Miocene ungulates and terrestrial primary productivity: Where have all the browsers gone?
Miocene ungulates and terrestrial primary productivity: Where have all the browsers gone?
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DOI：
10.1073/pnas.97.14.7899
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发表时间：
2000-07-05
影响因子：
11.1
通讯作者：
Theodor, JM
中科院分区：
文献类型：
--
作者：
Janis, CM;Damuth, J;Theodor, JM
在中新世时期[24-5百万年（Ma）]，哺乳动物区系和植被的组成都发生了渐进的变化，这些变化通常被解释为对气候变化的响应。在传统观点中，森林或林地逐渐让位于更开阔的栖息地，随着草原的扩大，放牧（食草）的有蹄类哺乳动物物种取代了浏览（食叶植物）物种。然而，来自北美大平原地区化石组合的数据表明，这种动物群的变化并不像通常认为的那样是食草动物对浏览者的一对一取代。典型的早中新世晚期（17 Ma）化石群落包括非常高数量的食草有蹄类物种，其动物群不能与任何现今群落直接类比。所有有蹄类动物的最大物种丰富度和浏览器的比例稳步下降，有蹄类动物群落通过中新世中期，到目前的水平相媲美的中新世晚期。由此产生的戏剧性的，累积的损失浏览物种构成了一个最强的动物区系信号的晚第三纪（但不是一个单一的“事件”）。我们认为，早中新世浏览器丰富的社区可能反映了较高水平的初级生产力在中新世植被，相当于现今的植被类型相比。观察到的物种丰富度下降可能代表初级生产力的逐渐下降，这与目前的一个假设是一致的，即大气CO2浓度从较高的中新生代值下降到中新世中期。
Progressive changes are observed in both the composition of mammal faunas and vegetation during the Miocene epoch [24-5 mega-annum (Ma)], These changes are usually interpreted as a response to climatic changes. In the traditional view, forests or woodlands gradually gave way to more open habitats, with grazing (grass-eating) ungulate (hoofed) mammal species replacing the browsing (leafy-vegetation-eating) species as grasslands expanded. However, data from fossil assemblages in the Great Plains region of North America show that this faunal change was not a one-for-one replacement of browsers by grazers, as usually thought. Typical late early Miocene (17 Ma) fossil communities included extraordinarily high numbers of browsing ungulate species, comprising a fauna that cannot be directly analogized with any present-day community. Both maximum species richness of all ungulates and the proportion of browsers declined steadily in ungulate communities through the middle Miocene, to levels comparable to those of the present by the late Miocene. The resulting dramatic, cumulative loss of browsing species constitutes one of the strongest faunal signals of the late Tertiary (but was not a single "event"). We suggest that the early Miocene browser-rich communities may reflect higher levels of primary productivity in Miocene vegetation, compared with equivalent present-day vegetation types. The observed decline in species richness may represent a gradual decline in primary productivity, which would be consistent with one current hypothesis of a mid-Miocene decrease in atmospheric CO2 concentrations from higher mid-Cenozoic values.