Abstract

Paleoclimatic archives preserved in bioapatite provide long-term temporal records of climatic change and allow us to explore how climate may have affected faunal and floral changes through time. Among the most comprehensively debated research questions is the question of C₄ grassland expansion and its effects on community structure and dynamics. Here, we present compiled datasets of carbon isotopes from fossil tooth enamel and paleosol to evaluate how C₄ grasslands expanded and its apparent causes. The C₄ expansion has been argued to be around ca 8–7 Ma in the Siwalik sub-Group of Pakistan, but the later stages of C₃/C₄ proportion shifts on the Siwalik floodplains are less understood. We found that although C₄ expansion occurred during the late Miocene, C₃ vegetation never entirely disappeared but was persisted in pockets on floodplain up to the present, as indicated by the C₃ diet consumed by some herbivores. The expansion was further modulated by the microclimate in different regions. The same scenario can be seen in East Africa, South America and low-latitude North America where C₄ grasslands expanded rapidly in late Miocene most likely owing to decrease in global pCO₂. By contrast, C₄ plants did not expand in high-latitude North America and Palearctic regions during the past ca 17 Ma. Thus, we assume that C₄ plants expanded at low latitudes during the late Miocene owing to one major global factor (decreased pCO₂) and perhaps other local microclimatic factors like paleofires.

1. KEY POINTS

2. During the late Miocene, low-latitude regions experienced a climatic change followed by a transition from C₃ to C₄ vegetation.

3. The timing of C₄ expansion was not synchronous across all the regions and was controlled by global and microclimatic factors.

4. Although C₄ vegetation expanded after the late Miocene, C₃ vegetation did not disappear and was present at the edges of floodplains.

5. The new adaptive physiologies (like hypsodonty) in faunal elements were evolutionary adaptive responses toward new vegetational types available.

摘要

保存在生物磷灰石中的古气候档案提供了气候变化的长期时间记录，使我们能够探索气候可能如何影响动植物随时间的变化。C ₄草地扩张及其对群落结构和动态的影响是争论最广泛的研究问题之一。在这里，我们展示了来自化石牙釉质和古土壤的碳同位素汇编数据集，以评估 C ₄草原如何扩张及其明显原因。的C ₄扩张一直争论是围绕CA 8-7马云在巴基斯坦的西瓦利克子组，但是C的后期阶段₃ / C ₄对 Siwalik 洪泛区的比例变化了解较少。我们发现，虽然 C ₄扩张发生在中新世晚期，但 C ₃植被从未完全消失，而是一直存在于漫滩上的口袋中，直到现在，正如一些食草动物消耗的 C ₃饮食所表明的那样。不同地区的小气候进一步调节了扩张。在东非、南美洲和北美洲低纬度地区也可以看到同样的情况，这些地区的 C ₄草原在中新世晚期迅速扩张，最有可能是由于全球p CO _{2 的}减少。相比之下，C ₄在过去的大约17 Ma期间，植物没有在高纬度北美和古北地区扩张。因此，我们假设 C ₄植物在中新世晚期在低纬度扩张，这是由于一个主要的全球因素（p CO ₂减少）和其他局部小气候因素（如古火）。

1. 关键点

2. 在中新世晚期，低纬度地区经历了气候变化，随后是从 C ₃到 C ₄植被的过渡。

3. C ₄扩张的时间在所有地区并不同步，并受全球和小气候因素的控制。

4. 尽管C ₄植被在晚中新世之后有所扩张，但C ₃植被并未消失，而是存在于漫滩边缘。

5. 动物区系元素中新的适应性生理学（如 hypsodonty）是对可用的新植被类型的进化适应性反应。