Morphospace analysis of Cretaceous-Paleogene leaves in Argentine Patagonia reveals rapid shift in morphospace occupation, cooling, and stable but diverse Danian assemblages

ARI IGLESIAS; STILES, E.; GANDOLFO, M. A.; WILF P.; CÚNEO RUBEN

Minnesota

Congreso; Botany 2018 Thriving with Diversity; 2018

Botanical Society of America

The response of Southern Hemisphere floras to the Cretaceous-Paleogene (K-Pg) meteoriteimpact and mass extinction 66 million years ago is poorly understood compared to theNorthern Hemisphere. The catastrophic atmospheric and environmental consequences ofthis worldwide major event resulted in extinction rates of 30% for microfloras and 57% formacrofloras in the western interior of North America where the vast majority of K-PgNorthern Hemisphere localities is reported. Leaf collections including over 4,000 specimensfrom well-dated strata of the latest Cretaceous (Maastrichtian) Lefipán Fm. (66-67 Ma) andearliest Paleogene (Danian) Salamanca and Peñas Coloradas fms. (65.7-62.2 Ma) in ArgentinePatagonia offer a unique opportunity to quantify macrofloral K-Pg turnover for the first timein the Southern Hemisphere. Morphospace analysis is used to search for possible survivorpairs and track changes in morphological diversity across the K-Pg boundary. Eachmorphotype in the Maastrichtian-Danian collection is described by a set of discrete leafarchitectural characters summarizing its shape, size, and venation patterns. This dataset isplotted into a multivariate morphospace where the pairwise dissimilarity betweenmorphotypes can be observed as the graphical distance between them. The ordinationdistances between morphotypes in the space are used not only to narrow down the possiblesurvivor pairs but to track changes in morphological diversity across the K-Pg boundary.Morphospace analysis indicates that age is a strong factor, with Maastrichtian and Danianleaves occupying distinct morphological spaces and higher morphological diversity in theDanian following the K-Pg. Further inspection of this pattern reveals that untoothed andunlobed leaves dominate in the Maastrichtian, whereas toothed and lobed leaves dominatein the Danian. The increased proportion of lobed and toothed leaves in the early Danianindicates cooler temperatures than in the terminal Maastrichtian. These results suggest arelative net cooling occurring between late Cretaceous and early Paleogene of ArgentinePatagonia.