COLLABORATIVE RESEARCH: Were there "too many" browser species worldwide in local faunas of the Early Miocene? Testing a global hypothesis using the Australian fossil mammal record

合作研究：中新世早期的本地动物群中是否有“太多”的浏览器物种？布朗大学的Christine Janis和加州大学圣巴巴拉分校的John Damuth利用澳大利亚的哺乳动物化石记录验证了一个全球性的假设，是否有证据表明大约1200万年前陆地生态系统发生了一场以前未被认识到的全球性变化？科学家们假设，他们在北美哺乳动物群历史上首次观察到的一个惊人模式，可能在全球范围内都能观察到。这个项目将通过确定同样的模式是否同时发生在澳大利亚的化石记录中来验证这一假设。先前的研究表明，在1200万到1000万年前的北美，许多生态群落中有大量的食草有蹄类动物（大型食叶食草动物）。这一数量是现代植物栖息地的三倍。事实上，有些地方的浏览器物种数量甚至超过了现代热带雨林。现今的栖息地有最高的生物多样性的浏览器。这些哺乳动物群的其他成员没有表现出任何提高或不寻常的生物多样性，年龄小于1200万至1000万年的动物群只显示出“正常”数量的浏览器物种（以今天的标准）。为什么旧的栖息地有时能够支持今天不可能的大量浏览器，目前尚不清楚。然而，有证据表明，1200万年前的一些欧洲和非洲动物也显示出“太多”的浏览者，这反过来又表明了一个全球性的原因。这个项目将回答这样一个问题：在澳大利亚有充分记录的哺乳动物化石记录中，是否也有“太多”的浏览者，如果是的话，这种现象是否与北美的消失时间差不多。对澳大利亚各地博物馆藏品的研究，将根据牙齿的形态和磨损程度，确定不同时期浏览器物种的数量。澳大利亚独特的动物群和环境历史将为“浏览者过多”是否是全球性现象提供有力的检验。如果不是，那么我们必须寻找区域性或地方性的原因；但是，如果全球假说得到支持，那么全球现象就更有可能出现，这些结果将指导和激励后续对全球原因的研究。该项目的结果不仅将对全球环境史和气候变化产生影响，而且对任何试图用现代哺乳动物群体作为环境代理来解释1000万年以上的动物群体的古生态方法也有影响。这将是一个新的国际合作项目，将有学生和博士后研究人员参与。

COLLABORATIVE RESEARCH:Were there "too many" browser species worldwide in local faunas of the Early Miocene? Testing a global hypothesis using the Australian fossil mammal record - Christine Janis, Brown University and John Damuth, University of California, Santa BarbaraIs there evidence for a previously unrecognized worldwide change in terrestrial ecosystems approximately 12 million years ago? The PIs hypothesize that a striking pattern that they observed first in the history of the mammal faunas of North America may be one that is actually observable throughout the globe. This project will test this hypothesis by determining whether the same pattern occurred contemporaneously in the fossil record of Australia. Previous research showed that before 12-10 million years ago in North America, many ecological communities contained exceptionally high numbers of species of browsing ungulates (large leaf-eating herbivores) ? up to three times the numbers seen in vegetationally comparable modern-day habitats. In fact, the numbers of browser species in some places exceeded even those for modern tropical rainforests ? the present-day habitats with the highest biodiversity of browsers. No other members of these mammal faunas showed any elevated or unusual biodiversity, and faunas younger than 12-10 million years show only "normal" numbers of browser species (by today's standards). Why the older habitats were sometimes able to support what today would be impossibly high numbers of browsers is currently unknown. However, evidence suggests that some European and African faunas from before 12 million years ago also showed "too many" browsers, which in turn suggests a global cause. This project will answer the question of whether there were also "too many" browsers in the well-documented mammalian fossil record of Australia, and, if so, whether this phenomenon disappeared at about the same time as it did in North America. Study of museum collections from Australian localities will allow determination of the numbers of browser species at different times, based on morphology and wear of the teeth. Australia's distinct fauna and environmental history will provide a robust test of whether "too many browsers" was a global occurrence. If it wasn't, then we must look for regional or local causes; but if the global hypothesis is supported then a worldwide phenomenon becomes more likely and these results will guide and motivate the subsequent search for a global cause. The project's results will have implications not only for global environmental history and climate change, but also for any methods that attempt paleoecological interpretations for faunas older than 10 million years that use modern mammal faunas as an environmental proxy. This project will be a new international collaboration and will involve students and postdoctoral researchers.