Angiosperm leaves and cuticles from the uppermost Cretaceous of Patagonia, biogeographic implications and atmospheric paleo-CO2 estimates

Abstract

The study of plant material from localities of Late Cretaceous age from southern latitudes is fundamental to improve our understanding of global patterns of angiosperm evolution, diversity, paleoecology, and biogeography. Herein, angiosperm leaf fossils of the recently discovered Cañadón del Loro locality, from the Maastrichtian portion of the Lefipán Formation, Patagonia, Argentina are studied. Leaf architecture was used to differentiate morphotypes, to describe them, and to make comparisons with other southern latitudes floras of similar age. Six angiosperm leaf morphotypes were described from 132 collected specimens; one of them, with exceptional preservation, was named Lefipania padillae gen. et sp. nov. and its cuticle anatomy and insect damage were also described. The Cañadón del Loro fossils represent a local assemblage of low diversity deposited in an upper delta plain. Biogeographically, L. padillae was widespread throughout the southern hemisphere during the Late Cretaceous, possibly favored by a warm climate and the geographical proximity of these southern landmasses. The morphotype with well-preserved cuticles clearly shows four insect damage types attributed to feeding. This morphotype was also used for estimating paleo-atmospheric CO2 concentration (pCO2), using a stomatal-proxy gas exchange model, which resulted in approximately 464 ppm. The estimated pCO2 is in agreement with previous estimations for this time interval and supports the hypothesis of a decrease of pCO2 towards end of the Cretaceous.