title: Exceptional preservation of tiny embryos documents seed dormancy in early angiosperms.
abstract: The rapid diversification of angiosperms through the Early Cretaceous period, between about 130-100 million years ago, initiated fundamental changes in the composition of terrestrial vegetation and is increasingly well understood on the basis of a wealth of palaeobotanical discoveries over the past four decades and their integration with improved knowledge of living angiosperms. Prevailing hypotheses, based on evidence both from living and from fossil plants, emphasize that the earliest angiosperms were plants of small stature with rapid life cycles that exploited disturbed habitats in open, or perhaps understorey, conditions. However, direct palaeontogical data relevant to understanding the seed biology and germination ecology of Early Cretaceous angiosperms are sparse. Here we report the discovery of embryos and their associated nutrient storage tissues in exceptionally well-preserved angiosperm seeds from the Early Cretaceous. Synchrotron radiation X-ray tomographic microscopy of the fossil embryos from many taxa reveals that all were tiny at the time of dispersal. These results support hypotheses based on extant plants that tiny embryos and seed dormancy are basic for angiosperms as a whole. The minute size of the fossil embryos, and the modest nutrient storage tissues dictated by the overall small seed size, is also consistent with the interpretation that many early angiosperms were opportunistic, early successional colonizers of disturbance-prone habitats.
authors.affiliation: Department of Palaeobiology, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden.|Yale School of Forestry and Environmental Studies, 195 Prospect Street, New Haven, Connecticut 06511, USA.
authors.forename: Else Marie
authors.initials: EM
authors.lastname: Friis
authors.affiliation: Yale School of Forestry and Environmental Studies, 195 Prospect Street, New Haven, Connecticut 06511, USA.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Crane
authors.affiliation: Yale School of Forestry and Environmental Studies, 195 Prospect Street, New Haven, Connecticut 06511, USA.|Department of Earth Science, University of Aarhus, DK-8000 Aarhus, Denmark.
authors.forename: Kaj Raunsgaard
authors.initials: KR
authors.lastname: Pedersen
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.|Institute for Biomedical Engineering, ETZ F 85, Swiss Federal Institute of Technology Zurich, Gloriastrasse 35, CH-8092 Zurich, Switzerland.
authors.forename: Marco
authors.initials: M
authors.lastname: Stampanoni
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.
authors.forename: Federica
authors.initials: F
authors.lastname: Marone
mesh_terms: D049628:Body Size; D018548:Cotyledon / Q000033:anatomy & histology / Q000196:embryology; D005580:Fossils; D018525:Germination; D019684:Magnoliopsida / Q000033:anatomy & histology* / Q000166:cytology / Q000196:embryology*; D008853:Microscopy; D057445:Plant Dormancy; D012639:Seeds / Q000033:anatomy & histology* / Q000166:cytology / Q000196:embryology*; D017356:Synchrotrons; D014056:Tomography, X-Ray