Original paper
Conifer turnover across the K/Pg boundary in Colorado, U.S.A., parallels South American patterns: New and emerging perspectives
Berry, Keith
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen Band 303 Heft 1 (2022), p. 11 - 28
146 references
published: Jan 28, 2022
manuscript accepted: Nov 22, 2021
manuscript received: Oct 4, 2021
ArtNo. ESP155030301001, Price: 29.00 €
Abstract
There is no consensus on the cause of decline in conifer diversity across the K/Pg boundary, particularly in relation to the evolution and modernization of the tropical rainforest biome and the global rise of angiosperm diversity. In order to elucidate this issue, the pattern of conifer turnover across the K/Pg boundary in the Raton and Denver basins is revisited in light of additional fieldwork and improved chronostratigraphy. Turnover between the late Maastrichtian tropical evergreen climax conifer assemblage and the early Paleocene pioneer swamp cypress assemblage was stratigraphically abrupt, occurring within ±1–2 m of the K/Pg boundary. As the swamp cypress Glyptostrobus is known to be intolerant of competition, its persistence through the P1 Zone (lowest Danian palynological zone, which represents the first ~400 ky of the Danian) in relatively stable, peat-forming depositional settings in Colorado is interpreted as evidence of arrested succession associated with the extinction of the tropical evergreen climax community. Although this basic pattern has historically been attributed to selection for deciduousness across the K/Pg boundary, this investigation highlights the related fact that tropical evergreen araucarian conifers and other trees in tropical evergreen climax forests characteristically do not produce soil seed banks, particularly as the archaic climax conifers that not only crossed the boundary but which also thrived in tropical, drought-prone settings are known to exhibit seed dormancy (e.g., Cheirolepidiaceae). As these findings parallel those of recent paleobotanical investigations in South America (Colombia and Patagonia, Argentina), this fundamental turnover pattern is regarded to be a global phenomenon underpinned by a unifying causal factor – that is, a relatively severe K/Pg asteroid impact winter with global effects. Other popular but more controversial turnover hypotheses, such as the concept that conifers and other gymnosperms exhibit lower propensity for polyploidization-driven diversification than angiosperms, are also critically reconsidered in light of new and emerging evidence.
Keywords
K/Pg boundary • mass extinction • conifers • arrested succession • seed dormancy