Fossil pollen records reveal a late rise of open-habitat ecosystems in Patagonia

Abstract

The timing of major turnovers in terrestrial ecosystems of the Cenozoic Era has been largely interpreted from the analysis of the assumed feeding preference of extinct mammals. For example, the expansion of open-habitat ecosystems (grasslands or savannas) is inferred to have occurred earlier in Patagonia than elsewhere because of the early advent of highcrowned teeth (hypsodont) mammals B26 Ma ago. However, the plant fossil record from Patagonia implies another evolutionary scenario. Here we show that the dominance of key open-habitat species-amaranths, Ephedra, asters and grasses-occurred during the last 10 Ma, about 15 Ma later than previously inferred using feeding/habitat ecology of extinct mammals. This late rise of open-landscapes in southern South America brings into question whether the expansion of open-habitat vegetation could have been the prime factor of highcrowned mammal diversification.

Fossil pollen records indicate that Patagonian desertification was not solely a consequence of Andean uplift

“…As this inland sea contracted during the Late Miocene, it would have left the Patagonian interior more arid and would also have intensified the continentality, with warmer summers and colder winters. The expansion of open-habitat plant lineages by the late Miocene is also consistent with this change in land-sea distribution 24 . Pliocene terrestrial deposits (Río Negro Fm.)…”

Ontogenetic and life history trait changes associated with convergent ecological specializations in extinct ungulate mammals

“…Among factors leading to dietary changes, increasing aridity could have at least triggered the emergence and abundance of new types of vegetation, such as shrublands observed in Patagonia during the second part of the Paleogene (16,29) (Fig. 3C), although forests probably remained dominant until the Middle Miocene in South America (15,39), especially in the northern part (14). Pending more precise environmental data, it seems at least reasonable to assume that the acquisition of a more durable and rapidly efficient dentition allowed notoungulates to widen the spectrum of plants consumed (19,40,41) in being more tolerant toward abrasives, which partly led to their subsequent specializations.…”

Quasi-static Eocene–Oligocene climate in Patagonia promotes slow faunal evolution and mid-Cenozoic global cooling

“…These data conclusively rule out the occurrence of grasslands through the sequence analyzed. However, although phytolith and sparse pollen data were originally interpreted as indicating relatively closed, forested habitats (Palazzesi and Barreda, 2012;Strömberg et al, 2013), new research on phytolith micromorphology implies that Patagonian plant communities experienced high light levels…”

“…Most spectacularly, South American notoungulates and other herbivorous lineages show a pattern of increasing cheek tooth crown height starting the middle Eocene (~38 Ma), classically hypothesized to reflect an evolutionary response to linked climate and vegetation change during the Eocene-Miocene (e.g., Stebbins, 1981;Jacobs et al, 1999;Madden et al, 2010;Strömberg, 2011). Many studies have attempted to test this hypothesis by reconstructing vegetation structure and composition through paleobotanical evidence or indirect proxies (e.g., Croft, 2001;Palazzesi and Barreda, 2012;Strömberg et al, 2013;Dunn et al, 2015). However, most do not explicitly link vegetation and faunal data to regional and global climate reconstructions to investigate the interplay among global climate change, ocean circulation and local climates and ecologies.…”