Comparison of the fine structure of hair in the ancient Lena horse (†Equus lenensis Russanov 1968) and the domestic horse (Equus caballus caballus Linnaeus 1758) of native northern breeds

Using SEM and morphometry, the fine structure of guard hairs and the elements of their medulla were compared in the Lena horse (Equus lenensis) and the domestic horse (E. caballus caballus) of five breeds. A number of features of hair fine structures have been identified, most clearly revealed when comparing horses of the northern (Mezen, Pechora, Yakut) and southern (Arabian, Akhal-Teke) groups of breeds. Seasonal changes in the structure of hair in horses of northern breeds (thickening of the hair medulla and an increase in the volume of its air cavities) indicate an increase in the heat-protecting properties of wool in winter, this being of adaptive significance. Both Pleistocene and recent domestic horses are shown to have developed convergent morphological adaptations of wool to low air temperatures.