphotypes are shown in Fig 2. Information about the samples can be found in Table 1.

Fig 6. Comparison of median values for length, width, and size proportion of M₁ between various group K morphotypes in the red fox with and without population division.

Illustrations of group K morphotypes are shown in Fig 2. Information about the samples can be found in Table 1.

Fig 7. Comparison of median values for length, width, and size proportion of M₁ between various group L morphotypes in the arctic fox with and without population division.

Illustrations of group L morphotypes are shown in Fig 2. Information about the samples can be found in Table 1.

Fig 8. Comparison of median values for length, width, and size proportion of M₁ between various group L morphotypes in the red fox with and without population division.

Illustrations of group L morphotypes are shown in Fig 2 Information about the samples can be found in Table 1.

Fig 9. Comparison of median values for length, width, and size proportion of M₁ between various group P morphotypes in the arctic fox with and without population division.

Illustrations of group P morphotypes are shown in Fig 2. Information about the samples can be found in Table 1.

Fig 10. Comparison of median values for length, width, and size proportion of M₁ between various group P morphotypes in the red fox with and without population division.

Illustrations of P group morphotypes are shown in Fig 2. Information about the samples can be found in Table 1.

Fig 11. Comparison of median values for length, width, and size proportion of M₁ between various group R morphotypes in the red fox with and without population division.

Illustrations of group R morphotypes are shown in Fig 2. Information about the samples can be found in Table 1.

Fig 12. Comparison of median values for length, width, and size proportion of M₁ between various S group morphotypes in the red fox with and without population division.

Illustrations of group S morphotypes are shown in Fig 2. Information about the samples can be found in Table 1.

Fig 13. Distribution of the populations of the arctic and red foxes in a two-dimensional plane based on the morphotype variations of the first lower molar.

Black rhomb–recent populations of the arctic fox, empty rhomb–fossil populations of the arctic fox, grey circle–recent populations of the red fox, empty circle–fossil population of the red fox. Information about the samples can be found in Table 1.

Fig 14. Agglomeration of the recent and fossil populations of the arctic and red foxes constructed by the Ward method and Manhattan distances using the percentage shares of the morphotypes of the first lower molar.