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：在中新世早期的当地动物群中，世界范围内的浏览器物种是否“过多”？使用澳大利亚哺乳动物化石记录检验全球假说--加州大学圣巴巴拉分校的克里斯汀·贾尼斯、布朗大学和约翰·达穆斯是否有证据表明，大约1200万年前，全球陆地生态系统发生了以前未被认识到的变化？PI们假设，他们在北美哺乳动物动物群历史上首次观察到的一种惊人的模式，可能是实际上在全球范围内都能观察到的模式。该项目将通过确定澳大利亚化石记录中是否同时发生相同的模式来检验这一假设。以前的研究表明，在1200万年前到1000万年前的北美，许多生态群落中含有数量异常多的食性有蹄类动物(大型食叶草食动物)？这一数字是现代植被可比栖息地的三倍。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的物种数量？当今浏览器生物多样性最高的栖息地。这些哺乳动物动物群的其他成员都没有表现出任何升高或不寻常的生物多样性，而年龄在1200-1000万年前的动物群只显示了“正常”数量的浏览器物种(按照今天的标准)。为什么较老的栖息地有时能够支持今天不可能达到的大量浏览器，目前尚不清楚。然而，有证据表明，1200万年前欧洲和非洲的一些动物群也显示出“太多”的浏览器，这反过来又表明这是一个全球性的原因。这个项目将回答这样一个问题，即澳大利亚有充分记录的哺乳动物化石记录中是否也有过多的浏览器，如果是的话，这种现象是否与北美几乎同时消失。通过对澳大利亚各地博物馆藏品的研究，可以根据牙齿的形态和磨损情况，确定不同时期的鸟类数量。澳大利亚独特的动物群和环境历史将为“浏览器过多”是否在全球范围内发生提供强有力的测试。如果不是，那么我们必须寻找区域或局部原因；但如果全球假说得到支持，那么全球现象就更有可能发生，这些结果将指导和激励随后寻找全球原因的工作。该项目的结果不仅将对全球环境历史和气候变化产生影响，还将对任何试图对1000万年前的动物群进行古生态解释的方法产生影响，这些方法使用现代哺乳动物动物群作为环境替代品。这个项目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.