Department of Biology and Burke Museum of Natural History and Culture, University of Washington, Seattle, Washington 98195, USA.
Nat Commun. 2013;4:1478. doi: 10.1038/ncomms2508.
The evolution of high-crowned cheek teeth (hypsodonty) in herbivorous mammals during the late Cenozoic is classically regarded as an adaptive response to the near-global spread of grass-dominated habitats. Precocious hypsodonty in middle Eocene (∼38 million years (Myr) ago) faunas from Patagonia, South America, is therefore thought to signal Earth's first grasslands, 20 million years earlier than elsewhere. Here, using a high-resolution, 43-18 million-year record of plant silica (phytoliths) from Patagonia, we show that although open-habitat grasses existed in southern South America since the middle Eocene (∼40 Myr ago), they were minor floral components in overall forested habitats between 40 and 18 Myr ago. Thus, distinctly different, continent-specific environmental conditions (arid grasslands versus ash-laden forests) triggered convergent cheek-tooth evolution in Cenozoic herbivores. Hypsodonty evolution is an important example where the present is an insufficient key to the past, and contextual information from fossils is vital for understanding processes of adaptation.
晚新生代食草哺乳动物中高冠颊齿（高齿冠）的进化，经典地被认为是对以草为主的栖息地在全球范围内的扩散的一种适应性反应。因此，人们认为南美洲巴塔哥尼亚始新世中期（约 3800 万年前）动物群中早熟的高齿冠现象标志着地球第一批草原的出现，比其他地方早了 2000 万年。在这里，我们利用来自巴塔哥尼亚的分辨率为 43-1800 万年的植物硅质（植硅体）的高分辨率记录，表明尽管开阔生境的草在始新世中期（约 4000 万年前）就已经存在于南美洲南部，但在 4000 万至 1800 万年前，它们只是森林生境中次要的植物组成部分。因此，明显不同的、具有大陆特异性的环境条件（干旱草原与富含灰烬的森林）引发了新生代食草动物趋同的颊齿进化。高齿冠进化是一个重要的例子，它表明现在是过去的一个不充分的关键，并且来自化石的上下文信息对于理解适应过程至关重要。
