How deep is the conflict between molecular and fossil evidence on the age of angiosperms?

Abstract

Summary The timing of the origin of angiosperms is a hotly debated topic in plant evolution. Molecular dating analyses that consistently retrieve pre‐Cretaceous ages for crown‐group angiosperms have eroded confidence in the fossil record, which indicates a radiation and possibly also origin in the Early Cretaceous. Here, we evaluate paleobotanical evidence on the age of the angiosperms, showing how fossils provide crucial data for clarifying the situation. Pollen floras document a Northern Gondwanan appearance of monosulcate angiosperms in the Valanginian and subsequent poleward spread of monosulcates and tricolpate eudicots, accelerating in the Albian. The sequence of pollen types agrees with molecular phylogenetic inferences on the course of pollen evolution, but it conflicts strongly with Triassic and early Jurassic molecular ages, and the discrepancy is difficult to explain by geographic or taphonomic biases. Critical scrutiny shows that supposed pre‐Cretaceous angiosperms either represent other plant groups or lack features that might confidently assign them to the angiosperms. However, the record may allow the Late Jurassic existence of ecologically restricted angiosperms, like those seen in the basal ANITA grade. Finally, we examine recently recognized biases in molecular dating and argue that a thoughtful integration of fossil and molecular evidence could help resolve these conflicts.

The dynamics of stem and crown groups

“…1b) can be seen to be unlikely under the model; rather, the reverse is always true. This is particularly important in clades where molecular clocks suggest a deep origin of the crown group during an interval of time when the stem group is seen to be diversifying in the fossil record, with classic examples being animals, angiosperms, birds and mammals [27,9,28,18,11] (Fig. 1b).…”

Nuclear phylogenomic analyses of asterids conflict with plastome trees and support novel relationships among major lineages

“…We used treePL to date the plastome phylogeny and each individual gene tree, and for each we ran cross‐validation tests prior to the final analysis to determine the optimal smoothing parameters (see configuration files for more details, available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.h70rxwdfq [Stull et al., ]). Given the difficulty of consistently calibrating individual gene trees with differences in both relationships and included species, we employed only two calibrations: (1) one for crown eudicots, with the minimum age set at 125.0 Ma (corresponding to the first appearance of tricolpate pollen; Doyle et al., ; Hughes and McDougall, ) and the maximum age set at 135.0 Ma (corresponding approximately to the oldest reliable fossil evidence of angiosperms; Trevisan, ; Brenner, ; Friis et al., ; Coiro et al., ); and (2) another for crown Asteridae , with the minimum age set at 115.75 Ma (based on the penalized likelihood minimum estimate from 100 ML bootstrap trees in Magallón et al., ) and the maximum age set at 125.0 Ma (the first fossil appearance of eudicots, the broader clade including Asteridae ). This more minimal calibration scheme allowed us to consistently calibrate nearly all gene trees, while weighting the significance of the eudicot calibration, which is generally considered one of the better angiosperm calibration points in that it likely captures eudicots relatively close to their actual geologic origin (Friis et al., ).…”

Darwin review: angiosperm phylogeny and evolutionary radiations

“…The possibility of an earlier origin of 'ecologically restricted angiosperms', perhaps in the Jurassic, may be consistent with both molecular and fossil evidence (cf. [7]). Friedman [6, p. 5] interprets, however, that the most abominable issue for Darwin was not that the evolutionary origins of angiosperms were unclear but that '.…”