Cretaceous–Paleogene plant extinction and recovery in Patagonia

Elena Stiles,Ari Iglesias,Peter Wilf,María A Gandolfo,N Rubén Cúneo

doi:10.1017/pab.2020.45

Abstract

AbstractThe Cretaceous–Paleogene (K/Pg) extinction appears to have been geographically heterogeneous for some organismal groups. Southern Hemisphere K/Pg palynological records have shown lower extinction and faster recovery than in the Northern Hemisphere, but no comparable, well-constrained Southern Hemisphere macrofloras spanning this interval had been available. Here, macrofloral turnover patterns are addressed for the first time in the Southern Hemisphere, using more than 3500 dicot leaves from the latest Cretaceous (Maastrichtian) and the earliest Paleocene (Danian) of Argentine Patagonia. A maximum ca. 90% macrofloral extinction and ca. 45% drop in rarefied species richness is estimated across the K/Pg, consistent with substantial species-level extinction and previously observed extirpation of host-specialized leaf mines. However, prior palynological and taxonomic studies indicate low turnover of higher taxa and persistence of general floral composition in the same sections. High species extinction, decreased species richness, and homogeneous Danian macrofloras across time and facies resemble patterns often observed in North America, but there are several notable differences. When compared with boundary-spanning macrofloras at similar absolute paleolatitudes (ca. 50°S or 50°N) from the Williston Basin (WB) in the Dakotas, both Maastrichtian and Danian Patagonian species richnesses are higher, extending a history of elevated South American diversity into the Maastrichtian. Despite high species turnover, our analyses also reveal continuity and expansion of leaf morphospace, including an increase in lobed and toothed species unlike the Danian WB. Thus, both Patagonian and WB K/Pg macrofloras support a significant extinction event, but they may also reflect geographically heterogeneous diversity, extinction, and recovery patterns warranting future study.

Highlights

The devastating environmental consequences of the end-Cretaceous bolide impact affected both marine and terrestrial organisms (e.g., Alvarez et al 1980; Prinn and Fegley 1987; Robertson et al 2013; Vellekoop et al 2014; Tyrrell et al 2015; Artemieva and Morgan 2017; Brugger et al 2017)
While acknowledging work on diverse Paleocene floras from the more southerly Denver and San Juan basins (Johnson and Ellis 2002; Flynn and Peppe 2019; Lyson et al 2019), we focus on the floras of the Williston Basin (WB) for comparison, because they come from similar absolute paleolatitudes to our samples, contain both Cretaceous and Paleocene floras that are well sampled in a single area, and remain the best-sampled and described boundary-spanning K/Pg macrofloras of North America (NAM)
Our results suggest that the rich Cenozoic macrofloras of Patagonia carry a legacy of rich Cretaceous floras, as well as significantly earlier recovery of Paleocene species richness resulting from the persistence of most higher taxonomic levels (Supplementary Tables 1, 2)

Summary

Introduction

The devastating environmental consequences of the end-Cretaceous bolide impact affected both marine and terrestrial organisms (e.g., Alvarez et al 1980; Prinn and Fegley 1987; Robertson et al 2013; Vellekoop et al 2014; Tyrrell et al 2015; Artemieva and Morgan 2017; Brugger et al 2017). Several plant and vertebrate groups that had been known only from Mesozoic localities in the Northern Hemisphere, have been reported in Cenozoic Southern Hemisphere deposits suggesting that they survived the K/Pg in southern latitudes (Case and Woodburne 1986; Pascual et al 1992; Bonaparte et al 1993; Goin et al 2006, 2012; McLoughlin et al 2008, 2011; Gelfo et al 2009; Sterli and de la Fuente 2019) Proposed explanations for this geographic heterogeneity (Jiang et al 2010; Donovan et al 2016, 2018) have referenced increased distance from the Mexican impact site (Schulte et al 2010), oceanic buffering of impact winter temperatures in the Southern Hemisphere (Bardeen et al 2017; Tabor et al 2020), and a bolide impact angle that would have directed most ejecta and debris northward (Schultz and D’Hondt 1996)

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