Department of Geology, University of Helsinki, P.O. Box 64, FIN-00014, Finland.
Evolution. 2010 Feb 1;64(2):398-408. doi: 10.1111/j.1558-5646.2009.00830.x. Epub 2009 Sep 7.
One of the classic examples of faunal turnover in the fossil record is the Miocene transition from faunas dominated by anchitheriine horses with low-crowned molar teeth to faunas with hipparionine horses characterized by high-crowned teeth. The spread of hipparionine horses is associated with increased seasonality and the expansion of open habitats. It is generally accepted that anchitheriine horses did not display an evolutionary increase in tooth crown height prior to their extinction. Nevertheless, to test whether anchitheriines showed any changes interpretable as adaptation to local conditions, we analyzed molar teeth from multiple populations of Anchitherium in three dimensions. Our results show differences in tooth morphology that suggest incipient hypsodonty in Spain, the first region experiencing increasingly arid conditions in the early Miocene of Europe. Furthermore, analyses of tooth wear show that Spanish specimens cluster with present ungulates that eat foliage together with grasses and shrubs, whereas German specimens cluster with present-day ungulates that eat mostly foliage. Taken together, even a taxon such as Anchitherium, with a long and successful history of forest adaptation, did respond to regional environmental changes in an adaptive manner.
化石记录中动物群更替的一个经典例子是中新世从以低冠臼齿为主的安琪氏马动物群向以高冠齿为特征的三趾马动物群的转变。三趾马的扩散与季节性增强和开阔生境的扩展有关。人们普遍认为，安琪氏马在灭绝之前并没有表现出牙齿冠高的进化增加。然而，为了检验安琪氏马是否表现出任何可解释为适应当地条件的变化，我们对来自西班牙、德国的多个安琪氏马种群的臼齿进行了三维分析。我们的研究结果表明，在欧洲早中新世西班牙首次经历干旱条件逐渐增强的地区，牙齿形态存在差异，这表明出现了低冠齿向高冠齿演化的初期迹象。此外，牙齿磨损分析表明，西班牙标本与现今以草和灌木为食的食叶动物聚在一起，而德国标本则与现今以食叶为主的有蹄类动物聚在一起。总的来说，即使是像安琪氏马这样在森林环境中具有悠久而成功适应历史的分类群，也以适应的方式对区域性环境变化做出了响应。
