LETTER LETTER

Phylogenetic uncertainty and fossil calibration of chronograms

Barreda et al. (1) claim a Cretaceous fossil by few characters. Crucial character scoring and calibration. Ages for these type is an extinct Asteraceae. Con- encoding are particularly difficult from taxa of divergences result chiefly from the place- cluding this pollen type is “nested within the dispersed pollen fossil record (2). Extant ment here of the Mutisiapollis telleriae + (crown representative),” they Dasyphyllum, ,andDoniophyton Raiguenrayun constraint as rationalized by calibrate a Dasyphyllum + Barnadesia crown have an exine bilayer (3), but when the Panero et al. (4), not at the Asteraceae crown node node (Dasyphyllum crown absent) and esti- same character observed under light micros- shown by Barreda et al. (5). These two calibrations mate an 85.9-Ma Asteraceae crown age that copy is scored (character 21), Dasyphyllum placed in Asteraceae result in contrasting potentially compresses asterid evolution by spp. share a single layer state with the fossil early evolutionary patterns in tens of millions of years. However, the boot- as opposed to other Barnadesioideae. Encod- vs. the sister clade (stem lengths in figure 5 in strap majority consensus topology reported ing “columellate layer visibility under light ref. 1). The authors do not comment on this could not be reproduced from the data; in- microscopy” (character 19) results in unin- interesting consequence of their calibration stead, the fossil resolved in a trichotomy tentional character weighting. Exine thickness placement, an effect that shrinks when the with and Asteraceae. Thus, un- (character 22) is much smaller in Dasyphyllum T. lilliei type A calibration is placed outside ambiguous assignment of these pollen grains inerme and Dasyphyllum velutinum than in Asteraceae (figure S5 in ref. 1). to Asteraceae is premature. other Dasyphyllum spp. (3) that would be 1 Paleocene, not Cretaceous, mean ages of scored as other Barnadesioideae and differ- Jose L. Panero Asteraceae result from calibration placement ent from the fossil had they been sampled. Department of Integrative Biology, The consistent with the fossil’sphylogeneticposi- Characters 19, 21, and 22 clearly contribute University of Texas, Austin, TX 78712 tion in the reproduced bootstrap . Cali- to place the fossil with Dasyphyllum.Character bration at the Asteraceae + Calyceraceae 17 assumes that concavities distributed asym- crown node (second calibration scenario; metrically (sometimes absent) along the inter- 1 Barreda VD, et al. (2015) Early evolution of the angiosperm clade figure S5A and table S2 of ref. 1) is not con- colpal region in the fossil are homologous Asteraceae in the Cretaceous of Antarctica. Proc Natl Acad Sci USA 112(35):10989–10994. sistent with the bootstrap, because it excludes with symmetrically distributed intercolpal 2 Crepet WL, Nixon KC, Gandolfo MA (2004) Fossil evidence and the possibility that the fossil is a stem mem- concavities in extant taxa and not the result phylogeny: The age of major angiospermcladesbasedonmesofossiland ber of the Asteraceae + Calyceraceae clade. of compression forces during fossilization macrofossil evidence from Cretaceous deposits. Am J Bot 91(10):1666–1682. 3 Tellería MC, Palazzesi L, Barreda VC (2015) Evolutionary significance The third scenario placement is consistent (figure 4 in ref. 1). This character is scored of exine ultrastructure in the subfamily Barnadesioideae (Asteraceae) in with the fossil + Asteraceae + Calyceraceae as “present” in the fossil (table S1 in ref. 1) the light of molecular phylogenetics. Rev Palaeobot Palynol 221:32–46. “ ” 4 Panero JL, et al. (2014) Resolution of deep nodes yields an trichotomy supported by 69% bootstrap pro- but described as present or absent [sup- improved backbone phylogeny and a new basal lineage to study early portion. The study’s six calibration scenarios porting information (p. 2) in ref. 1]. The evolution of Asteraceae. Mol Phylogenet Evol 80:43–53. illustrate the ambiguous phylogenetic posi- authors did not explore the robustness of 5 Barreda VD, et al. (2012) An extinct Eocene taxon of the daisy family (Asteraceae): Evolutionary, ecological and biogeographical tion (identity) of Tubulifloridites lilliei type phylogenetic results to alternative scoring, implications. Ann Bot (Lond) 109(1):127–134. A pollen that hinders unequivocal placement encoding, or Dasyphyllum sampling. in chronogram construction. Readers should not construe finding Furthermore, we should be cautious of Paleocene-Eocene hothouse climate coincident Author contributions: J.L.P. wrote the paper. sensational conclusions underpinned by an with diversification of South American line- The author declares no conflict of interest. inferred phylogenetic relationship supported ages as primarily due to the Dasyphyllum + 1Email: [email protected].

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