3D morphometric analysis of fossil canid skulls contradicts the suggested domestication of dogs during the late Paleolithic

Abstract

Whether dogs were domesticated during the Pleistocene, when humans were hunter-gatherers, or during the Neolithic, when humans began to form permanent settlements and engage in agriculture, remains controversial. Recently discovered Paleolithic fossil skulls, Goyet dated 31,680 +/- 250 YBP and Eliseevichi MAE 447/5298 dated 13,905 +/- 55 YBP, were previously identified as dogs. However, new genetic studies contradict the identification of these specimens as dogs, questioning the validity of traditional measurements used to morphologically identify canid fossil skulls. We employ 3D geometric morphometric analyses to compare the cranial morphology of Goyet and Eliseevichi MAE to that of ancient and modern dogs and wolves. We demonstrate that these Paleolithic canids are definitively wolves and not dogs. Compared to mesaticephalic (wolf-like breeds) dog skulls, Goyet and Eliseevichi MAE, do not have cranial flexion and the dorsal surface of their muzzles has no concavity near the orbits. Morphologically, these early fossil canids resemble wolves, and thus no longer support the establishment of dog domestication in the Paleolithic.

Figure 1. Bivariate plots of Euclidean distance based cranial indices.

(a) Log₁₀ total skull length versus Log₁₀ viscerocranial length, (b) Log₁₀ viscerocranial length versus Log₁₀ greatest palate width (c) Log₁₀ total skull length versus Log₁₀ alveolar length, (d) Log₁₀ viscerocranial length versus Log₁₀ minimum palate width. Convex hulls of dogs, Alaskan wolves, and European wolves are outlined.

Figure 2. PCA of Euclidean distance based cranial indices.

(a) PC1 versus PC3, (b) PC2 versus PC3, (c) PC1 versus PC2. Convex hulls of dogs, Alaskan wolves, and European wolves are outlined.

Figure 3. Bivariate plot of palate width versus total skull length.

Convex hulls of dogs, Alaskan wolves, and European wolves are outlined.

Figure 4. PCA plot of 36 form space coordinates.

(a) 3D plot of PC1, PC2 and PC3, (b) 3D morphs of extremes along PC 1, PC 2 and PC 3. 95% Confidence interval ellipsoids of modern dogs, Alaskan wolves, and European wolves are outlined. Unclassified specimens are labelled separately in this and other figures. A 3D version of this figure is available as Supplementary Figure S1.

Figure 5. 3D surface models of fossil specimens used in this analysis.

(a) Eliseevichi MAE 447/5298, (b) Goyet, (c) Shamanka II, (d) Trou Balleux, (e) Ust'-Belaia. A 3D version of this figure is available as Supplementary Figure S2.

Figure 6. PCA plot of 36 form space coordinates including classified fossil specimens.

(a) 3D plot of PC1, PC2 and PC3, (b) 3D morphs of extremes along PC 1, PC 2 and PC 3. 95% Confidence interval ellipsoids of modern dogs, Alaskan wolves and European wolves are outlined. Unclassified specimens are labelled separately in this and other figures. A 3D version of this figure is available as Supplementary Figure S3.