盡管研究人員被警告不要看某些馬的口腔,，但他們還是收集了有關在以往的5550萬年中，北美的馬的牙齒進化的大量的數(shù)據(jù),。 一項新的報告顯示,，牙齒磨損度（這是對磨牙的尖利度及鏟磨度的描繪，人們可用其來測量一匹馬口腔中其磨牙及其它牙齒因為食物而磨損的程度）的變化趨勢與古時候全球氣溫冷卻事件及植被的變化有關,。 當馬在跨越千年時間的演化中,，它們的磨牙緩慢地由低冠磨牙變化成為高冠磨牙；研究人員認為這一事實與草原的擴大及靠近地面的對牙齒磨損度更大的食物有關聯(lián),。 現(xiàn)在,，Matthew Mihlbachler及其同事說，在演化進程中牙齒磨損度的增加確實與這種磨牙高度的增加有關聯(lián),。 但是,，古時候大多數(shù)的馬的種群顯示了其食物磨損性的高度可變性，這提示牙冠高度增加的選擇壓力在大多數(shù)的時間可能都是弱的,，即馬在其整個進化中由于獲取食物方便而生活得相當輕松,。 但是，研究人員確實發(fā)現(xiàn),，馬在其整個歷史中有某些時候的進食草的壓力一定很高,，其中包括在中新世早期（即馬亞科剛出現(xiàn)之前），當時馬亞科動物中才真正開始流行那些高冠磨牙。（生物谷Bioon.com）
生物谷推薦原文出處：
Science DOI: 10.1126/science.1196166
Dietary Change and Evolution of Horses in North America
Matthew C. Mihlbachler1,2,*, Florent Rivals3, Nikos Solounias1,2, and Gina M. Semprebon4
Abstract
The evolution of high-crowned molars among horses (Family Equidae) is thought to be an adaptation for abrasive diets associated with the spread of grasslands. The sharpness and relief of the worn cusp apices of teeth (mesowear) are a measure of dietary abrasion. We collected mesowear data for North American Equidae for the past 55.5 million years to test the association of molar height and dietary abrasion. Mesowear trends in horses are reflective of global cooling and associated vegetation changes. There is a strong correlation between mesowear and crown height in horses; however, most horse paleopopulations had highly variable amounts of dietary abrasion, suggesting that selective pressures for crown height may have been weak much of the time. However, instances of higher abrasion were observed in some paleopopulations, suggesting intervals of stronger selection for the evolution of dentitions, including the early Miocene shortly before the first appearance of Equinae, the horse subfamily in which high-crowned dentitions evolved.
