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The photosynthetic gas exchange capacities of early angiosperms remain enigmatic. Nevertheless, many hypotheses about the causes of early angiosperm success and how angiosperms influenced Mesozoic ecosystem function hinge on understanding the maximum capacity for early angiosperm metabolism. We applied structure-functional analyses of leaf veins and stomatal pore geometry to determine the hydraulic and diffusive gas exchange capacities of Early Cretaceous fossil leaves. All of the late Aptian–early Albian angiosperms measured possessed low vein density and low maximal stomatal pore area, indicating low leaf gas exchange capacities in comparison to modern ecologically dominant angiosperms. Gas exchange capacities for Early Cretaceous angiosperms were equivalent or lower than ferns and gymnosperms. Fossil leaf taxa from Aptian to Paleocene sediments previously identified as putative stem-lineages to Austrobaileyales and Chloranthales had the same gas exchange capacities and possibly leaf water relations of their living relatives. Our results provide fossil evidence for the hypothesis that high leaf gas exchange capacity is a derived feature of later angiosperm evolution. In addition, the leaf gas exchange functions of austrobaileyoid and chloranthoid fossils support the hypothesis that comparative research on the biology of living basal angiosperm lineages reveals genuine signals of Early Cretaceous angiosperm ecophysiology.

Item Type:	Refereed Article
Research Division:	Biological Sciences
Research Group:	Evolutionary Biology
Research Field:	Biological Adaptation
Objective Division:	Environment
Objective Group:	Flora, Fauna and Biodiversity
Objective Field:	Forest and Woodlands Flora, Fauna and Biodiversity
Author:	Brodribb, TJ (Professor Tim Brodribb)
ID Code:	71960
Year Published:	2011
Web of Science® Times Cited:	28
Deposited By:	Plant Science
Deposited On:	2011-08-16
Last Modified:	2017-10-24
Downloads:	2 View Download Statistics