PLANT EXTINCTION AND RECOVERY DYNAMICS ACROSS THE CRETACEOUS-PALEOGENE TRANSITION IN SOUTHERN SOUTH AMERICA
Open Access
- Author:
- Stiles, Elena
- Graduate Program:
- Geosciences
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 05, 2019
- Committee Members:
- Peter Daniel Wilf, Thesis Advisor/Co-Advisor
Mark E Patzkowsky, Committee Member
Timothy Bralower, Committee Member - Keywords:
- Extinction
Cretaceous
Paleogene
Macrofloras
Recovery
Southern Hemisphere
Patagonia
K-Pg
Paleobotany - Abstract:
- The 66 Ma Cretaceous-Paleogene (K-Pg) mass extinction appears to have been globally heterogeneous for some marine and terrestrial organismal groups. Previous studies on limited Southern Hemisphere K-Pg microfloras show lower extinction percentages and faster-paced recoveries than their Northern Hemisphere counterparts, but no Southern Hemisphere macrofloral turnover studies comparable with the well-constrained analyses of North American (NAM) macrofloras had been possible until now. Through the analysis of over 4,000 dicot leaves from the latest Cretaceous (Maastrichtian) strata of the Lefipán Formation and the early Paleocene (Danian) Salamanca and Peñas Coloradas formations of Argentine Patagonia, this study addresses macrofloral extinction and recovery with a large sample size for the first time in the Southern Hemisphere. Based on a morphotype classification, macrofloral extinction is >90%, and rarefaction analysis showed a ca. 45% drop in diversity across the K-Pg where compositionally homogeneous, low diversity Paleocene floras superseded rich Maastrichtian assemblages. Comparison with rarefied NAM macrofloras shows much higher Patagonian species richness not only in Danian but also Maastrichtian macrofloras, suggesting a deep history of exceptional South American floral diversity before the Paleocene and into the terminal Cretaceous at least. Morphospace analysis of Maastrichtian and Danian leaf assemblages indicates continuity and expansion of leaf types and their underlying ecological and phylogenetic diversity across the boundary despite the lower Danian morphotype richness. Comparison of published palynomorph and taxonomic macrofossil records provides evidence for a low family-level turnover both across the K-Pg and despite the ca. 400 km separating the studied areas of the Lefipán and Salamanca formations. The increase of lobed and toothed morphotypes in the Patagonian Paleocene contrasts with the loss of lobed leaves across the K-Pg in NAM. Further contrasting with Patagonian results, NAM rarefaction analysis shows a ca. 75% drop in diversity across the boundary. Interestingly, leaves with affinity to Lauraceae are a dominant component of Danian macrofloras in Patagonia, a pattern also observed in some NAM floras. The significant macrofloral extinction percentage, drop in rarefied diversity across the K-Pg, and low diversity homogeneous Danian floras are consistent with substantial species-level extinction in Argentine Patagonia broadly following similar patterns to NAM. However, the contrasts arising between Patagonian and NAM macrofloral records in Maastrichtian and Danian standing species richness, and morphological turnover appear to reflect a geographically heterogeneous Northern vs. Southern Hemisphere extinction and recovery pattern as observed in other marine and paleontological records.