Paleoclimatic and vegetational change in the Siwalik sub-Group of Pakistan and its contemporary geographic regions: a stable isotope perspective

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.

KEY POINTS

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

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

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

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

Keywords:

• carbon isotopes
• Indian region
• East Africa
• South America
• North America
• Europe
• paleodiet

Acknowledgements

The authors are thankful to Michele Morgan (Harvard University) for providing the carbon and oxygen isotope datasets for the Siwalik sub-Group of Pakistan. We are thankful to Dr. Larry Flynn (HARVARD University) for his insightful review and comments. The handling editor, Anita Andrew is thanked for overall correction of the draft and guidance throughout the publication process. This work is a part of PhD thesis of Muhammad Tahir Waseem, which was supported by the Higher Education Commission, Pakistan.

Data   availability

A compendium of new and published data is available in the supplementary papers at https://doi.org/10.1080/08120099.2021.1893221.

Additional information

Funding

The funding for the project was provided by Higher Education Commission, Pakistan to Muhammad Tahir Waseem vide offer no. 15-28107-2BS3-243.