Fossil horses from “Eohippus” (Hyracotherium) to Equus: scaling, Cope's Law, and the evolution of body size
Fossil horses from “Eohippus” (Hyracotherium) to Equus: scaling, Cope's Law, and the evolution of body size
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从“始马兽”（Hyracotherium）到马属的化石马：缩放、科普定律和体型的演变
作者：
B. MacFadden
化石马的体型演变经常被描述为一个逐渐的、渐进的体型增长趋势（科普定律）。利用马属现存马类动物的牙齿和骨骼特征以及已知体质量的马类动物牙齿和骨骼特征的回归方程，估算了40种马化石的体型（实际体质量）。在估计了体型之后，我们计算了已知的祖先和后代化石马物种之间的达尔文（d）形态进化速率。马进化的前半部分（从CA。57 ~ 25 ma）体重在25 ~ 50 kg之间保持相对稳定，进化速率非常慢，为0.003-0.04 d。早中中新世（约1000年）25至10毫安），有一个主要的多样化的体重约75-400公斤和一贯较高的进化率之间的0.04和0.24天。自中新世晚期以来，身体质量普遍增加，在自然种群中最大的是马斯科特（约200米）。500公斤）。因此，对于马，传统的解释是随着时间的推移逐渐增加的身体大小是过于简单化，因为：（1）虽然例外的规则，5的24个物种谱系研究的特点是侏儒症;总的趋势似乎是一个较长的相对停滞期（32 ma），然后是25 ma的多样化和进步（虽然不一定是渐进的）身体大小的变化。
The evolution of body size in fossil horses is frequently depicted as a gradual, progressive trend toward increased body size (Cope's Law). Body size (actually body mass) was estimated for 40 species of fossil horses using dental and skeletal characters and regression equations derived from the same characters in extant species of Equus with known body mass. After body sizes were estimated, rates of morphological evolution, in darwins (d), were calculated between known ancestral and descendant fossil horse species. For the first half of horse evolution (from ca. 57 to 25 ma) body mass remained relatively static between about 25 and 50 kg with very slow evolutionary rates of 0.003–0.04 d. During the early–middle Miocene (from ca. 25 to 10 ma) there was a major diversification of body mass to about 75–400 kg and consistently higher evolutionary rates between 0.04 and 0.24 d. Since the late Miocene, body mass has generally increased with a maximum seen (in natural populations) in Equus scotti (ca. 500 kg) during the middle Pleistocene. Therefore, for horses, the traditional interpretation of gradual increase in body size through time is oversimplified because: (1) although the exception to the rule, 5 of 24 species lineages studied are characterized by dwarfism; and (2) the general trend seems to have been a long period (32 ma) of relative stasis followed by 25 ma of diversification and progressive (although not necessarily gradual) change in body size.