Research Constraining uncertainty in the timescale of angiosperm evolution and the veracity of a Cretaceous Terrestrial Revolution Jose Barba-Montoya1 , Mario dos Reis2 , Harald Schneider3,4, Philip C. J. Donoghue5 and Ziheng Yang1 1Department of Genetics, Evolution and Environment, University College London, Darwin Building, Gower Street, London, WC1E 6BT, UK; 2School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London, E1 4NS, UK; 3Center of Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Yunnan, China; 4Department of Botany, Natural History Museum, Cromwell Road, London, SW7 5BD, UK; 5School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol, BS8 1TQ, UK Summary Authors for correspondence: Through the lens of the fossil record, angiosperm diversification precipitated a Cretaceous Ziheng Yang Terrestrial Revolution (KTR) in which pollinators, herbivores and predators underwent explo- Tel: +44 020 7679 2000, ext. 34379 sive co-diversification. Molecular dating studies imply that early angiosperm evolution is not Email: [email protected] documented in the fossil record. This mismatch remains controversial. Philip C. J. Donoghue We used a Bayesian molecular dating method to analyse a dataset of 83 genes from 644 Tel: +44 011 7394 1209 taxa and 52 fossil calibrations to explore the effect of different interpretations of the fossil Email: [email protected] record, molecular clock models, data partitioning, among other factors, on angiosperm diver- Received: 6 June 2017 gence time estimation. Accepted: 20 December 2017 Controlling for different sources of uncertainty indicates that the timescale of angiosperm diversification is much less certain than previous molecular dating studies have suggested. Dis- New Phytologist (2018) 218: 819–834 cord between molecular clock and purely fossil-based interpretations of angiosperm diversifi- doi: 10.1111/nph.15011 cation may be a consequence of false precision on both sides. We reject a post-Jurassic origin of angiosperms, supporting the notion of a cryptic early his- tory of angiosperms, but this history may be as much as 121 Myr, or as little as 23 Myr. These Key words: angiosperms, Bayesian analysis, conclusions remain compatible with palaeobotanical evidence and a more general KTR in Cretaceous Terrestrial Revolution, divergence time, fossil record. which major groups of angiosperms diverged later within the Cretaceous, alongside the diver- sification of pollinators, herbivores and their predators. et al., 2011; Magallon et al., 2015; Herendeen et al., 2017). Some Introduction interpret this evidence literally to reflect an explosive radiation Angiosperms constitute one of the largest scions of the tree of life. from a Cretaceous crown-ancestor, with the earliest macrofossil They dominate extant plant diversity, occupy almost every habi- record of unambiguous crown-angiosperms (Friis et al., 2000; tat on Earth and are one of the principal components of modern Sun et al., 2002) dating back only to the mid-Early Cretaceous biota playing crucial roles in terrestrial ecosystems (Augusto et al., (Hickey & Doyle, 1977; Benton, 2010; Friis et al., 2010; Mered- 2014; Cascales-Minana~ et al., 2016). Angiosperms rose to ecolog- ith et al., 2011; Doyle, 2012; Gomez et al., 2015; Cascales- ical dominance in the Cretaceous Terrestrial Revolution (KTR), Minana~ et al., 2016; Herendeen et al., 2017). In stark contrast, when their apparently explosive radiation is believed to have molecular timescales for angiosperm evolution have invariably underpinned the diversification of lineages that are key compo- concluded that crown-angiosperms diverged as much as 100 mil- nents of contemporary terrestrial environments, such as birds, lion yr (Myr) earlier than the KTR (e.g. Bell et al., 2005, 2010; insects, mammals and seed-free land plants, foreshadowing mod- Magallon, 2010, 2014; Smith et al., 2010; Clarke et al., 2011; ern terrestrial biodiversity (Dilcher, 2000; Benton, 2010; Mered- Magallon et al., 2013; Zanne et al., 2014; Zeng et al., 2014; ith et al., 2011; Cardinal & Danforth, 2013; Augusto et al., Beaulieu et al., 2015; Foster et al., 2016; Murat et al., 2017) – 2014; Cascales-Minana~ et al., 2016). However, these hypotheses unless they have been forced to fit with the early fossil record of co-diversification rest largely on the perceived coincidence in angiosperms (Magallon & Castillo, 2009; Magallon et al., 2015) the radiation of angiosperms and the renewal of trophic networks – (Table 1), implying a long cryptic evolutionary history unrepre- in terrestrial ecosystems. This is evidenced, not least, by the fossil sented in the fossil record. This may be because early angiosperms record of tricolpate pollen in the Barremian, slightly younger were not ecologically significant, or were living in environments Aptian floral assemblages, followed by an explosive increase in in which fossilization was unlikely (Raven & Axelrod, 1974; diversity in the middle and late Cretaceous (Doyle, 2008; Clarke Feild et al., 2009; Friedman, 2009; Smith et al., 2010; Doyle, Ó 2018 The Authors New Phytologist (2018) 218: 819–834 819 New Phytologist Ó 2018 New Phytologist Trust www.newphytologist.com This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 820 Research New Phytologist www.newphytologist.com Table 1 Overview of estimates of divergence times for selected major groups of angiosperms for some selected analyses from previous studies (2018) Clade (crown group) 218: Study Data/analysis Angiosperms Magnoliids Monocots Eudicots Superrosids Rosids Superasterids Asterids 819–834 Bell et al. (2005) Loci: 2-plastid, 1-mt, 1-nuc. 140–180 Ma – 99–133 Ma 93–125 Ma ––– – Taxa: 71. Calib: 5./BRC Loci: 2-plastid, 1-mt, 1-nuc. 155–198 Ma – 123–126 Ma –––– – Taxa: 71. Calib: 5./PL Magallon & Castillo (2009) Loci: 3-plastid. Taxa: 256. 130–242 Ma –––––– – Calib: 13./PL Bell et al. (2010) Loci: 2-plastid, 1-nuc. 141–154 Ma 121–130 Ma – 123–134 Ma 111–121 Ma 97–105 Ma 113–132 Ma 98–111 Ma Taxa: 567. Calib: 36a./IR Loci: 2-plastid, 1-nuc. 167–199 Ma 108–138 Ma – 123–139 Ma 111–135 Ma 97–132 Ma 113–131 Ma 98–119 Ma Taxa: 567. Calib: 36b./IR Smith et al. (2010) Loci: 2-plastid, 1-nuc. 182–257 Ma 136–181 Ma 139–167 Ma 128–147 Ma ––– – Taxa: 154. Calib: 33./IR Loci: 2-plastid, 1-nuc. 193–270 Ma 138–198 Ma 141–191 Ma 138–172 Ma ––– – Taxa: 154. Calib: 32./IR Clarke et al. (2011) Loci: 7-plastid. Taxa: 18. 175–240 Ma ––83–115 Ma ––– – Calib: 17./IR Magallon et al. (2013) Loci: 5-plastid. Taxa: 80. 162–210 Ma 131–155 Ma 125–145 Ma 120–129 Ma ––– – Calib: 28./IR Magallon (2014) Loci: 5-plastid. Taxa: 81. 162–210 Ma –––––– – Calib: 27./IR Zanne et al. (2014) Loci: 11-plastid, 4-mt, 243 Ma 147 Ma 171 Ma 137 Ma 118 Ma 117 Ma 117 Ma 108 Ma 2-nuc. Taxa: 32 223. Calib: 39./PL Zeng et al. (2014) Loci: 59-nuc. Taxa: 61. 286–246 Ma 122–150 Ma 127–149 Ma 115–126 Ma ––– – Calib: 2./IR Magallon et al. (2015) Loci: 3-plastid, 2-nuc. 139.4 Ma 130–134 Ma 132–135 Ma 130–133 Ma 119–125 Ma 115–123 Ma 120–126 Ma 110–119 Ma Taxa: 798. Calib: 137./IR Beaulieu et al. (2015) Loci: 3-plastid, 1-nuc. 210–253 Ma 160–195 Ma 149–181 Ma 142–170 Ma 124–144 Ma 113–136 Ma 120–143 Ma 99–119 Ma New Phytologist Taxa: 125. Calib: 24./IR Foster et al. (2016) Loci: 76-plastid. Taxa: 192–251 Ma 130–171 Ma 141–176 Ma 136–154 Ma 123–135 Ma 118–131 Ma 107–126 Ma 108–124 Ma 195. Calib: 37./IR Murat et al. (2017) Loci: 1175. Taxa: 37. 190–238 Ma ––87–109 Ma ––– – Calib: 2./IR Ó – – – – – – – – 2018 New Phytologist Trust This study (composite) Loci: 77-plastid, 4-mt, 149 256 Ma 128 190 Ma 123 181 Ma 129 188 Ma 118 162 Ma 117 160 Ma 118 164 Ma 107 146 Ma 2-nuc. Taxa: 644. Calib: 52./IR Ó BRC, Bayesian relaxed clock (Multidivetime); PL, penalized likelihood; AR, autocorrelated rates model; IR, independent rates model; SC, strict clock model; Calib, calibration points; composite, 95% 2018 The Authors high posterior density credibility interval (HPD CI) is a composite of the 95% HPD credibility intervals across all calibration strategies, except calibration strategy B (SB). Ma, million years ago. See Phytologist New original works for further information on time estimates. New Phytologist Research 821 2012). Or it may be that molecular clock estimates are just unre- combined the molecular data and fossil calibrations in a Bayesian alistically old, perhaps an artefact of their failure to accommodate relaxed clock divergence time analysis. The Bayesian approach dramatic accelerations that may have been associated with an used here (Rannala & Yang, 2007; dos Reis & Yang, 2011) inte- explosive diversification of angiosperms (Magallon, 2010; grates over the uncertainty in rate variation along the phylogeny. Beaulieu et al., 2015; Brown & Smith, 2017). We explored the impact of different sources of uncertainty on the Moreover, the timescale of angiosperm diversification varies timescale of angiosperm diversification. We employed five cali- broadly amongst different molecular analyses (Table 1). This is bration strategies that accommodate different interpretations of not surprising given that the transformation of molecular dis- the fossil record, and showed that these have a strong impact on tances (the branch lengths on a phylogeny) into geological diver- posterior estimates. We also explored the impact of data parti- gence times is challenging (dos Reis & Yang, 2013). Certainly, tioning, parameter choice in priors for rates and times, relaxed there are a number of methodological variables in previous molecular clocks and the effect of outgroup sampling.