Source: AGU Advances
The open habitat transition (OHT) in west-central North America has been explained as the result of climate change, but until now evidence has mostly relied on the vegetation record itself. Kukla et al.  compiled phytolith and δ18O data of clays and pedogenic carbonates to analyze shifts in precipitation and vegetation over the Cenozoic in Western North America. They interpret a shift in the difference between clay and carbonate δ18O that corresponds with the timing of the open habitat transition to reflect a change in precipitation seasonality. Specifically, they suggest a decrease in the amount of wintertime precipitation and increased aridity best fits the available data, and further speculate that uplift of the Cascades could have triggered these precipitation changes. These hypotheses will spur further investigation into this important ecological change.
Citation: Kukla, T., Rugenstein, J. K. C., Ibarra, D. E., Winnick, M. J., Strömberg, C. A. E., & Chamberlain, C. P. . Drier winters drove Cenozoic open habitat expansion in North America. AGU Advances, 3, e2021AV000566. https://doi.org/10.1029/2021AV000566
—Susan Trumbore, Editor in Chief, AGU Advances