rspb.royalsocietypublishing.org Research Cite this article: Friis EM, Pedersen KR, Crane PR. 2016 The emergence of core eudicots: new floral evidence from the earliest Late Cretaceous. Proc. R. Soc. B 283: 20161325. http://dx.doi.org/10.1098/rspb.2016.1325 Received: 11 June 2016 Accepted: 14 November 2016 Subject Areas: evolution, palaeontology, structural biology Keywords: fossil flower, rosids, asterid, SRXTM, synchrotron X-ray microtomography, tricolporate pollen Author for correspondence: Else Marie Friis e-mail: else.marie.friis@nrm.se Electronic supplementary material is available online at https://dx.doi.org/10.6084/m9.fig- share.c.3588719. The emergence of core eudicots: new floral evidence from the earliest Late Cretaceous Else Marie Friis 1 , Kaj Raunsgaard Pedersen 2 and Peter R. Crane 3,4 1 Department of Palaeobiology, Swedish Museum of Natural History, Stockholm, Sweden 2 Department of Geoscience, University of Aarhus, Aarhus, Denmark 3 Yale School of Forestry and Environmental Studies, New Haven, CT, USA 4 Oak Spring Garden Foundation, Upperville, VA, USA EMF, 0000-0003-2936-2761 Eudicots, the most diverse of the three major clades of living angiosperms, are first recognized in the latest Barremian–earliest Aptian. All Early Cretaceous forms appear to be related to species-poor lineages that diverged before the rise of core eudicots, which today comprise more than 70% of angiosperm species. Here, we report the discovery of a well-preserved flower, Caliciflora mauldinensis, from the earliest Late Cretaceous, with unequivocal core eudicot features, including five sepals, five petals and two whorls of stamens borne on the rim of a floral cup containing three free carpels. Pollen is tricolporate. Carpels mature into follicular fruitlets. This character combination suggests a phylogenetic position among rosids, but more specific assignment is precluded by complex patterns of character evolution among the very large number of potentially relevant extant taxa. The whorled floral organization is consistent with ideas that this stable pattern evolved early and was a pre- requisite for more integrated patterns of floral architecture that evolved later. However, limited floral synorganization in Caliciflora and all earlier eudicot flowers recognized so far, calls into question hypotheses that substan- tial diversification of core eudicots had already occurred by the end of the Early Cretaceous. 1. Introduction Hypotheses of relationships among living angiosperms recognize a species-poor basal grade, within which are embedded three major clades; eumagnoliids, mono- cots and eudicots. Soon after their first appearance in the fossil record about 135 Ma, Early Cretaceous angiosperms include diverse extinct taxa related to basal grade angiosperms (Austrobaileyales, Chloranthaceae and Nymphaeales), certain eumagnoliids (Laurales, Magnoliales and Piperales), early monocots (Alismatales) and basal grade eudicots (e.g. [1–4]). These Early Cretaceous assem- blages contrast markedly with Late Cretaceous angiosperm assemblages that are dominated by fossils related to lineages of core eudicots. Core eudicots comprise more than 70% of living angiosperm species and both major clades within the group are well represented in the Late Cretaceous. Late Cretaceous rosids include a rich record of early Fagales (e.g. [5]) as well as diverse fossils related to other clades [1]. Late Cretaceous asterids include many taxa related to extant Cornales and Ericales (e.g. [1,6–9]), the two earliest diverging lineages of the group. The transition from Early Cretaceous floras, dominated by basal grade lineages of angiosperms, eumagnoliids and early eudicots, to Late Cretaceous floras dominated by core eudicots, occurred sometime between the mid-Albian and the Turonian–Santonian. Here, we describe a new flower from the earliest Late Cretaceous (earliest Cenomanian) of eastern North America with distinctive fea- tures of core eudicots. Together with an unnamed fossil flower of approximately & 2016 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.