title: A critical transition in leaf evolution facilitated the Cretaceous angiosperm revolution.
abstract: The revolutionary rise of broad-leaved (flowering) angiosperm plant species during the Cretaceous initiated a global ecological transformation towards modern biodiversity. Still, the mechanisms involved in this angiosperm radiation remain enigmatic. Here we show that the period of rapid angiosperm evolution initiated after the leaf interior (post venous) transport path length for water was reduced beyond the leaf interior transport path length for CO2 at a critical leaf vein density of 2.5-5 mm mm(-2). Data and our modelling approaches indicate that surpassing this critical vein density was a pivotal moment in leaf evolution that enabled evolving angiosperms to profit from developing leaves with more and smaller stomata in terms of higher carbon returns from equal water loss. Surpassing the critical vein density may therefore have facilitated evolving angiosperms to develop leaves with higher gas exchange capacities required to adapt to the Cretaceous CO2 decline and outcompete previously dominant coniferous species in the upper canopy.
authors.affiliation: Department of Environmental Sciences, Faculty of Geosciences, Utrecht University, Heidelberglaan 2, PO box 80115, Utrecht 3508 TC, The Netherlands. h.j.deboer@uu.nl
authors.forename: Hugo Jan
authors.initials: HJ
authors.lastname: de Boer
authors.forename: Maarten B
authors.initials: MB
authors.lastname: Eppinga
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Wassen
authors.forename: Stefan C
authors.initials: SC
authors.lastname: Dekker
mesh_terms: D005075:Biological Evolution; D002245:Carbon Dioxide / Q000378:metabolism; D019684:Magnoliopsida / Q000033:anatomy & histology* / Q000502:physiology; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000502:physiology; D054046:Plant Stomata / Q000033:anatomy & histology / Q000502:physiology; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water; D002245:Carbon Dioxide