This study considered possible sexual dimorphism in the relative lengths of the second, third and fourth digits (digit ratio), in calves. Furthermore, a different length of the bone structures of the third (3D) and of the fourth (4D) digits has been examined as an evolutionary adaptation to locomotion on soft ground. The length of the digital bones of the right fore-limb of 33 females and 15 male calves was measured in vivo using a portable X-ray machine. The vestigial structure of the second digit (2D), and 3D and 4D, from metacarpus to the third phalanx were considered in a mixed model, as well as some ratios between 2D and different parts of 3D or 4D (2D:3D and 2D:4D). A covariate for the mean finger length was considered for digit ratios to control for possible biases due to shape allometry. Shorter first phalanx and trotter were found in 3D than in 4D, and the reverse for the third phalanx. The 2D was significantly shorter in females, as well as the second phalanges of 3D and 4D. Significant sex differences in 2D:3D and 2D:4D were found for some digit parts of 3D and 4D and for the first phalanges of 3D:4D. These ratios were always shorter in females, in contrast to that found in most mammals. The asymmetry between 3D and 4D could mean a functional adaptation for locomotion. Sex differences in 2D:4D and 3D:4D were found, but with a reverse pattern than in most mammal species (males > females rather than males < females). In this regard digit ratio in calves was similar to that of Old World monkeys. This study is the first investigation of digit ratio in Ungulates, whose limbs differ from the limbs of most mammals, maintaining five digits. The reverse pattern of sex differences (digit ratios: males> females) could be due to the peculiar nature of the vestigial dewclaw of 2D and to the hormone patterns acting on this digit during development, but further research is required around this topic.

中文翻译：

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小牛四肢的数字比例和长度不对称

该研究考虑了犊牛第二、第三和第四指的相对长度（指比）可能存在的性别二态性。此外，第三 (3D) 和第四 (4D) 指骨结构的不同长度已被研究作为对软地面运动的进化适应。使用便携式 X 光机在体内测量了 33 只雌性和 15 只雄性小牛的右前肢数字骨的长度。在混合模型中考虑了第二指 (2D) 和 3D 和 4D 的残留结构，从掌骨到第三指骨，以及 2D 与 3D 或 4D 不同部分之间的一些比例（2D：3D 和 2D： 4D）。平均手指长度的协变量被考虑用于手指比率，以控制由于形状异速生长可能导致的偏差。在 3D 中发现的第一个方阵和猪蹄比在 4D 中更短，而第三个方阵则相反。女性的 2D 以及 3D 和 4D 的第二指骨明显更短。对于 3D 和 4D 的某些数字部分以及 3D:4D 的第一指骨，发现了 2D:3D 和 2D:4D 的显着性别差异。与大多数哺乳动物相比，雌性的这些比率总是较短。3D 和 4D 之间的不对称可能意味着对运动的功能适应。发现了 2D:4D 和 3D:4D 的性别差异，但与大多数哺乳动物物种的模式相反（雄性 > 雌性而不是雄性 < 雌性）。在这方面，小牛的手指比例与旧世界猴子的数字比例相似。这项研究是对有蹄类动物手指比例的首次调查，它们的四肢与大多数哺乳动物的四肢不同，保持五位数。性别差异的反向模式（手指比例：男性>女性）可能是由于 2D 残留狼爪的特殊性质以及在发育过程中作用于该数字的激素模式，但需要围绕这一主题进一步研究。