Ways of adaptive changes in claws of digging mammals [Russian]

摘要

The digging activity requires large expenses of energy and is reflected in the structure of claws. Digging animals use their claws differently. One method is loosening of ground. In this case, it is advantageous to have sharp cutting edge of claw and smaller diameter, which is perpendicular to trajectory of movement. When claws move vertically (Meles) the lamina corneas become thicker equally on both sides of phalanx and grow together from below. If the trajectory of movement is directed from above downwards with some inclination sideways, the lateral wall of lamina cornea is thickened. When working, it is erased to a greater degree that leads to sharpening of the claw ventral edge. In this case, the terminal phalanx is symmetric in cross-section, and the sharp edge is formed due to more intensive growth and erasing of the lateral wall of lamina cornea (Prometheomys, Myospalax, Geomys). In other case, the cross-section of the terminal phalanx is asymmetric. The lateral part is more advanced, its horn layer grows actively. This layer is erased making the ventral edge of terminal phalanxes sharper (Chlamyphorus, Chrysochloris, Notoryctes). If the digging trajectory is horizontal, claws are flattened. The sharp edges are formed on the lateral side of the 5(th) and 4(th) fingers, on the medial side of the 1(st) and 2(nd) ones, and from both sides, on the 3(d) finger (Tachydlossus). Destruction of walls of termite nests also requires strengthening of claws. in one case it results in bifurcation of terminal phalanx with formation of a threefold beam (Manis), in the other one, the internal part of lamina solearis becomes more thickened (Myrmecophaga). In the animals, which do not loose, but pull out the ground, claws are flat without sharp edges (Talpidae).