Early evolution of the angiosperm clade Asteraceae in the Cretaceous of Antarctica

Significance

The flowering plant family Asteraceae (e.g. sunflowers, daisies, chrysanthemums), with about 23,000 species, is found almost everywhere in the world except in Antarctica. Asteraceae (or Compositae) are regarded as one of the most influential families in the diversification and evolution of a large number of animals that heavily depends on their inflorescences to survive (e.g. bees, hummingbirds, wasps). Here we report the discovery of pollen grains unambiguously assigned to Asteraceae that remained buried in Antarctic deposits for more than 65 million years along with other extinct groups (e.g. Dinosaurs, Ammonites). Our discovery drastically pushes back the assumed origin of Asteraceae, because these pollen grains are the oldest fossils ever found for the family.

Abstract

The Asteraceae (sunflowers and daisies) are the most diverse family of flowering plants. Despite their prominent role in extant terrestrial ecosystems, the early evolutionary history of this family remains poorly understood. Here we report the discovery of a number of fossil pollen grains preserved in dinosaur-bearing deposits from the Late Cretaceous of Antarctica that drastically pushes back the timing of assumed origin of the family. Reliably dated to ∼76–66 Mya, these specimens are about 20 million years older than previously known records for the Asteraceae. Using a phylogenetic approach, we interpreted these fossil specimens as members of an extinct early diverging clade of the family, associated with subfamily Barnadesioideae. Based on a molecular phylogenetic tree calibrated using fossils, including the ones reported here, we estimated that the most recent common ancestor of the family lived at least 80 Mya in Gondwana, well before the thermal and biogeographical isolation of Antarctica. Most of the early diverging lineages of the family originated in a narrow time interval after the K/P boundary, 60–50 Mya, coinciding with a pronounced climatic warming during the Late Paleocene and Early Eocene, and the scene of a dramatic rise in flowering plant diversity. Our age estimates reduce earlier discrepancies between the age of the fossil record and previous molecular estimates for the origin of the family, bearing important implications in the evolution of flowering plants in general.

Flowering plants underwent a rapid ecological radiation and taxonomic diversification in the Early Cretaceous, about 121–99 Mya (1). Asterids, in particular, represent an extraordinarily diverse clade of extant angiosperms that includes more than 80,000 species. This clade contains the most species-rich angiosperm family, the Asteraceae, with 23,000 species, many of which are economically important taxa, such as sunflowers, lettuce, and gerberas. The origin and early diversification of family Asteraceae were important events in the history of life largely because this lineage has been a dominant component for the past several millions of years in numerous biomes around the world, primarily in open habitat ecosystems. Particularly, the evolution of Asteraceae, typically characterized by bearing attractive inflorescences (or capitula), may have promoted the radiation of insect pollinators (e.g., solitary bees) that heavily rely on this family to feed and reproduce (2). To date, the oldest fossil confidently assigned to Asteraceae is from the Middle Eocene of Patagonia. It consists of an inflorescence and associated pollen grains assigned to an extinct clade of Asteraceae, phylogenetically placed at a moderately derived position within the phylogenetic tree of the family (3). The discovery of these Eocene specimens indicated that the crucial split between subfamily Barnadesioideae, the earliest diverging branch of the family, and the rest of Asteraceae occurred even earlier, either during the early Paleogene or Late Cretaceous (4, 5). Recent molecular dating analyses support a Late Cretaceous origin for the crown group Asterales (4, 6), whereas the emergence of Asteraceae was estimated to have occurred in the Early Eocene (4).

Here we report fossil pollen evidence from exposed Campanian/Maastrichtian sediments from the Antarctic Peninsula (Fig. 1, Fig. S1, and SI Materials and Methods, Fossiliferous Localities) (7) that radically changes our understanding of the early evolution of Asteraceae.

Fig. 1.

Map showing distribution of Upper Cretaceous rocks of the Snow Hill Island and López de Bertodano Formations. The studied sections in Brandy Bay–Santa Marta Cove (James Ross Island) and Cape Lamb (Vega Island) are also indicated. Adapted from Olivero (7).

Fig. S1.

Stratigraphic sections of the Upper Cretaceous Snow Hill Island and López de Bertodano Formations. (A) Stratigraphic section of the Snow Hill Island Formation at Santa Marta Cove, James Ross Island with the situation of the studied samples and Ammonite Assemblages [Assemblages 8–9, adapted from Olivero (7)]. (B) Stratigraphic section of the Snow Hill Island and López de Bertodano Formations at Cape Lamb, Vega Island with the situation of the studied samples. To highlight the stratigraphic continuity of the samples, the lower 100 m of the section includes the Gamma Member of the Snow Hill Island Formation exposed on Humps Island, which bear the same Ammonite Assemblages 8-2 and 9 (Assemblages 8-2 and 9) recorded in Santa Marta Cove area (see A).

SI Materials and Methods

Fossiliferous Localities.

Samples were collected by E.B.O. in Snow Hill Island and López de Bertodano Formations on James Ross and Vega islands, Antarctica (Fig. 1) during several summer field trips. These units constitute the middle and upper parts (Campanian–Danian) of the Marambio Group, which include two major shallowing-upwards depositional sequences (1). These sequences are denominated the NG Sequence (Snow Hill Island and Haslum Crag Formations, mid–late Campanian–early Maastrichtian) and the MG Sequence (López de Bertodano Formation, early–late Maastrichtian–Danian).

In the studied section near Santa Marta Cove, James Ross Island, the outcrops of the Snow Hill Island Formation are included in the Gamma Member. This member consists of a lower sandstone-dominated package with lenticular coquinas, approximately 120 m thick, and an upper mudstone-dominated package, approximately 50 m thick (Fig. S1A). Both packages represent the transgressive system tract of the NG Sequence, with proximal, sandstone-dominated shore–face deposits at the base, followed by prodelta mudstones interbedded with sandy tempestites at the top (7). The lower package of the Gamma Member bears important fossil vertebrates, including a partial skeleton of the ankylosaur Antarctopelta oliveroi (30) and the ornithopod Trinisauras antamartaensis (31). Ammonites are scarce, but the basal conglomerate bears a reworked ammonite fauna, including diagnostic mid Campanian taxa, such as Baculites subanceps, Metaplacenticeras subtilistriatum, and Hoplitoplacenticeras sp., and several horizons, including the kossmaticeratid Neograhamites primus, which defines the mid–Campanian Ammonite Assemblage 8-1 (7). The studied samples in this package were recovered within the Ammonite Assemblage 8.1 Neograhamites primus, and include samples D8-1, D10-8, D11-1, D12-8, and D13-3b (Fig. S1A). The upper mudstone-dominated package of the Gamma Member is more fossiliferous and bears, in stratigraphic order, the Ammonite Assemblage 8-2 Neogramites cf kiliani, late Campanian, and the Ammonite Assemblage 9 Neograhamites–Gunnarites, latest Campanian–early Maastrichtian. The studied samples 14S-4d, Hy-20, and Hy were recovered within the Ammonite Assemblage 8-2, and the sample 14S within the Ammonite Assemblage 9 (7) (Fig. S1A).

The mudstone-dominated package of the Gamma Member crops out also on Hump Island and southern Cape Lamb on Vega Island (7). At Cape Lamb, it is transitionally covered by a coarsening-upward succession of silty mudstones and sandstones referred to the Cape Lamb Member of the Snow Hill Island Formation (7). The Cape Lamb Member is interpreted as a prograding deltaic wedge (7). The ammonite genus Gunnarites is very abundant throughout the member characterizing the Ammonite Assemblage 10 Gunnarites of early Maastrichtian (latest Campanian?) age (ref. 7 and references therein). The studied samples V6-10 and V8-8 were recovered from this interval (Fig. S1B). In Cape Lamb, Vega Island, the Snow Hill Island Formation is unconformably covered by the López de Bertodano Formation (Fig. S1B). The López de Bertodano Formation consists of a basal conglomerate followed by a mudstone-dominated succession with abundant ammonites, dominated by Maorites densicostatus, which are interpreted as offshore deposits representing a transgressive system tract. Based on sequence stratigraphy (7), these offshore mudstones are correlated with the late Maastrichtian deposits of the López de Bertodano Formation on Seymour Island, which bear the Ammonite Assemblages 12, 13, and 14 of Olivero (7). The studied samples V10-12, and V10-24 were recovered from the mudstone-dominated interval of the López de Bertodano Formation (Fig. S1B). The upper part of the López de Bertodano Formation at Cape Lamb consists of regressive sandstone and conglomerates included in the Sandwich Bluff Member of latest Maastrichtian age (32). Thin conglomerates at the top, possibly Paleocene, were referred to the Sobral Formation (33).

Fossil Pollen Morphotypes.

The samples were treated following standard palynological techniques (34). Fossil pollen grains were examined under transmitted white light with a Leica microscope and photomicrographs were taken with a Leica camera DFC 290. SEM photographs were included to illustrate the superficial morphological features of the pollen morphotypes. Specimen coordinates are referred to the England Finder. Pollen terminology follows Punt et al. (35).

Extant Reference Samples.

Pollen characters were obtained from the examination of slides of acetolyzed pollen grains from 368 species representing all families of extant Asterales. Pollen of Ilex, chosen as an outgroup taxon, was also included. The specimens are deposited in the herbaria ALCB, B, BAF, C, CANB, CBG, FM, G, GÖTT, HAC, HAJB, HUT, K, LP, MO, S, US, WIS (sweetgum.nybg.org/ih/). Most pollen slides were used in previous studies, mainly those of Asteraceae (36–41), but additional specimens were included. For the specimens examined specifically for the present study under scanning electron microscope, pollen grains were acetolyzed (42), suspended in 90% (vol/vol) ethanol, and mounted on stubs. The samples were sputter-coated with gold-palladium and details of the exine sculpture were examined using a JEOL JSM T-100 SEM. A list of the specimens investigated is provided in Supporting Data, below. Additional information was obtained from the literature (Supporting Data).

Estimation of Divergence Times.

We selected two fossil taxa for the estimation of the divergence times for the Asteralean lineages: one pollen morphotype placed on the phylogenetic tree using characters of extant clades (Tubulifloridites lilliei type A), and one macrofossil (capitulum) and associated pollen (Raiguenrayun cura + Mutisiapollis telleriae) related to extant Asteraceae (3, 5). Finally, the origin of the crown eudicots with fossil records (tricolpate pollen) near the late Barremian/early Aptian was used as a maximum age constraint (ref. 43, and references therein) on the root node of the phylogenetic tree (Table S4). The geologic age of each fossil was determined with precision. All stratigraphic ages were converted into absolute ages by using the geological timescale of Gradstein et al. (44). The late Campanian-early Maastrichtian to late Maastrichtian age range of the fossil T. lilliei type A translated into an absolute age of 76.4–72.1/66.0 Ma. This fossil provides a safe minimum age of 72.1 Myr for node A (Fig. S6 and Table S4).

Fig. S6.

Placement of the fossils used in the calibration scenario 1. Fossils A (T. lilliei type A) is an extinct species of Dasyphyllum in the Crown Group 3 and hence we used the age of this Fossil A to calibrate the split between Dasyphyllum and its sister genus Barnadesia. Fossils B (Raiguenrayun cura + Mutisiapollis telleriae) are extinct taxa that we identified as stem relatives of Crown Group 1. We used its age to calibrate the split between Crown Group 1 (Stifftioideae; Wunderlichioideae; Gochnatioideae; Hecastocleidoideae; Carduoideae subfamilies and rest of Asteraceae) and Crown Group 2 (Onoserideae; Mutisioideae; Nassauvieae subfamilies). Barn., Barnadesioideae; Card., Carduoideae; F., Famatinanthoideae; Goch., Gochnatioideae; H., Hecastocleidoideae; Mut., Mutisieae; Nass., Nassauvieae; On., Onoserideae; Stiff., Stifftioideae; Wund., Wunderlichioideae.

We explored a number of alternative calibration scenarios based on the position of T. lilliei type A in the backbone tree of Asterales (Fig. 2, Fig. S5, and Table S1). The most parsimonious reconstruction placed this fossil within the extant genus Dasyphyllum (Fig. 2). We also studied other possible placements of T. lilliei type A by randomly sampling all 26 characters from our original matrix with replacement (5,000 replicates) with the aim of simulating the variability that we would get if we could have sampled more characters. The resulted bootstrap consensus tree placed T. lilliei type A next to all living Asteraceae (Fig. S5A and calibration scenario 2 in Table S2) as an extinct stem relative. The age of the origin of the crown Asteraceae occurred during the Late Cretaceous either using T. lilliei type A as a crown relative (i.e., nested within Dasyphyllum) (Fig. 5 and calibration scenario 1 in Table S2) or as a stem relative (i.e., sister to all Asteraceae) (Fig. S5A and calibration scenario 2 in Table S2). We also analyzed the impact on the age of origin of Asteraceae, MGCA (Menyanthaceae, Goodeniaceae, Calyceraceae, and Asteraceae) and Asterales when calibrating the tree using the deepest placements in next-best parsimonious positions (MP+1 and MP+2) of the parsimony analysis (Fig. S5 B–E and calibration scenarios 3–6 in Table S2).

Fig. 2.

Phylogenetic analyses of the fossil taxa. Branching positions of the fossil T. lilliei type A mapped onto a backbone tree derived from a molecular analysis of Beaulieu et al. (4), with some asteracean taxa added, following a recent comprehensive analyses of Panero et al. (24). Thicker black lines indicate the most parsimonious (MP), one step less parsimonious (MP + 1), and two steps less parsimonious (MP + 2) positions for T. lilliei type A. Letters indicate the nodes used to calibrate alternative scenarios, A: Fig. 5; B–E: Fig. S5 and Table S2.

Fig. S5.

Timing of diversification of Asterales using different calibration scenarios. Chronograms (A–E, scale at the bottom in Mya) estimated using a Bayesian relaxed clock calibrated with a previously described fossil inflorescence and pollen from the Eocene (crown Asteraceae, except Barnadesioideae and Famatinanthoideae) and the oldest eudicot records (ref. 43, and references therein) from the Cretaceous (see Table S4). Our newly discovered specimens from the Cretaceous of Antarctica (red arrow) were used to calibrate alternative nodes according to the results of our sensitivity analysis (see SI Materials and Methods, Estimation of Divergence Times, and Table S2).

Fig. 5.

Evolutionary timescale of the diversification of Asteraceae. Chronogram (scale on the right in Mya) estimated using a Bayesian relaxed clock calibrated with a previously described fossil inflorescence from the Eocene (“B”) and our newly discovered specimens from the Cretaceous of Antarctica (“A”). We assume that this Cretaceous species (T. lilliei type A) represents an extinct branch nested within Dasyphyllum (crown representative). Other possible calibration scenarios are illustrated in Fig. S5. Light-blue bars at nodes represent 95% credibility intervals on estimates of divergence times. Orange horizontal lines indicate the timing of the K–P extinction event and the Cenozoic’s warmest interval. Most subfamilies of Asteraceae diverged during the Paleogene, but the earliest divergence occurred in the Late Cretaceous. B., Barnadesia; Barn., Barnadesioideae (91 species); Card., Carduoideae (2,500+ species); D., Dasyphyllum; F., Famatinanthoideae (1 species); Goc., Gochnatioideae (90 species); H., Hecastocleidoideae (1 species); Mut., Mutisieae (254 species); Nass., Nassauvieae (313 species); On., Onoserideae (52 species); S., Schlechtendalia; Stiff., Stifftioideae (44 species); Wund., Wunderlichioideae (41 species); rest of Asteraceae (19,600 + species).

Results and Discussion

The pollen grains reported here and discovered in the Late Cretaceous of Antarctica are tricolporate, microechinate, with long colpi and rimmed margins. We placed these specimens within the wide-ranging variable fossil species Tubulifloridites lilliei (Couper) Farabee and Canright previously recorded in a restricted time interval within the Late Cretaceous of western Gondwana (8, 9) (see also Supporting Data, Systematic Remarks). It has been botanically related to a number of eudicot families (Supporting Data, Systematic Remarks; see also Figs. S2B and S3F for comparison) based on superficial similarities of the pollen grains or considered as an angiosperm of uncertain position (9). We assembled our specimens from Antarctica as a subgroup of the polymorphic T. lilliei that here we informally denominate as T. lilliei type A, which is distinguished from other T. lilliei specimens by several specific morphological characters (e.g., clearly tricolporate pollen grains with well-defined lalongate ora and intercolpal depressions) (see Supporting Data, Systematic Remarks for a full description). Morphologically identical specimens of T. lilliei type A were also recovered in the Late Cretaceous of New Zealand (Fig. S4). Tubulifloridites lilliei, including T. lilliei type A, disappeared almost simultaneously from Antarctica, Australia, Patagonia, and New Zealand about 66 Mya (K/P boundary) (see Supporting Data, Systematic Remarks).

Fig. S2.

Extant species of Campanulaceae and Ranunculaceae that bear superficial similarities with the fossil T. lilliei type A. (A) Canarina canariensis (L.) Vatke shows a general resemblance to T. lilliei. (B) Clematis montevidensis Spreng., family Ranunculaceae, has been previously considered related to T. lilliei. Both Canarina and Clematis, show marked differences in exine structure and sculpture. Note the clearly columellate exine structure (see Supporting Data, Systematic Remarks). (Scale bars, 5 µm.)

Fig. S3.

Details (SEM) of the fossil T. lilliei type A from the Late Cretaceous of Antarctica and extant representatives of Asteraceae, Campanulaceae, and Ranunculaceae. (A and D) Specimens of Tubuliflorides lilliei type A (blue frames). (A) Poorly defined intercolpal depression (arrowhead); (D) detail of sculpture, note microspine (arrowhead) and bacula. (B and E) Extant Dasyphyllum inerme (Barnadesioideae subfamily, Asteraceae, pink frames). (B) Well-defined intercolpal depression (arrowhead); (E) microspines and baculum (arrowhead). (C) Canarina canariensis (L.) Vatke (Campanulaceae, green square), verrucate-perforate sculpture. (F) Clematis montevidensis (Ranunculaceae, green square) details of the microechinate- microgranulate-punctate sculpture. (Scale bars, 2 µm.)

Fig. S4.

Specimens of Tubulifloridites lilliei (Couper) Farabee & Canright from the Late Cretaceous of New Zealand that bear strong similarities with T. lilliei type A. (Supporting Data, Systematic Remarks). Specimens on slide L5664/3 (Paparoa Coal Measures, Westland Plate VI, figures 17–18 in ref. 8). (A) Specimens in equatorial view with a poorly defined intercolpal depression (arrowhead), L40(1). (B) Specimen in subpolar view, Q40(0). (Scale bars, 5 µm.)

Using an apomorphy-based method [in the sense of Sauquet et al. (10)] as a first attempt at comparing the Antarctic fossils (T. lilliei type A) and the pollen produced by extant eudicots (all supported by a single morphological synapomorphy: triaperturate pollen), we found strong morphological similarities between T. lilliei type A and some members of Asterales (Supporting Data and Figs. S2A and S3C). We explored further the phylogenetic placement of T. lilliei type A within Asterales in a parsimonious framework by using a matrix of pollen morphological characters (Supporting Data, List of Characters and Character State Definitions Used to Compile a Matrix Used as Input in Parsimony Analyses Aimed at Placing the Fossil Taxa and Table S1) and a phylogenetic tree of Asterales as backbone constraint (Fig. 2). After conducting a sensitivity analysis (see SI Materials and Methods, Estimation of Divergence Times) we found one position suitable for calibration based on the single most-parsimonious tree (188 steps). This single most-parsimonious tree places T. lilliei type A within Dasyphyllum of the Barnadesioideae (Fig. 2), the earliest diverging subfamily of the Asteraceae; the fossil possesses most of the derived morphological character states of the Dasyphyllum pollen (Figs. 3 and 4 and Fig. S3 A, B, D, and E). We also explored other scenarios, assuming T. lilliei type A was either an extinct stem relative of Asteraceae or more closely related to other members of the Asterales (Fig. S5 and Table S2). Here, we discuss the age of the origin of the daisy family considering T. lilliei type A as a crown group member (i.e., nested within Dasyphyllum).

Fig. 3.

Fossil and extant representatives of Asteraceae observed by light microscopy. (A, B, D, E, G, H) Specimens of Tubulifloridites lilliei type A from the Late Cretaceous of Antarctica (blue frames). Specimens on slide BAPal. ex CIRGEO Palin 963b; (A and B) N42(4); (D and E) L36(0); (G and H) P57(1). (A, B, D, E) Equatorial view. (G and H) Subpolar view. (A and B) Exine thickened at the poles (arrowhead). (A, E, and H) Microechinate-baculate sculpture. (D and E) Thickened exine at apertures level (arrowhead). (B, G, and H) Poorly defined intercolpal depressions (arrowhead). (G and H) Rounded colpi ends. (C, F, and I) Pollen of extant species for comparison (pink frames). (C and I) Extant Dasyphyllum inerme (Rusby) Cabrera, with well–defined intercolpal depressions and rounded colpi ends comparable to those of T. lilliei type A (arrowheads). (F) Extant Dasyphyllum velutinum (Baker) Cabrera, with microechinate-baculate exine surface similar to that of T. lilliei type A. (Scale bars, 5 µm.)

Fig. 4.

Fossil and extant representatives of Asteraceae observed by scanning electron microscopy. (A, D, E, G) Specimens of Tubulifloridites lilliei type A from the Late Cretaceous of Antarctica (blue frames). (A) Subpolar view showing details of sculpture and poorly defined depressions (arrowhead); note the microgranulate apertural membrane. (D) Subequatorial view showing a poorly defined depression (arrowhead). (E) Polar view with small apocolpium and thickened colpi margins. (G) Equatorial view showing the microechinate-baculate-verrucate sculpture. (B) Specimen of Quilembaypollis tayuoides Barreda and Palazzesi from the Miocene of Patagonia (light blue frame) that shares morphological features with both the Cretaceous and extant asteraceous specimens; note the microechinate-baculate sculpture. (C, F, H, I) Extant species of Dasyphyllum (pink frames) showing variations in the development and number of intercolpal depressions. (C and H) Dasyphyllum inerme (Rusby) Cabrera. (F) Dasyphyllum latifolium (Gardner) Cabrera. (I) Dasyphyllum leptacanthum (Gardner) Cabrera. (Scale bars, 5 µm.)

The crown of Asteraceae [i.e., the most recent common ancestor (MRCA) of the family plus all extant and extinct lineages that descended from it] is inferred to have been present from the Late Cretaceous, estimated here at 85.9 Mya [95% highest posterior density (HPD) interval: 82.3–91.5 Mya] (Fig. 5), coinciding in part with the expansion of other eudicot lineages, herbivorous and social insects, birds, mammals, and some dinosaur groups (1, 11–14). The MRCA of Asteraceae other than Barnadesioideae is estimated to have evolved about 60 Mya during the Paleocene. Interestingly, the major clades of the family diverged from this common ancestor after the K–P mass extinction event and during a relatively short time interval during the late Paleocene-early Eocene, the Cenozoic’s most pronounced warm interval (59–52 Mya) (15), which was in turn associated with a dramatic rise in flowering plant diversity and a sharp increase in insect herbivory (6, 16, 17). The analysis, assuming that the fossil is a stem relative of Asteraceae, indicated an age for Asteraceae of 67.9 Mya, also within the Late Cretaceous (Fig. S5A and Table S2).

The tolerance of some of the early diverging taxa of Asteraceae, and most members of its sister family Calyceraceae, to extreme environmental and ecological conditions leads us to believe that this resistance might have played a major role in the early evolution of Asteraceae. The earliest lineage of Asteraceae and Calyceraceae occur today in a limited number of restricted regions in South America (18), and several of their members can tolerate the extreme climatic conditions that characterize the Patagonian desert of today (e.g., intense winds, droughts, salt-sprays). Assuming that T. lilliei type A pollen grains might represent a member of the crown Barnadesioideae, their parent plants may have been able to cope with environmental stress. We infer that T. lilliei type A parent plants occupied a wide geographic range, as suggested by their distribution across western Gondwana during the Late Cretaceous, but may have become drastically reduced close to the K/P boundary, with persistence only in some areas of western Gondwana. Their descendants survived and expanded in South America, probably during the Miocene, as indicated by several fossil pollen records (19). It is assumed that plant lineages characterized by higher adaptability and increased tolerance to harsh environmental conditions (e.g., earliest branches of Asteraceae and sister Calyceraceae) were probably less affected during global extinction events. It has also been observed that the survival probability in these severe conditions would have been better for plants with polyploid genomes (20). Polyploidy is common in Asteraceae and occurs in virtually all species of subfamily Barnadesioideae (21) and family Calyceraceae (22); thus, polyploidization in the early-diverging lineages of Asteraceae may also have contributed to the survival of this group across the K–P extinction event. The pronounced climatic warming during the Late Paleocene and the Early Eocene Climatic Optimum might have also influenced the diversification of Asteraceae. We show here that most of the major lineages of Asteraceae, which mainly occur today in South America, diverged during this period of global warmth (Fig. 5) and later became isolated when cool-temperate conditions were established in the more austral regions during the Oligocene. For example, in the Guyana Highlands of northeastern South America some species of the earliest-diverging lineages (e.g., Stenopadus group) coexist as relictual patches (23). The presence in Patagonia of an Eocene inflorescence and pollen grains displaying some of the characters of this Stenopadus group (5) supports the notion that the MRCA of Asteraceae, excluding Barnadesioideae, existed in the southernmost latitudes of South America, and began to diverge and disperse northward following the equable conditions of the early Cenozoic. The global drop in temperatures during the late Cenozoic may have caused the local extinction of these Guyana Highland-centered genera from the higher latitudes and their consequent restriction in low latitudes of South America.

Our new divergence time-estimate analysis contradicts some previous assumptions about a geologically recent origin of the Asteraceae (18), indicating instead that the MRCA of the family existed far back into the Late Cretaceous. However, we also infer that the vast majority of the present-day diversity of the Asteraceae is the result of a radiation event that took place during the early Cenozoic, several millions of years after the origin of the family. This finding has important implications for our understanding of the evolution of this highly diverse and ecologically important family. The Cretaceous record from Antarctica is still poorly explored and much evidence on the early evolution of the Asterales, and potentially other groups, probably remains buried beneath present-day ice sheets. From our present knowledge, however, we estimate that the world’s highest Southern Hemisphere latitudes (i.e., Patagonia, New Zealand, Antarctica, and Australia) witnessed the emergence and early evolution of what is today the most diverse flowering plant family.

Supporting Data

Systematic Remarks.

Comments on T. lilliei (Couper) Farabee and Canright 1986.

General morphology.

This species assembles tricolporate, oblate to subspheroidal pollen grains characterized by having microechinate sculpture. The exine is faintly stratified (0.8–1.5 µm thick), the colpi are long, often with rimmed margins, and the ora are irregular in outline with ragged margins. However, this species shows variation in colpi development, density of spines and clarity of the ora (ref. 9, and references therein).

Stratigraphic distribution.

T. lilliei was widely reported in the Late Cretaceous of New Zealand, Australia, Antarctica, and southern South America [e.g., Couper (45); Raine et al. (8); Dettmann and Jarzen (9); Wilson (46); Barreda et al. (47)].

Botanical affinity.

T. lilliei was botanically related to Ranunculaceae [Clematis (45, 48)], Euphorbiaceae [Neoscortechinia (49)], or considered as an unknown angiosperm group (9).

Specimens from Antarctica.

The specimens recovered from the Campanian-Maastrichtian of Antarctica fit with the general diagnosis of T. lilliei and support the polymorphic features of this morphospecies. However, some of these specimens, in particular, show consistent and well defined characters that lead us to circumscribe them within a new morphotype that we retained within T. lilliei and informally named as T. lilliei type A. A formal definition should wait until a complete study of most T. lilliei specimens recorded in the Late Cretaceous of southern Gondwana (Australia, Patagonia, New Zealand, Antarctica) are carried out.

T. lilliei type A.

Description.

Pollen grain tricolporate, isopolar, subspheroidal to subprolate; amb circular to subcircular and elliptic outline in equatorial view. Colpi long with rounded ends and rimmed margins, colpal membrane microgranulate, ora well defined, lalongate. Exine faintly stratified (1.2–2 µm thick), thickened at poles; nexine equal to or thinner than sexine. Exine surface microechinate, sometimes interspersed with microbacula and small verrucae, 0.2–0.5 µm in basal diameter, 0.3–0.8 µm in height, and spaced 2–4 µm apart. Intercolpal depressions often present but poorly defined.

Dimensions.

Equatorial diameter 18–22 µm; polar diameter 20–25 µm.

Main studied material.

Specimens on slide BAPal. ex CIRGEO Palin 963b: N42(4), L36(0), P57(1).

Distribution.

Occurs in trace amounts in late Campanian-late Maastrichtian sequences of Snow Hill Island and Lopez de Bertodano Formations, Snow Hill and Vega Islands, Antarctica.

Remarks and comparisons.

This new type fits with the broad diagnosis of T. lilliei but it shows variations in general shape (subspheroidal to subprolate), clarity of apertures (with well-defined lalongate ora), and exine structure (thickened at poles and with intercolpal depressions). Some specimens reported from the Late Cretaceous of Paparoa Coal Measures, Westland, New Zealand (8) bear strong similarities with T. lilliei type A, as they have a thick exine and poorly defined intercolpal depressions (Fig. S4).

Botanical affinity.

Several angiosperm families produce triaperturate pollen grains with microechinate exine sculpture. Here we used the apomorphy-based method [in the sense of Sauquet et al. (10)] as a first attempt to estimate the closest living relatives of the fossil T. lilliei type A, conducting exhaustive comparisons with members of Lamiaceae, Ranunculaceae, Cleomaceae, Solanaceae, Hectorellaceae, Rhamnaceae, Euphorbiaceae, Rubiaceae, Caprifoliaceae, and families of Asterales (Stylidiaceae, Campanulaceae, Goodeniaceae, Calyceraceae and Asteraceae) by using information available in the literature (36, 50–60). Despite gross similarities, however, most of these families have significant differences in apertures, structure, or sculpture with T. lilliei type A: Lamiaceae (Clerodendrum type) are tricolpate, have short colpi, uniformly microechinate sculpture, and perforate tectum (53); Ranunculaceae (Clematis) are larger (approximately 40 µm), oblate to spheroidal, tricolpate, have a clearly columellate exine structure and variable sculpture (microechinate-microgranulate), with minutely perforate tectum (52, 54, 55); Cleomaceae (Cleome) are tricolporoidate, with thin exine (< 1 µm) and conspicuous columellae (50); Solanaceae (Latua) have indistinct ora and very thin exine (< 1 µm) (50); Hectorellaceae (Hectorella) are tricolpate, larger (approximately 40 µm), clearly columellate and with perforate tectum (54); Rhamnaceae (Pomaderris) have circular ora and sparingly perforate tectum (54); Euphorbiaceae (Neoscortechinia) differ in having shorter colpi, clearly columellate exine, and stout microspines with acute ends (57); Rubiacae, (Bikkia) have shorter colpi with poorly defined margins (56); Caprifoliaceae (Symphoricarpos, Plectritis) have tricolporate apertures, but with short colpi, clearly columellate exine, and conical microspines with acute ends (51). The strong morphological similarities from T. lilliei type A occur within the members of Asterales. In particular, the phylogenetic method we conducted to evaluate the accurate placement of the fossils from Antarctica within the order indicate the genus Dasyphyllum of the Barnadesioideae (Asteraceae) as the closest living relative of T. lilliei type A.

List of Characters and Character State Definitions Used to Compile a Matrix Used as Input in Parsimony Analyses Aimed at Placing the Fossil Taxa (Table S1).

Pollen characters are as follows: 1- Pollen units: single monads (0), tetrads (1) . 2- Pollen size (average): small (< 20 µm) (0), medium (20–40 µm) (1), large (>40 µm) (2). 3- Shape (P/E index): peroblate (0), oblate-suboblate (1), spheroidal (2), subprolate (3), prolate (4). 4- Outline in equatorial view: circular-subcircular (0), elliptic (1), rhomboid-subrhomboid (2), rectangular-subrectangular (3). 5- Outline in polar view (Amb): circular-subcircular (0), subangular (1), angular (2). 6- Aperture number: three (triaperturate) (0), many (polyaperturate) (1). 7- Aperture type: porate (0), colpate (1), colporate (2). 8- Aperture fusion: syncolpate (0), nonsyncolpate (1). 9- Endoaperture shape: circular to subcircular (0), lalongate (1). 10- Apocolpia size: small (equatorial diameter/apocolpium ratio > 5) (0), medium (equatorial diameter/apocolpium ratio between 3–5) (1), large (equatorial diameter/apocolpium ratio <3) (2). 11- Colpi ends: rounded (0) yes, acute (1). 12- Sculpture of the apertural membrane: psilate (0), microgranulate (1), scabrate (2), verrucate (3), microechinate (4). 13- Exine sculpture: microechinate (0), echinate (spines longer than 1 µm) (1), striate-rugulate (2), striate (3), clavate (4), punctate (with sparse puncta) (5), rugulate (6), verrucate (7), microgranulate (8), baculate (9). 14- Sculpture size (observations under light microscopy): sculpture visible in optical section (approximately >0.8 µm) (0), sculpture faintly visible in optical section (approximately 0.8–0.4 µm) (1), sculpture not visible in optical section (approximately < 0.4 µm) (2). 15- Tip of spine: acute (0), rounded (1). 16- Tectal surface among major sculptural elements (observations under SEM): psilate (0), scabrate (1), striate (2), microperforate (3), rugulate (4). 17- Intercolpal depressions: absent (0), present (1). 18- Intercolpal depressions development: well defined (1), poorly defined (0). 19- Columellate layer (observations under light microscopy): columellae clearly distinguishable (0), columellae poorly distinguishable (1), columellae not distinguishable (2). 20- Internal tectum: present (1) yes, absent (0). 21- Ectexine layers (observations under light microscopy): one layer (0), two layers (1), three layers (2). 22- Exine thickness at the mid–mesocolpium: ≤1 µm (0), between 1 and 3 µm (1), >3 µm (2). 23- Exine thickened at the poles: thickened (1), nonthickened (0). 24- Exine thickened at the equator: thickened (1), nonthickened (0). 25- Nexine/sexine ratio: >2 (0), between 1 and 2 (1), <1 (2). 26- Exine thickened at apertures level: thickened (1), nonthickened (0).

Details of the Extant Material Examined for Morphological Characters Provided in Data Matrix and References for Scoring.

Specimens examined specifically for the present study are identified with an asterisk (*).

Extant specimens investigated.

ALSEUOSMIACEAE: Alseuosmia. A. macrophylla A. Cunn.: *Chapman 258560 (K); A. quercifolia A. Cunn.: *Melville 1665 (K). Crispiloba. C. disperma (S. Moore) Steenis: *Arboretum 1501 (K), *Gray 1904 (K). ARGOPHYLLACEAE: Argophyllum. A. lejourdanii F. Muell.: *Forster 9487 (K). Corokia. C. buddleioides A. Cunn.: *S. Andreos s/n° (K). ASTERACEAE: Brachylaena. B. discolor DC.: Mogg 16165 (US). Chaetanthera. C. acerosa (Remy) Benth. & Hook. f.: Ruiz Leal 24661 (LP), Cabrera 3525 (LP); C. apiculata (Remy) F. Meigen: Werdermann 627 (LP), Philippi, s/n° (LP 66472); C. australis Cabrera: Böcher et al., 1658 (LP); C. brachylepis Phil.: 9842 (LP), Barros 7443 (LP); C. chilensis DC.: Barros 7441 (LP), Riera s/n° (LP 66820); C. chiquianensis Ferreyra: Cerrate 1323 (LP); C. ciliata Ruiz & Pav.: Brochers 1071c (LP), Landbeck s.n. (LP 66975); C. cochlearifolia (A. Gray) B. L. Robinson: Macbride & Featherstone 845 (LP); C. dioica (Remy) B. L. Robinson: Kurtz 13717 (LP), Jörgensen 1325 (LP); C. elegans Phil.: without leg. (ex LPS 1592 in LP), Barros 2410 (LP); C. euphrasioides (DC.) F. Meigen: Spegazzini (ex LPS 2542 in LP), Looser 5751 (LP); C. flabellata D. Don: Pisano et al., 1641 (LP), Zöllner 660 (LP); C. flabellifolia Cabrera: Werdermann 189 (LP), Rossow & Rizzo 5642 (LP); C. glabrata (DC.) F. Meigen: Looser 4389 (LP), Jiles 2363 (LP); C. glandulosa Remy: Jiles 1237 (LP); C. gnaphalioides (Remy) I.M. Johnst.: Wagenknecht 4388 (LP), Jiles 1237a (LP); C. incana Poepp. ex Less.: Jiles 2326 (LP), without leg. (LP 66959). C. lanata I. M. Johnst.: Cabrera 3550 (LP), Gijoux s.n. (LP 66804); C. leptocephala Cabrera: Muñoz & Johnson 2192 (LP); C. limbata (D. Don) Less.: Germain s/n° (LP 66884), Barros 2402 (LP); C. linearis Poepp. Ex Less.: Montero O. 293 (LP), Looser 5214 (LP); C. lycopodioides (Remy) Cabrera: Boelcke 2468 (LP), Looser 2150 (LP); C. microphylla (Cass.) Hook. & Arn.: Cabrera 11120 (LP), Mahu 1040 (LP); C. minuta (Phil.) Cabrera: Cabrera 3568 (LP), Krapovickas & Hunziker 5700 (LP); C. moenchioides Less.: without leg. (LP 67034), without leg. (LP 67033); C. pentacaenoides (Phil.) Hauman: King 336 (LP), Ruiz Leal & Roig 23617 (LP); C. peruviana A. Gray: Cerrate et al., 6490 (LP), Weberbauer 6876 (LP); C. planiseta Cabrera: without leg. (LP 66498), Barros 9849 (LP); C. pulvinata (Phil.) Hauman: Pérez Moreau 158 (LP), Ruiz Leal 3182 (LP); C. pusilla (D. Don) Hook. et Arn.: Germain s/n° (LP 66621), without leg. (LP 6371); C. renifolia (Remy) Cabrera: Philippi s/n° (LP 66746), Philippi s/n° (LP 6370); C. revoluta (Phil.) Cabrera: Cabrera 8372 (LP), Cabrera 8874 (LP); C. serrata Ruiz & Pav.: Junge 1282 (LP), Gunckel 432 (LP); C. spathulifolia Cabrera: Pérez Moreau s/n° (LP 66809), Spegazzini s/n° (ex LPS 1600 in LP); C. sphaeroidalis (Reiche) Hicken: Werdermann 253 (LP), C. splendens (Remy) B. L. Robinson: Jiles 1567 (LP), Reiche s/n° (LP 66742); C. stuebelii Hieron.: Rohmeder T–18 (LP), Krapovickas & Hunziker 5332 (LP); C. valdiviana Phil.: Philippi 1068 (LP); Barros 178 (LP). Chuquiraga. C. acanthophylla Weddell: Cabrera 7721 (LP), Cabrera 9468, 7721 (LP); C. arcuata Harling: Asplund 17679 (S); C. atacamensis Kuntze: Budins 5 (LP), Cabrera 8288 (LP); C. aurea Skottsberg: Castellanos 7927 (LP), Birabén & Birabén 1 (LP); C. avellanedae Lorentz: Boelcke 1687 (LP), Morello 34 (LP); C. calchaquina Cabrera: Novara 1123 (MCNS), 1283 (LP); C. echegarayi Hieronymus: Roig 13026 (LP), Zardini & Volponi 100 (LP); C. erinaceae D. Don.: Cabrera 9036 (LP); C. jussieui J.F. Gmelin: Cañigueral 280 (LP), Herzog 2477 (LP); G. kuschelii Acevedo: Ricardi et al., 110 (LP), Ricardi and Silva 3362 (LP); C. longiflora (Grisebach) Hieronymus: Fabris 1361, 1385 (LP), Rodríguez 1411 (LP); C. morenonis (Kuntze) Ezcurra: Ruiz Leal 26876 (LP), Ameghino s/n; C. oblongifolia Sagástegui: Sánchez et al., 6076 (HAO), Sánchez & Briones 3761 (HAO); C. oppositifolia D. Don.: Ruiz Leal 153, 27159 (LP); C. parviflora (Grisebach) Hieronymus: Schikendantz 152, 278 (LP); C. rosulata Gaspar: Cabrera 19533 (LP), Pérez Moreau 3018 (LP), Ruiz et Leal 16057 (LP), C. ruscifolia D. Don.: Ruiz Leal 1838 (LP), Botino 85 (LP); C. spinosa subs. huamapinta Ezcurra: López et al., 8327 (HUT); C. straminea Sandwith: Cabrera 20574 (LP); C. ulicina (Hook. et Arn.) Hook & Arn.: Barros 2075 (LP), Cabrera 12674 (LP); C. weberbaueri Tovar: López et Sagástegui 3229 (HUT), Sánchez Vega 1146 (LP). Cnicothamnus lorentzii Griseb.: Maldonado 408 (LP), Cabrera et al., 14497 (LP). Cyclolepis genistoides D. Don, Zardini & Kiesling 114 (LP); Ruiz Leal 4055 (LP). Dasyphyllum. D. argenteum Kunth: Rose 23055 (US), D. armatum (Koster) Cabrera: Cárdenas 4805 (US); D. brasiliense Cabrera: Glaziou 14948 (LP), Rojas 4645 (LP); D. brevispinum Sagástegui & M.O. Dillon: Sagástegui et al., 14277, 14454 (HAO); D. cabrerae Sagástegui: Díaz et al., 1105 (HUT); D. candolleanum (Gardner) Cabrera: Lima 49163 (LP); D. colombianum (Cuatrecasas) Cabrera: Killip & Smith 19690 (US); D. cryptocephalum (Baker) Cabrera: Santos Lima & Brade 14194 (LP); D. diacanthoides (Lessing) Cabrera: Cabrera 11495 (LP), Boelcke 1798 (LP); D. donianum (Gardner) Cabrera: Gardner 4946 (LP), Duarte 8169 (LP); D. excelsum (Don) Cabrera: Garavente 4146 (LP); D. ferox (Weddell) Cabrera: López 1121 (LP), Isern 475 (LP); D. flagellare (Cassaretto) Cabrera: Duarte 2633 (LP), Hatschbach 38797 (LP); D. floribundum (Gardner) Cabrera: Hassler 11251 (LP); D. horridum (Muschler) Cabrera: Weberbauer 5847 (LP); D. hystrix Weddell: López & Sagástegui 8065 (HUT), Smith et al., 12019 (HUT); D. inerme (Rusby) Cabrera: Tolaba et al., 1844 (LP), Cabrera 3100 (LP), Ragonese 268 (LP); D. infundibulare (Baker) Cabrera: Pohl 344 (K); D. lanceolatum (Lessing) Cabrera: Hoehne 2348 (BAF); D. lanosum Cabrera: Glaziou 19571 (LP); D. latifolium Rojas 10533 (LP), 10484 (LP); D. leiocephalum (Weddell) Cabrera: Samaloa 56, 68 (LP), Marín 2053 (LP); D. leptacanthum (Gardner) Cabrera: Occhioni 1023 (LP), Cabrera 12256 (LP); D. marialianae Zardini et Soria: Guerrero 13263 (MO), Soria 7047 (LP); D. orthacanthum (De Candolle) Cabrera: Glaziou 5912 (US); D. popayanense (Hieronymus) Cabrera: Lehmann 6231 (US); D. reticulatum (De Candolle) Cabrera: Pereira Duarte 2400 (LP), Hatschbach 29840 (LP); D. retinens (S. Moore) Cabrera: Malme 2117 (LP); D. spinescens (Lessing) Cabrera: Sehnen 2514 (LP), Kuhlman s/n° (LP), D. sprengelianum (Gardner) Cabrera: Duarte 2660 (LP), Hatschbach 32099 (LP); D. synacanthum (Baker) Cabrera: Rambo 45445 (LP), Reitz 1528 (LP); D. tomentosum (Sprengel) Cabrera: Hunziker 926 (LP), Rambo 47174 (LP); D. trichophyllum (Baker) Cabrera: Damazio s/n° (LP); D. vagans (Gardner) Cabrera: Glaziou 11059 (LP), Melo Barreto 3766 (LP); D. velutinum (Baker) Cabrera: Duarte 2906 (LP), Mello Barreto 10884 (LP); D. vepreculatum (D. Don) Cabrera: Williams & Alston 243 (LP), Steyermark 61092 (F); D. weberbaueri (Tovar) Cabrera: López et al., 7805 (HUT). Dicoma. D. anomala Chisumpa 26 (LP). Doniophyton. D. anomalum (D. Don) Kurtz: Buenanueva s/n° (LP); King 648 (LP); Maldonado 1448 (LP), Bonifacino et al., 96 (LP); D. weddelli Katinas et Stuessy: Ruiz Leal 2093 (LP). Gochnatia. G. arborescens T. S. Brandegee: Keid Moran 9538 (US), Spjut & Edson 6085 (US); G. argyrea (Dusén) Cabrera, Smith, Klein & Hatschbach 14460 (LP); G. attenuata (Britton) R. N. Jervis & Alain: Bisse et al. s/n° 50424 (HAJB); G. arequipensis Sandw.: Eyerden & Beetle 22120 (LP); G. barrosoae Cabrera: Macedo 5574 (US), Cabrera 12313 (LP), Mantovani 503 (LP); Mathes 3 (LP); G. boliviana S. F. Blake: Beck 6264 (LP), Herzog 1757 (LP), G. buchii (Urb.) J. Jiménez Alm.: Jiménez & Holdridge 2039 (US), Jiménez 3613 (LP), Leonard & Leonard 11858 (US); G. calcicola (Britton) R. N. Jervis & Alain: del Risco et al. s/n° (HAC 27561); G. crassifolia (Britton) R. N. Jervis & Alain: Arias et al. s/n° (HAJB 58526); G. cordata Less.: Burkart & Crespo 23169 (LP), 19951 (US); G. cowellii (Britton) R. N. Jervis & Alain: Howard 5098 (US), Ventosa s/n° (HAJB); G. cubensis (Carabia) R. N. Jervis & Alain: López Figueiras 1692 (HAC); G. curviflora (Griseb.) O. Hoffm.: Jerez et al., 4912 (LP), Fiebrig s/n° (C); G. densicephala Sancho: Assis & Williams 7393 (LP), Glaziou 11072 (K); G. discolor Baker: Clausen 1301 (NY); G. ekmanii (Urb.) R. N. Jervis & Alain: Ekman 13865 (S), Ekman 16865 (S); G. elliptica (León) Alain: Valentín Montero 21269 (HAC); G. floribunda Cabrera: Roque et al., 281 (LP); G. foliolosa (D. Don) Hook. & Arn.: Boelcke 3887 (LP), Marticorena et al., 25217 (LP), Jiles 1693 (S); G. gardneri (Baker) Cabrera: 4183 (K, G), G. glutinosa (D. Don) Hook. & Arn.: Simon & Bonifacino 509 (LP), Navarro & Bruno 9228 (S); G. gomezii (León) R. N. Jervis & Alain: León 20876 (HAC); G. hatschbachii Cabrera: Maguire et al., 49149 (US); G. haumaniana Cabrera: Maguire et al., 49194 (US), Rojas 10391 (K); G. ilicifolia Less.: Eggers 4473 (C), Small & Carter 8526 (US), Ventosa, Oviedo & Fuentes 42615 (HAC); G. intertexa (Griseb.) R. N. Jervis & Alain: Bisse et al. s/n° (HAJB 41557). G. magna Cabrera: Cronquist 11277 (NY); G. mantuensis (Griseb.) R. N. Jervis & Alain: Shafer 11208 (LP), Wright 2876 (HAC); G. microcephala (Griseb.) R. N. Jervis & Alain: Ekman H– 9280 (S); G. maisiana (León) R. N. Jervis & Alain: La Salle 17576 (HAC), G. montana (Britton) R. N. Jervis & Alain: Ekman 18725 (S); G. obovata (Urb. & Ekman) J.Jiménez Alm.: Ekman 5366 (S); G. obtusifolia (Britton) R. N. Jervis & Alain: Acuña & Díaz Barreto 17456 (HAC); G. oligocephala (Gardner) Cabrera: Menezes s/n° (59198 LP); G. orbiculata (Malme) Cabrera: Handro 156 (US); G. palosanto Cabrera, Ventura 9793 (LP), Wood 12696 (US); G. parvifolia (Britton) R. N. Jervis & Alain: Bisse et al. s/n° (HAJB 38075); G. patazina Cabrera: Velande Nuñez 3178 (LP); G. pauciflosculosa (Wight) R. N. Jervis: Eggers 3866 (C), Brace 4019 (US); G. picardae (Urb.) J. Jiménez Alm.: Ekman 5385 (US); G. polymorpha (Less.) Cabrera: Harley et al., 26 497 (US), Woolston 808 (S), Blanchet 3251 (LP), Glaziou 3039 (LP); G. ramboi Cabrera: Rambo 51161 (LP); G. recurva (Britton) R. N. Jervis & Alain: Bisse et al. s/n° (HAJB 21657), Alvarez et al. s/n° (HAJB 56472), Acuña 12788 (US); G. rotundifolia Less.: Hoehne 3411273 (US), Brade 5346 (S); G. sagreana R. N. Jervis & Alain:, Britton et al., 13981 (US), Bisse et al. s/n° (HAJB 42105); G. shaferi (Britton) R. N. Jervis & Alain:, Bisse et al. s/n° (HAJB 35368); G. tortuensis (Urb.) J. Jiménez Alm.: Ekman H–4313 (S); G. vernonioides Kunth.: López et al., 3354 (LP), Becker & Torrones 1391 (US), López Sagástegui 3354 (LP): Hecastocleis shockleyi A. Gray: Train 3973 (LP), A. Kellog 5301 (US). Hyalis argentea D. Don: Daciuk (LP), *Pertusi 259 (LP). Mutisia. M. acerosa Poepp.: Cabrera 3463 (LP); M. acuminata var. paucijuga: Cabrera et al., 13894 (LP); M. alata Hieron.: A. López et al., 6719 (LP); M. andersonii Sodiro: Scolniek 1532 (LP); M. arequipensis Cabrera: Treacy 840, 829 (WIS); M. brachyantha Phil.: Wederman 541 (LP); M. campanulata Less.: G. Hatschbach 4058 (LP); M. cana Poepp. Et Endl.: Jiles 2710; M. clematis L.: F. Fosberg 22294 (LP); M. coccinea St. Hil.: Krapovickas et al., 22993 (LP); M. cochabambensis Hieron.: Cañigueral 11 (LP); Zamaloa 2033 (LP); M. comptoniafolia Rusby: Krach 7178 (SI); M. decurrens Cav.: Grüner 132 (LP), Soriano 4294 (LP); M. friesiana Cabrera: Cabrera et al., 22501 (LP); M. hamata Reiche: Cabrera et al., 22495 (LP); M. homoeantha Wedd.: Meyer 17565 (LP); M. ilicifolia Phil: Jiles 1871 (LP); M. involucrata Phil.: Barros 3804 (LP); M. latifolia D. Don.: Jiles 3139 (LP); M. ledifolia Decaisne: Cabrera 9438 (LP); M. kurtzii: Fabris et al., 4082 (LP); var. anomala: Cabrera 9001 (LP), Rodríguez 320 (LP); M. linearifolia Cav.: Marticorena & Matthei 947 (LP); M. linifolia Hook.: Dawson & Pujals 1611 (LP);); M. macrophylla Phil.: Barros 7552, 1772 (LP); M. mandoniana Wedd.: Beck & Seidel 14549 (SI); G. & D. Schmitt 123 (FM); Cárdenas 4869 (FM); M. manigera Wedd.: Riccardi & Marticorena 25468 (LP); M. mathewsii var. anomala Cabrera: Macbride & Featherstone 907 (LP); M. retrorsa M. A. Vignati 420 (LP), M. saltensis Cabrera: Cabrera et al., 25519 (LP). M. sinuata Cav.: Fabris & Marchionni 2344 (LP), King 334 (LP), Ruiz Leal 2146 (LP); M. spectabilis Phil.: C. Jiles P. 1834 (LP); M. subspinosa Cav.: Ruiz Leal 1051 (LP); Villavicencio, O'Donell 1331(LP); M. subulata R. & P.: Jiles 4189, 2586 (LP); M. orbignyana Wedd.: Meyer, Cuezzo & Legname 20888 (LP), Isern 394 (LP); M. grandiflora Humb. & Bonpl.: Cuatrecasas 20917 (FM), Acosta Solís 5442 (FM); M. hamata Reiche: Cabrera et al., 22495 (LP); M. intermedia Hieron.: Sodiro (BAF); M. lanata Weddell 2314 (LP); Scolnik & Luti 519 (LP); M. lehmannii Hieron.: Jaramillo 5415 (FM), Dorr & Valdespino 6382 (FM); M. microphylla Willd ex C.D.: Sodiro (BAF); Zak 715 (FM), Romoleroux 297 (FM), Firmin 524 (FM); M. oligodon Popp. Et Endl.: Cabrera 6090 (LP), Ledezma 650 (LP); M. pulcherrima Muschl.: Sagástegui 7469 (LP); M. retrorsa Cav.: M. A. Vignati 420 (LP); M. rimbachii Sodiro ex Harris: Villacrés 234 (FM); M. sodiroi Hieron.: Sodiro (BAF), Fosberg 21188 (FM); M. speciosa Ait.: Grüner 1077 (LP), Rodríguez 1265 (LP), T. Rojas 4042 (LP); M. spectabilis Phil.: Carlos Jiles 1834 (LP), Zorrilla & Jiles 1816 (LP); M. spinosa R. & P.: Hollermayer 725 (LP); M. stuebelii Hieron.: Cuatrecasas 19156 (FM). M. venusta Blake: Vargas 4420 (LP); M. vicia Koster: 2256 (LP); M. wurdackii Cabrera: López, Sagástegui & Kollantes 4303 (LP). Onoseris. O. alata Rusby: Cabrera 15862 (LP); Cabrera et al., 14525 (LP); O. odorata Hook. & Arn.: Scolnick 1013 (LP); Cabrera & Fabris 13427 (LP). Perezia. P. atacamensis (Phil.) Reiche: *Cabrera et al., 22482 (LP); P. bellidifolia (Phil.) Reiche: *Eskuche 599–20 (LP); P. recurvata Less.: *1493 (LP). Pertya. P. scandens (Thunb. Ex Thunb) Sch. Bip.: Steward & Cheo 972 (NY); P. discolor Rheder: Smith 5786 (MO). Proustia. P. cuneifolia D. Don: Burkart & Troncoso 11974 (LP), *Fabris & Zuloaga 8466 (LP). Stenopadus. S. huachamacari Maguire: Maguire et al., 30116 (MO); S. affinis Maguire et al.: Liesner 18346 (MO); S. connellii (N.E.Br.) S. Blake: Liesner 23109 (MO); Schlechtendalia. S. luzulaefolia Less.: Rosengurtt B–4507 (LP); *Pereira 8490 (LP). Senecio.* S. pampeanus Boffa 1087 (LP). Stifftia. S. chrysantha J.C. Mikan: Cabrera 12242 (LP). S. parviflora (Leandro) D. Don: Hering 7680 (LP); S. uniflora Ducke: Ducke s/n° (LP). Tarchonanthus. T. camphoratus Regmen 501 (US). Wunderlichia. W. azulensis Maguire & G.M. Barroso: Harleg et al., 25209 (MO); W. crulsiana Taubert: Ratter et al., 2615 (MO); W. mirabilis Riedel ex Baker: Ratter et al., 2621 (MO). CAMPANULACEAE: Canarina. C. campanula (L.) Vatke: *s/n° (GÖTT). Campanula. C. barbata L.: *Pedersen 6779 (LP).

CALYCERACEAE: Boopis. B. anthemoides Juss.: *Bottino 437 (LP). bM. fuensis: *Neumeyen n° 20 (LP). ESCALLONIACEAE: Carpodetus. C. arboreus (Lauterb. & K. Schum.) Schltr.: *30638 (K); C. major Schltr.: *Regdado 1145 (K). Pentaphragma. P. decurrens Airy Shaw: *Christensen 1055 (K). GOODENIACEAE: Coopernookia. C. polygalaceae (de Vriese) Carolin: *Jackson 1432 (CANB). Dampiera. D. lanceolata A. Cunn.: *Wheeler 454 (GÖTT). Goodenia. G. ovata Sm.: *Wolls (GÖTT); G. incana R. Br.: *Von Müeller (GÖTT). ICACINACEAE: Ilex. I. paraguarienses A. St.–Hil.: *Zardini et al., 727 (LP). MENYANTHACEAE: Menyanthes. M. trifoliata L.: *2263, Vöhrnm (Gött). Nymphoides. N. aquatica (J.F. Gmel.) Kuntze: *Nelson 23881 B); N. brevipedicelata (Vatke) A. Raynal: *4576 (B); N. peltata (s.G. Gmel.) Kuntze: *Fratiles (B). Liparophyllum. L. capitatum (Ness) Tippery & Les.: *Pritzel 108 (B). RANUNCULACEAE: Clematis. C. montevidensis Spreng.: *Torres Robles 1613 (LP). ROUSSEACEAE: Abrophyllum. A. ornans var. microcarpum F.M. Bailey: *Wannana (K), Arboretum (K). Cuttsia. C. viburnea F. Muell.: *Telford 2623 (CBG). Roussea. R. simplex Sm.: *Botana 1483 (K). STYLIDIACEAE: Levenhookia. L. preisii (Sond) F. Muell.: *Wrigley s/n° (CBG); L. stipitata F. Muell. Phyllachne. P. uliginosa J.R. Forst & G. Forst: *Reed s/n° (K). Stylidium. S. inundatum R. Br.: *Kenneally 11435 (CANB); S. preissii (Sond) F. Muell.: *Carquist 4013 (CANB).

Specific literature used.

Karehed, 1965 (61); Karehed et al., 1999 (62); Rowley and Nilsson, 1972 (63); Bronckers and Stainier, 1972 (64); Nilsson, 1973 (65); Martin, 1977 (66); Lobreau-Callen, 1977 (67); Skavarla et al., 1977 (51); Ferguson and Hideux, 1978 (68); Dunbar 1978 (69); Praglowsky and Grafström, 1985 (70); Cilliers, 1991 (71); Hansen, 1991 (72); Moar, 1993 (54); Gustafsson et al., 1997 (59); Urtubey and Tellería, 1998 (36); Lundberg, 2001 (73); Tellería et al., 2003 (74), Tellería et al., 2013 (41); Tellería, 2008 (37); Polevova, 2006 (75); Wortley et al., 2007 (76); DeVore et al., 2007 (60); Blackmore et al., 2010 (77); Pereira Coutinho et al., 2012 (78); Hong and Pan, 2012 (58); Freire et al., 2014 (79).

Materials and Methods

Fossil Samples.

Rock samples were recovered from the Campanian/Maastrichtian Snow Hill and López de Bertodano Formations on the James Ross and Vega islands, in Antarctica by E.B.O. Samples were chemically treated following standard palynological techniques (SI Materials and Methods, Fossiliferous Localities and Fossil Pollen Morphotypes, and Fig. S1). The slides are housed in the palynological collection of the Museo Argentino de Ciencias Naturales (Buenos Aires, Argentina): BAPal, ex CIRGEO Palin 605–613, 962–965.

Phylogenetic Placement of the Fossil.

The apomorphy-based method was used first to compare the fossil T. lilliei type A with extant angiosperm families, particularly those having triaperturate microechinate pollen grains (e.g., Ranunculaceae, Rubiaceae, Euphorbiaceae, Campanulaceae, Calyceraceae, Asteraceae) by using information available in the literature. We observed strong morphological similarities between T. lilliei type A and some members of Asterales. To increase the taxonomic resolution of this assignment we conducted a parsimony analysis to evaluate the placement of the fossils from Antarctica within the order. Pollen characters for 55 extant species of Asterales were scored (SI Materials and Methods, Extant Reference Samples, and Supporting Data, List of Characters and Character State Definitions Used to Compile a Matrix Used as Input in Parsimony Analyses Aimed at Placing the Fossil Taxa and Details of the Extant Material Examined for Morphological Characters Provided in Data Matrix and References for Scoring). The morphological matrix comprises 26 binary and multistate pollen characters, and 55 taxa chosen to represent all families and tribes in Asterales, along with one outgroup taxon, Ilex from family Aquifoliaceae (Supporting Data, Details of the Extant Material Examined for Morphological Characters Provided in Data Matrix and References for Scoring and Table S1). We used a backbone tree derived from a molecular analysis of Beaulieu et al. (4), with some additional taxa, following the recent comprehensive analysis of Panero et al. (24). We conducted the analyses using the parsimony criterion as implemented in the software PAUP (25), enforcing the topological constraint, with the heuristic search option of 1,000 random addition replicates and tree bisection and reconnection branch swapping. Alternative phylogenetic positions of T. lilliei type A were evaluated by searching for the bootstrap consensus tree, the most parsimonious tree, and by searching for trees one and two steps longer than the most parsimonious tree (SI Materials and Methods, Estimation of Divergence Times) and by assigning the fossil manually to different branches with MacClade (26), following the approach of Doyle and Endress (27).

Divergence Time Estimates.

We selected DNA sequences of 101 species of Asteraceae, with an additional 36 species used as outgroup taxa. Three protein-coding genes from the plastid genome (ndhF, rbcL, matK) were obtained for all taxa from GenBank (Table S3). Alignment of individual regions was completed using default settings in MAFFT v.7 (28).

Divergence time estimates and phylogenetic relationships were inferred using Markov Chain-Monte Carlo methods implemented in BEAST2 (29). A GTR + Γ substitution model applied to the entire dataset, and the birth–death model of speciation and an uncorrelated lognormal-relaxed molecular clock model were used. Prior distributions on the root and two other nodes were applied based on the interpretation from the fossil record of Asteraceae. A complete list of the fossil species used to calibrate the tree, geologic ages, and citations is given in Table S4 and Fig. S6, and a list of the explored calibration scenarios is given in Table S2 and illustrated in Fig. S5. We ran four independent chains for each calibration scenario, each for 100 million iterations, sampling every 1,000th generation using the CIPRES Science Gateway. The program Tracer (29) was used to confirm that the four independent runs converged on the same stationary distribution. Post burn-in samples from the marginal posterior distribution were combined using LogCombiner v1.5.4 (29) and trees summarized with TreeAnnotator (29). The topology of the tree broadly corresponds with that obtained by Panero et al. (24).