Late Paleocene fossils from the Cerrejón Formation, Colombia, are the earliest record of Neotropical rainforest

Abstract

Neotropical rainforests have a very poor fossil record, making hypotheses concerning their origins difficult to evaluate. Nevertheless, some of their most important characteristics can be preserved in the fossil record: high plant diversity, dominance by a distinctive combination of angiosperm families, a preponderance of plant species with large, smooth-margined leaves, and evidence for a high diversity of herbivorous insects. Here, we report on an Ϸ58-my-old flora from the Cerrejó n Formation of Colombia (paleolatitude Ϸ5°N) that is the earliest megafossil record of Neotropical rainforest. The flora has abundant, diverse palms and legumes and similar family composition to extant Neotropical rainforest. Three-quarters of the leaf types are large and entiremargined, indicating rainfall >2,500 mm/year and mean annual temperature >25°C. Despite modern family composition and tropical paleoclimate, the diversity of fossil pollen and leaf samples is 60 -80% that of comparable samples from extant and Quaternary Neotropical rainforest from similar climates. Insect feeding damage on Cerrejó n fossil leaves, representing primary consumers, is abundant, but also of low diversity, and overwhelmingly made by generalist feeders rather than specialized herbivores. Cerrejó n megafossils provide strong evidence that the same Neotropical rainforest families have characterized the biome since the Paleocene, maintaining their importance through climatic phases warmer and cooler than present. The low diversity of both plants and herbivorous insects in this Paleocene Neotropical rainforest may reflect an early stage in the diversification of the lineages that inhabit this biome, and/or a long recovery period from the terminal Cretaceous extinction. diversity ͉ stability ͉ paleoclimate ͉ paleobotany ͉ Fabaceae

Angiosperms Helped Put the Rain in the Rainforests: The Impact of Plant Physiological Evolution on Tropical Biodiversity1

“…Evidence for megathermal angiosperm rainforests in the Paleocene is unambiguous at both tropical and temperate latitudes (Johnson & Ellis, 2002;Wing et al, 2009), but Cretaceous evidence is mixed. This problem persists, in part, because macrofossil records are extremely scarce in the modern tropics (Burnham & Johnson, 2004;Wing et al, 2009). Furthermore, interpretation can be ambiguous for the more frequently available evidence from microfossils, climate-sensitive sediments, geochemistry, climate modeling, and inference from living plants.…”

“…However, climate-sensitive sediments and modeling support at least local persistence of environmental conditions compatible with growth of megathermal rainforests at tropical and/or temperate latitudes during the Cretaceous (Parrish et al, 1982;Barron & Washington, 1985;Parrish, 1987;Upchurch et al, 1999;Beerling & Woodward, 2001;Ziegler et al, 2003;Ufnar et al, 2008). Nonetheless, most paleobotanical macrofossil studies suggest that the establishment of angiosperm rainforests was delayed until the early Tertiary, based on the paucity of wood indicative of large angiosperm trees or of large seeds suggestive of closed-canopy environments in the Cretaceous (Tiffney, 1984;Wheeler & Baas, 1991;Wing & Boucher, 1998). This paleobotanical evidence is complicated by the leaf physiognomies of individual temperate-latitude localities suggesting warm, wet forests as early as the Cenomanian about 100 million years ago (Upchurch & Wolfe, 1987) and by recent arguments that large seed size is an advantage for germination in deep shade rather than a requirement (reviewed in Feild et al, 2004;Davis et al, 2005).…”

“…However, the exact timing of the origin of angiosperm-dominated tropical rainforests of modern aspect is debated (Upchurch & Wolfe, 1987;Morley, 2000;Burnham & Johnson, 2004;Davis et al, 2005;Wing et al, 2009). Evidence for megathermal angiosperm rainforests in the Paleocene is unambiguous at both tropical and temperate latitudes (Johnson & Ellis, 2002;Wing et al, 2009), but Cretaceous evidence is mixed. This problem persists, in part, because macrofossil records are extremely scarce in the modern tropics (Burnham & Johnson, 2004;Wing et al, 2009).…”

Biogeographic and evolutionary implications of a diverse paleobiota in amber from the early Eocene of India

“…Molecular estimates of the origins of broad-leaved (angiospermous) tropical forests range from the Early to mid-Cretaceous (53), which conflicts with direct macrofossil evidence such as leaves and wood, that such forests developed in the early Cenozoic, generally the Eocene to Paleocene (54)(55)(56)(57)(58), with the earliest records being the Early to Late Paleocene of the Western Hemisphere (55,58). One reason for the discrepancy is that molecular estimates are typically much older than divergence times based on morphology and fossils (59,60).…”

Early Paleocene landbird supports rapid phylogenetic and morphological diversification of crown birds after the K–Pg mass extinction

“…In North America, mammalian diversity levels began to surpass the benchmarks observed in the latest Cretaceous just a few million years after the extinction (1,2). The placental mammal radiation is thought to be part of a broader diversification that occurred on a recovering terrestrial landscape dominated by flowering plants (angiosperms) (3,4).…”