# Past aridity and dust drove biodiversity crises and altered pollination in the ancient gymnosperm (Gnetales)

Natasha Barbolini, Niels Meijer, Carina Hoorn, Guillaume Dupont-Nivet, Fang Han, Ashley Krüger, Qin Yuan, Alexander Rohrmann, Kristina Bolinder, Catarina Rydin

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Natasha Barbolini, Niels Meijer, Carina Hoorn, Guillaume Dupont-Nivet, Fang Han, et al.. Past aridity and dust drove biodiversity crises and altered pollination in the ancient gymnosperm (Gnetales). Biological Reviews, 2025, 100 (4), pp.1680-1697. 10.1111/brv.70019 . insu-05025582

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# Past aridity and dust drove biodiversity crises and altered pollination in the ancient gymnosperm *Ephedra* (Gnetales)

Natasha Barbolini<sup>1,2,*</sup> ●, Niels Meijer<sup>3</sup>, Carina Hoorn<sup>4</sup>, Guillaume Dupont-Nivet<sup>5,6</sup>, Fang Han<sup>7</sup>, Ashley Krüger<sup>8</sup>, Qin Yuan<sup>9,10</sup>, Alexander Rohrmann<sup>11</sup>, Kristina Bolinder<sup>1</sup> and Catarina Rydin<sup>1</sup>

## ABSTRACT

The long-term effects of present-day climate change on pollination are unquantified. However, distinguishing climatic drivers of ancient changes in pollination could provide valuable insights into biotic responses to near-future climate states. Herein, we show that pollination in a group of gymnosperm shrubs (*Ephedra* L., Gnetales) was irrevocably altered by the Cenozoic expansion of drylands on two different continents. In Asia, increased continentality during the mid-Eocene drove aridification and strong, dust-carrying storms that promoted a shift to prevailing wind pollination in the core clade of *Ephedra*. Surface uplift in the North American interior together with global cooling caused the expansion of aeolian deposition and placed similar evolutionary pressures on ephedras there, beginning in the latest Eocene and continuing across the Eocene–Oligocene transition (EOT). These climatic changes fundamentally altered the abundance and evolution of this ancient plant lineage on both continents and determined pollination mechanisms in the core clade of *Ephedra* today. Based on fossil evidence, this review demonstrates how climate change may have major and permanent impacts on plant–pollinator networks, as well as demonstrates possible evolutionary consequences of near-future climate scenarios for which we have no modern analogue.

Key words: pollen, *Ephedripites*, ephedroid, entomophily, anemophily, climate change, loess, Eocene, Oligocene, fossil.

## CONTENTS

<table><tr><td>I. Introduction</td><td>2</td></tr></table>

<footnote n="1"><sup>1</sup>Department of Ecology, Environment and Plant Sciences and Bolin Centre for Climate Research, Stockholm University, Stockholm SE-106 91, Sweden</footnote>

<footnote n="2"><sup>2</sup>Department of Biological Sciences, University of Bergen and Bjerknes Centre for Climate Research, Bergen 5020, Norway</footnote>

<footnote n="3"><sup>3</sup>Senckenberg Biodiversity and Climate Research Centre (SBiK-F), Senckenberganlage 25, Frankfurt am Main 60325, Germany</footnote>

<footnote n="4"><sup>4</sup>Department of Ecosystem and Landscape Dynamics, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam 1098 XH, The Netherlands</footnote>

<footnote n="5"><sup>5</sup>Geosciences Rennes UMR-CNRS, Université de Rennes, Rennes 35042, France</footnote>

<footnote n="6"><sup>6</sup>Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam, Germany</footnote>

<footnote n="7"><sup>7</sup>School of Earth Sciences, East China University of Technology, Nanchang, Jiangxi 330013, China</footnote>

<footnote n="8"><sup>8</sup>Department of Palaeobiology, Swedish Museum of Natural History, Box 50007, Stockholm SE-104 05, Sweden</footnote>

<footnote n="9"><sup>9</sup>Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, People's Republic of China</footnote>

<footnote n="10"><sup>10</sup>Qinghai Provincial Key Laboratory of Geology and Environment of Salt Lakes, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, People's Republic of China</footnote>

<footnote n="11"><sup>11</sup>Institute of Geological Sciences, Freie Universität Berlin, Berlin 12249, Germany</footnote>

<footnote>* Author for correspondence (Tel.: +46 816 20 00; E-mail: natasha.barbolini@su.se).</footnote>
<table><tr><td>II. Features of insect- versus wind-pollinated ephedroid pollen</td><td>3</td></tr><tr><td>III. Methods</td><td>6</td></tr><tr><td>IV. Fossil documentation of ephedroid pollen in the northern hemisphere through time</td><td>7</td></tr><tr><td>(1) North American ephedroid pollen</td><td>7</td></tr><tr><td>(2) Central Asian ephedroid pollen</td><td>8</td></tr><tr><td>V. Ephedroid pollen diversity, pollination and climate change</td><td>9</td></tr><tr><td>(1) Climatic influences on North American ephedroids in the early-mid Cenozoic</td><td>10</td></tr><tr><td>(2) Climatic influences on Central Asian ephedroids in the early-mid Cenozoic</td><td>10</td></tr><tr><td>(3) Climate change drives shifts in pollination syndrome</td><td>10</td></tr><tr><td>(4) Future perspectives</td><td>12</td></tr><tr><td>VI. Conclusions</td><td>12</td></tr><tr><td>VII. Acknowledgements</td><td>13</td></tr><tr><td>VIII. References</td><td>13</td></tr><tr><td>IX. Supporting information</td><td>18</td></tr></table>

# I. INTRODUCTION

Unprecedented global climate change has occurred during the Anthropocene, affecting ecosystems, human infrastructure, agriculture, and pollination (IPCC, 2023). Pollination is an essential service without which all major terrestrial ecosystems would not survive, but our knowledge and response actions have not kept up with the threats it faces (Potts & Imperatriz-Fonseca et al., 2016). Climate-driven shifts in phe-nology and ranges are causing mismatches between many plants and their pollinators, with too few studies available to draw broad conclusions on the consequences for plant-pollinator networks (Settele, Bishop & Potts, 2016).

Reconstructing pollination systems of the past can provide valuable information for understanding how plant-pollinator networks could respond to climate change, particularly since Earth's climate state is rapidly moving to atmospheric carbon dioxide concentrations not seen for ~15 million years (Ma), and perhaps as much as ~50 Ma (Burke et al., 2018; Steinthors-dottir et al., 2021). An additional advantage of studies on the pre-human past is that it is difficult to disentangle contemporary climate change effects on pollination from other interacting, human-caused drivers such as land degradation and pesticides (Potts & Ngo et al., 2016; Knight et al., 2018). While no palaeo-climate can be a perfect equivalent for future climate scenarios, deep-time fossil archives are playing a crucial role in under-standing the sensitivity of Earth systems to global change (Burke et al., 2018; Steinthorsdottir et al., 2021).

Fossils of *Ephedra* (Gnetales) are preserved in sedimentary archives around the world, representing a group of ancient gymnosperm shrubs with a very long history (at least ~125 Ma) that still exist today (summarised in Friis, Crane & Pedersen, 2011; also see Ickert-Bond & Renner, 2016; Rydin & Hoorn, 2016). They are remarkably resilient, hav-ing survived at least one global mass extinction, as well as numerous other hyperthermal and cooling events. Ecological experimentation and observations, and aerodynamic studies indicate that at least two distinctly different pollination mech-anisms occur today in *Ephedra*, and evolutionary shift(s) in pollination are hypothesised to have taken place in the past

(Rydin & Bolinder, 2015; Bolinder et al., 2016a). This makes these plants with a near-global distribution an ideal group for studying how and why plant-pollinator networks could change in response to future climate scenarios, for which we have no modern analogue.

The oldest unambiguous ephedroid fossils belonging to the Gnetales, as the order is defined today, are mostly from low palaeolatitudes where they appear to have been abundant in the Early Cretaceous. This is documented by an increasing number of macrofossil discoveries as well as microfossil evidence (for references see online Supporting Information, Table S1). Pre-Cretaceous ephedroids have been reported in the literature (see for example Wang, 2004) but the exact relationship of these intriguing fossils to the present-day Gnetales remains controversial [see Coiro et al. (2022) for further discussion]. Accordingly, here we focus on the Cretaceous and Cenozoic record of ephedroids, mostly comprising microfossil data (Fig. 1), which shows that ancient climate change and/or competition with early angio-sperms may have pushed ephedroids to refugia at higher palaeolatitudes from the mid-Cretaceous onwards. Ephedroid pollen has been widely used as a climate proxy to indi-cate a dry palaeoenvironment (e.g. Sun & Wang, 2005), but precise reasons for the repeated and globally occurring peaks and crashes in ephedroid diversity and/or abundance (Fig. 1) have never been rigorously assessed, hindering palaeoclimate reconstructions and our understanding of past pollination syndromes in ephedroids.

Surprisingly, ephedroids seem to have been relatively unaffected by the enormous ecological upheavals that took place during the Cretaceous–Paleogene (K–Pg) mass extinc-tion 66 million years ago (Fig. 1). Our initial overview instead indicates major fluctuations in the presence of fossil ephedroid pollen before the K–Pg boundary (in low palaeolati-tudes and the Southern Hemisphere), and long after the K–Pg boundary in the Northern Hemisphere (Fig. 1). Both Central Asia and North America show major changes in ephedroid pollen types during the late Paleogene (Tables S2 and S3). Based on this evidence, here we review and explore records of ephedroids in these regions from the
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** (A) Global distribution of ephedroids through time based on occurrence of dispersed ephedroid pollen in sediments from the Early Cretaceous to the present. Plotted points each represent a reported percentage of ephedroid pollen, or absence thereof, from a fossil locality described in a palynoflora or palynological assemblage. (B) The 207 underlying data points (Table S1) are relatively evenly spread over the investigated time-space. (C) Scatter plot of record co-ordinates (black circles) for visual assessment of clustering compared with randomly simulated points at the same density (red points). (D) Histogram plot of number of records through time. In C and D, the peaks of ephedroid abundance identified in A are represented by coloured stars, illustrating that these peaks are not influenced by underlying spatio-temporal biases in the data set. The stars are coloured in the respective colours of the chronostratigraphic periods shown in A and the sizes of stars span the records that generate that particular peak, with no implication on peak size.</figcaption></figure>

Cretaceous to the present, providing the opportunity to test the hypothesis that drastic climate changes, from greenhouse to icehouse states, may have driven biodiversity crises and shifts in pollination syndrome. We assess the role that climate and pollination played in the survival of the family to the present and the significance of our findings for predictions of short- and long-term consequences for plant-pollinator networks under a changing climate.

## II. FEATURES OF INSECT-VERSUS WIND-POLLINATED EPHEDROID POLLEN

Almost all extant *Ephedra* species are wind-pollinated, and have morphological adaptations of pollen to enhance the process aerodynamically, as well as adaptations related to pollen

reception. Wind-pollinated ephedras create an air flow pattern around the female cone that enhances capture of specific pollen, directing it towards the pollination drops (Fig. 2A, B; Niklas, Buchmann & Kerchner, 1986; Niklas & Kerchner, 1986; Niklas & Buchmann, 1987; Buchmann, O'Rourke & Niklas, 1989; Bolinder, Niklas & Rydin, 2015; Niklas, 2015). These specialised properties for pollen reception are absent in the sole living insect-pollinated species of *Ephedra*, *E. foeminea* Forssk. (Fig. 2C; Bolinder *et al.*, 2015). One reason for this difference among species in aerodynamic properties is the orientation of the pollen-receptive surfaces in relation to the direction of the airflow (Niklas, 1985; Bolinder *et al.*, 2015); female cones of wind-pollinated species of *Ephedra* are typically tilted with respect to gravity (Fig. 2D, E), whereas those of the insect-pollinated *E. foeminea* are upright (Fig. 2F). In addition, there are other differences between insect-pollinated and wind-pollinated ephedran species: the
<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Aerodynamics and pollen reception in female ephedroid cones. (A–C) Computer simulations of pollen grain (shown in orange) aerodynamics around ovules with pollination drops (shown in green) of three extant species *Ephedra trifurca* Torr. ex S. Wats. (A), *E. nevadensis* S.Wats. (B), and *E. foeminea* Forssk. (C) in lateral view (modified after Niklas & Buchmann, 1987; Bolinder *et al.*, 2015; Niklas, 2015). Airflow direction is from left to right in all panels. (D–F) Female cones of *Ephedra*. Wind-pollinated species of *Ephedra*, such as *E. distachya* L. (D, E) often have a tilted orientation on the plant and they create an airflow pattern that enhances their capacity to capture pollen of the correct size. The female cones of the insect-pollinated *E. foeminea* (F) lack these features, and its female cones are upright, born on bent pedicels (F). Photographs: Kristina Bolinder.</figcaption></figure>

insect-pollinated *E. foeminea* has morphologically bisexual male cones that attract pollinators using pollination drops; and the derived type of ephedroid pollen (see below) is known only in wind-pollinated species. Morphological differentiation in modern and extinct *Ephedra* is generally low (e.g. Rydin, Pedersen & Friis, 2004; Rydin, Khodabandeh & Endress, 2010), yet these examples demonstrate that small morphological differences can have substantial functional consequences. Unfortunately, variation in female cone morphology is challenging to observe in the fossil record: while a diverse record of ephedroid plant macrofossil remains (as well as pollen) have been reported from the Early Cretaceous, the fossil record of *Ephedra* for the Late Cretaceous and Cenozoic is based solely on pollen (Rydin & Hoorn, 2016). Accordingly, herein we focus on ephedroid pollen.

Ephedroid pollen (extant and fossil) can be classified into two types: ancestral and derived morphotypes (Bolinder *et al.*, 2016b; Han *et al.*, 2016). The ancestral pollen type, known at least since the Early Cretaceous and identified in *situ* in ephedroid seeds from this epoch (Rydin *et al.*, 2004), has numerous plicae interspersed with unbranched pseudosulci (Fig. 3: type I). The derived pollen type, not known in

the fossil record until the Late Cretaceous (Rydin *et al.*, 2021), has on average fewer plicae than the ancestral type and occurs in two forms, either with first-order side branches on the pseudosulci (Fig. 3: type II) or with first- and second-order side branches (Fig. 3: type III). On this basis, the palynological form genus *Ephedripites* is divided into the two subgenera *Ephedripites* subgen. *Ephedripites* and *Ephedripites* subgen. *Distachyapites* (following Han *et al.*, 2016), which correspond to the ancestral and derived types respectively (Bolinder *et al.*, 2016b).

Pollen morphology, particularly pseudosulcus branching, is linked to pollination syndrome in living *Ephedra*. The derived pollen type is, as far as is known, produced exclusively by wind-pollinated plants (Bolinder *et al.*, 2015; Niklas, 2015). Bolinder *et al.* (2015) showed that pseudosulcus branching facilitates wind pollination in several ways, which together contribute to an ability to remain airborne for longer. The ultrastructure of the pollen wall also affects its aerodynamic properties and may be linked to pollination syndrome. The insect-pollinated *E. foeminea* produces the ancestral type of pollen with a small infratectum compared to pollen of the derived type (Bolinder *et al.*, 2015). This is
<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Morphology and pseudosulcus branching in *Ephedra* pollen. (1) Illustrations of the ancestral (type I) and derived (type II: first-order branching; type III: second-order branching) patterns, which are present in both living and fossil grains (drawn after an original in Bolinder *et al.*, 2016b). (2) Light microscope (LM) and (3) scanning electron microscope (SEM) images of *Ephedripites* (fossil *Ephedra* pollen) from the Eocene of Central Asia; 2 & 3 (I.), *E. lanceolatus* Zhu & Wu (1985), 2 & 3 (II.), *E. fusiformis* Habib (1970), 2 & 3 (III.), *E. fushunensis* Sung & Tsao (1978). LM and SEM photos of each morphospecies depict different pollen grains. LM photos: Natasha Barbolini; SEM photos: Fang Han.</figcaption></figure>

likely another reason why these grains stay airborne for shorter periods compared to those of the sympatric wind-pollinated species *E. distachya* L. (Bolinder *et al.*, 2016a). The ancestral pollen type in *E. foeminea* was also shown to have a tendency to form clumps, which further inhibits their ability to remain airborne (Bolinder *et al.*, 2015, 2016a).

Ancestral *Ephedripites* pollen grains from the Early to mid-Cretaceous possess a similar ultrastructure to that of *E. foeminea* pollen, with a thick tectum and small infratectum (Trevisan, 1980; Bolinder *et al.*, 2015), suggesting they may have been insect-pollinated. This assumption is supported by observations of ovular support and strong thickening of the micropylar tube both in fossils and living species (e.g. Rydin & Friis, 2010; Rydin *et al.*, 2010). These traits could protect the micropylar tube from bending or breakage when supporting the weight of visiting insects. Strong thickening of the micropylar tube is retained in several modern species of *Ephedra* that produce pollen of the ancestral type (e.g. *E. foeminea* and *E. aphylla* Forssk.) but has been lost in modern wind-pollinated species of *Ephedra* with the derived type of pollen, such as *E. distachya* (Rydin *et al.*, 2010).

At least one presumed wind-pollinated species [the North American *E. trifurca* Torrey ex S. Watson (Niklas *et al.*, 1986; Niklas & Kerchner, 1986; Buchmann *et al.*, 1989)] produces the ancestral pollen type, thus obscuring any correlation between pollen type and pollination syndrome, at least for the ancestral pollen type. Interestingly however, Niklas & Buchmann (1987) describe *E. trifurca* as "more of an aerodynamic generalist" compared to the sympatric wind-pollinated *E. nevadensis* S.Watson with its derived type of pollen. Similar claims

of a generalist pollination system utilising both abiotic and biotic vectors for pollen transfer have been made for two Mediterranean species with the ancestral type of pollen, *E. aphylla* (Meeuse *et al.*, 1990) and *E. fragilis* Desf. (Celedón-Neghme, Santamaría & González-Teuber, 2016), and investigations of additional species are warranted. While the presence of current or former wind-pollinated species that produce the ancestral type of pollen cannot be excluded, current knowledge suggests that the ancestral ephedran pollen type is and was mostly linked to insect pollination, although sometimes in combination with abiotic pollen transfer in an ambophilous system.

One argument sometimes used to suggest that Cretaceous ephedras were wind-pollinated, rather than insect-pollinated, is the comparatively strong presence of ephedroid pollen in many fossil archives. The extant wind-pollinated species *E. distachya* generally produces much more pollen than the insect-pollinated *E. foeminea* (Bolinder *et al.*, 2015, 2016b; Hofmann, Roberts & Seyfullah, 2022). However, the extinct entomophilous conifer family Cheirolepidiaceae (Pocock, Vasanthy & Venkatachala, 1990; Krassilov, Zherikhin & Rasnitsyn, 1997; Krassilov, Rasnitsyn & Afonin, 2007; Labandeira, Kvaček & Mostovski, 2007; Ren *et al.*, 2009) exemplifies that such a pattern is not universal. The Cheirolepidiaceae produced distinctive pollen (*Classopollis* Pflug) that is at least as abundant or more so than that of known abiotically pollinated plants in many deposits globally (e.g. Archangelsky & Gamerro, 1967; Vakhrameev, 1981; Wang, Mosbrugger & Zhang, 2005; Barreda *et al.*, 2012; Tosolini *et al.*, 2015; Zhang *et al.*, 2019). Both cheirolepidiaceous and gnetalean pollen have been found in the gut contents of
several Mesozoic insect lineages (Krassilov *et al.*, 1997, 2007; Labandeira *et al.*, 2007), and must have served as a nutritional source and/or pollination reward.

Thus, based on these data and observations of fossil and living species, it has been suggested that insect pollination was more common in *Ephedra* in the past than it is today, perhaps even originally the dominant mode of pollination in the genus (Bolinder *et al.*, 2015, 2016b). A variety of new (derived) ephedroid pollen types (see Fig. 3) not known before the Turonian–Coniacian boundary of the Late Cretaceous (Steeves & Barghoorn, 1959; Rydin *et al.*, 2021) became common in the Paleogene (from *ca.* 58 Ma) and largely replace the ancestral pollen type in many Cenozoic strata (Han *et al.*, 2016). The novel pollen type shares the characters of wind-pollinated *Ephedra* species today, and it was thus hypothesised that an evolutionary shift to wind pollination occurred relatively rapidly in *Ephedra* (Bolinder *et al.*, 2015, 2016a; Hofmann *et al.*, 2022). In these studies, the catastrophic asteroid impact at the K–Pg boundary was tentatively suggested to have caused this evolutionary transition (e.g. Bolinder *et al.*, 2016a) but a rigorous temporal and causal framework for this hypothesis was not established. Therefore, herein we show that Cenozoic climate changes appear to have played a primary role in driving pollination shifts in the ephedran lineage.

### III. METHODS

To obtain an initial overview of ephedran abundance changes through time, a database of the global distribution of *Ephedripites* (i.e. pollen of the genus *Ephedra*) from the Early Cretaceous to the present was assembled, following the approach of Crane & Lidgard (1989) (Table S1). In this data set, pollen was not separated into morphospecies (i.e. species based solely on morphology), since many previously published studies did not provide this information. While this data set cannot therefore provide information about pollination changes in ephedras through time, it can be used to identify overarching patterns and particular geographical areas and time periods of interest, which we could then focus on using a smaller but more detailed data set (see Sections IV and V). The data were made continuous by a linear interpolation using the Akima package, and a 3D plot (Fig. 1A) was constructed using the *persp* function, both in R v. 4.3.1 (R Development Core Team, 2023).

To test for spatial and temporal biases, we used the *dynamicSDM* package for R (Dobson *et al.*, 2023) to perform a chi-squared test (Greenwood & Nikulin, 1996) to assess temporal sampling bias, and a *t*-test following the nearest neighbour index (Clark & Evans, 1954) to assess spatial bias (see footnote to Table S1 for results). While the global fossil ephedroid record is biased in space and time, a scatter plot of record co-ordinates for visual assessment of clustering (Fig. 1C) and a histogram plot of record frequency through time (Fig. 1D) show that the record is biased towards the late

Neogene and to continental landmasses (accounting for changing palaeogeography through time), as expected for fossil records of a land plant. Considering that all palaeontological data sets contain varying degrees of taphonomic and collecting bias, we sought to identify whether the abundance peaks in Fig. 1A are influenced by the inherent bias of the fossil record. Plotting these abundance peaks (represented by stars in Fig. 1B–D) onto the spatiotemporal spread of data points, it is clear that these peaks are not biased by their location in time (Fig. 1B), space (Fig. 1C) or the number of records collected (Fig. 1D).

This overview of repeated rises and crashes in global ephedroid abundance through time (Fig. 1B) was then used to focus attention on particular areas of interest (in time and space), where we can use more data, often with better and/or independent age control and better possibilities to identify the grains to morphospecies. Using these criteria, we assembled an Early Cretaceous–Holocene compilation of ephedroid pollen (Tables S2 and S3) restricted to the genus *Ephedripites* Bolkhovitina (1953) ex Potonié (1958) emend. Krutzsch (1961) and separated into morphospecies where possible (following Han *et al.*, 2016) or pollen types (Fig. 3). The genus *Ephedripites* has sometimes been called *Ephedra* or *Equisetosporites* by various authors. When the latter name was used in a publication, identification was confirmed visually as many morphospecies of *Equisetosporites* are not ephedroid pollen. Similarly, some studies did not distinguish to species or type of *Ephedripites*, and in such cases identification was conducted based on photographs and/or descriptive text wherever possible.

Published data from North America (Table S2) and Central Asia (Table S3) were compiled together with an updated and expanded record from the well-dated and time-extensive Xining Basin in Central Asia (N. Barbolini, H. van den Hil, C. Hoorn, A. Woutersen, N. Meijer, G. Dupont-Nivet, F. Han, A. Rohrmann & C. Rydin, in preparation). We used this data set to study fluctuations in diversity and relative abundance of *Ephedra* through time on both continents, and to infer pollination changes (Fig. 4). Two main limitations exist for this data set, namely, that (i) the number of pollen morphospecies in any stratigraphic horizon almost certainly does not equal a direct count of actual plant species living at that time, and (ii) differing amounts of pollen produced by wind- versus insect-pollinated plants may introduce a bias into the interpretation of relative pollen counts. To mitigate the first limitation, we assume that a relative change in pollen abundance broadly corresponds to an overall change in regional plant diversity over a longer period of time (i.e. multiple seasons). To reduce possible effects of the second limitation, we use both proportions and raw counts when comparing the fossil pollen record of ancestral (likely insect-pollinated or mixed pollination strategies) versus derived (likely wind-pollinated) ephedroid pollen.

For the Asian data, included samples were counted by only two authors (F. Han and N. Barbolini) and followed the same method, controlling for raw counts and using the morphospecies figured in Han *et al.* (2016). We thus considered it appropriate to link relative abundances with climatic events. The North
<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Location of the study areas in North America and Central Asia. (A, B) Study sites (letters) detailed in Tables S2 and S3. Loess plateau reconstructions are derived from Fan *et al.* (2020) and Meijer *et al.* (2021). The palaeogeographic reconstruction (at 40 Ma) is from Poblete *et al.* (2021); the data and map were downloaded from the Paleoenvironment map website (https://map.paleoenvironment.eu) on 08 June 2022, using the following parameters: reconstruction time: 40 Ma, Indo-Asia tectonic model: Double Collision Greater India Basin, palaeogeography: Turgai Strait open. Colours indicate meters above sea level (m a.s.l.). Note that study sites range in age from Cretaceous to Oligocene.</figcaption></figure>

American data were derived from published studies by multiple authors, generating more uncertainty in how these data can be compared. Accordingly, for the North American data set we primarily use the Cretaceous absence and Cenozoic appearance of the derived type of pollen and of second-order pseudosulcus branching (which are confirmed by the same pattern globally) rather than the relative abundances of raw counts to infer the onset of dust storms and aridity in the middle-late Eocene of North America. Furthermore, based on all records, it is clear that the first presence of the derived type globally is within the Cretaceous Raritan Formation in North America, whereas the ancestral type is clearly older.

## IV. FOSSIL DOCUMENTATION OF EPHEDROID POLLEN IN THE NORTHERN HEMISPHERE THROUGH TIME

### (1) North American ephedroid pollen

Pollen records from the USA and Canada show that the ancestral type of *Ephedripites* (unbranched pseudosulci; Fig. 3: type I) was already common by the late Early

Cretaceous. It is present in multiple localities across western North America and often identified as "*Equisetosporites ovatus*" in the literature (Table S2). The ancestral pollen type is commonly present together with *Gnetaceae/pollenites* F. Thiergart (1938), which is restricted to the Late Cretaceous—Paleocene; we agree with Frederiksen (1980) that the few grains recovered from the late Eocene of Alabama are almost certainly reworked (Table S2). The derived (branched pseudosulci) pollen type first appears in the early Late Cretaceous (Turonian; Steeves & Barghoorn, 1959; locality c of Fig. 4A), but remains rare in North America until the middle Eocene (dating not precise enough to refine this to either the Lutetian or the Bartonian; Table S2). The derived type with first- and second-order psuedosulci branching (Fig. 3: type III) appears infrequently from the middle Eocene (Lutetian) but only becomes common in the late Eocene (Bartonian) in Alabama and South Carolina, and the latest Eocene in Colorado (Table S2).

As the derived types of *Ephedripites* become more common, so the ancestral type becomes rarer, and during the middle-late Eocene the latter is not found in samples where the derived types are present (localities 1–o of Fig. 4A). In the late Eocene of Alabama and the late Oligocene of
South Carolina, a single ancestral species [*E. (E.) hungaricus* Nagy (1963)] is infrequently recorded (Table S2). Latest Eocene and Oligocene floras (34.1–26.9 Ma) from central and southwestern Colorado (Leopold & Zaborac-Reed, 2019) contain a single ancestral type, *E. (E.) torreyana* Steeves & Barghoorn (1959), in very low proportions of the total pollen counts (Table S2). In the late Oligocene, the derived type comprises 9% of an assemblage from western Utah, compared with 1.5% for the ancestral type (Table S2). Thus, the derived type of pollen is clearly much more abundant than the ancestral type from the middle Eocene onwards.

## (2) Central Asian ephedroid pollen

The Central Asian region comprises modern-day Mongolia, northern and western China, and northwestern (geographic) Tibet (Barbolini et al., 2020). Ephedroid pollen is reported infrequently and in low amounts from this region during the Early Cretaceous (Table S3). By the Late Cretaceous, the derived pollen types with first- and second-order branching became common and Central Asia hosted a high ephedroid diversity (>100 morphospecies) during the Late Cretaceous–Cenozoic (b in Table S3; Wang et al., 1990b; Song et al., 1999). Many new morphospecies emerged in the Eocene, particularly the derived types (Han et al., 2016), and *Ephedra* evidently formed a significant component of Central Asian vegetation for tens of millions of years (Wang et al., 1990b; Zhang & Zhan, 1991; Sun & Wang, 2005; Hoorn et al., 2012; Ivarsson, 2013; Bosboom et al., 2014; Barbolini et al., 2020). Pollen grains of all three types (I–III; Fig. 3) are present in most samples from the high-resolution Xining Basin record in northeastern Tibet (locality b in Fig. 4B), but their abundance and diversity change markedly through the late Paleocene to early Oligocene (Table S3).

In general, the ancestral type is more common in the early Eocene, spikes in the middle Eocene, and decreases in the late Eocene to become rare thereafter (localities b, d and e of Fig. 4B; Table S3). One of our Eocene samples from Xining (dated to ~39.9 Ma with an upper error limit of

40.2 Ma) contained numerous disassociated arthropod (insect/arachnid) parts, one with setae bearing trapped ephedroid pollen grains of the ancestral type (Fig. 5A, B). Note, however, that all samples underwent typical palynological processing with disaggregation, acid digestion, and centrifugation, meaning that this association may simply be taphonomic. However, this sample contained both the highest abundance and diversity of ancestral types of ephedroid pollen [i.e. pollen type I (Fig. 3) that is produced by all species known to be insect-pollinated or ambophilous (Rydin & Bolinder, 2015; Bolinder et al., 2016a,b; Meeuse et al., 1990; Celedón-Neghme et al., 2016), but possibly also some wind-pollinated species] out of all samples in the detailed Xining record (N. Barbolini, H. van den Hil, C. Hoorn, A. Woutersen, N. Meijer, G. Dupont-Nivet, F. Han, A. Rohrmann & C. Rydin, in preparation). In addition, the pollen is attached to the setae in the same way as modern pollen produced by the insect-pollinated *Ephedra foeminea* attaches to the setae of its vector (Fig. 5C; Bolinder et al., 2016a). The occurrence of the ancestral ephedroid pollen type (Fig. 3: type I) subsequently rapidly declines, concurrently with the middle-late Eocene rise in abundance of derived ephedroid pollen.

First- and second order-branched (derived) pollen (Fig. 3: types II and III) become increasingly abundant and more diverse through the Eocene up until the Eocene–Oligocene Transition (Table S3). Early Oligocene samples may contain rare pollen grains of the ancestral type along with those of the derived type but late Oligocene samples lack the ancestral type and pollen with second-order branching appears rare in the entire epoch (localities b and e–g of Fig. 4B; Table S3). The same is true for Miocene, Pliocene and Quaternary samples; pollen grains of the ancestral type are absent and of most of the derived type of pollen lacks second-order branching, although the latter is present in Miocene sediments from the Qaidam Basin (locality h of Fig. 4B; Table S3). It should be noted, however, that some studies in the literature did not distinguish between the different ephedroid morphospecies (see also Section III and Tables S2 and S3). Where possible, we reassessed the type

<figure><img src="image_7.png" /><figcaption>**Fig. 5.** Ancestral-type *Ephedra* pollen on arthropod legs. (A) Eocene (~39.9 Ma) *Ephedripites* pollen grain of the ancestral type, attached to a seta of an arthropod (sample TF P4-18). (B) Same image at lower magnification, with a grain of another ancestral ephedroid pollen type, *Steevesipollenites major* Zhang & Zhang (1991), visible to the left. (C) Modern pollen grain of ancestral-type *Ephedra foeminea* on the leg of an insect of *Sciaridae* (Bolinder et al., 2016a). Photographs A and B: Natasha Barbolini.</figcaption></figure>
more specifically, based on photographs and/or descriptions
in the original work.

V. EPHEDROID POLLEN DIVERSITY,
POLLINATION AND CLIMATE CHANGE

The global, North American, and Central Asian palynologi-
cal data sets synthesised here (Figs 1 and 6; Tables S2 and S3)
document ephedroid diversity from the Cretaceous to the
present, thus covering major climate changes over the K–
Pg boundary (66 Ma), the Middle Eocene Climatic Opti-
mum (MECO; 40 Ma) and the Eocene–Oligocene

Transition (EOT; 34 Ma). We find clear evidence of substan-
tial peaks and crashes in ephedroid diversity/abundance
over time (Fig. 1) and the Cenozoic fluctuations involve dif-
ferences in relative abundance of the various types of ephe-
droid pollen, differences that can be correlated with climate
and pollination strategy (Fig. 6).

The presence of ephedroids in the Northern Hemisphere
during the Early Cretaceous is clearly documented based
on macrofossil as well as microfossil evidence (summarised,
e.g. by Friis *et al.*, 2011) but most records are from low
palaeolatitudes where only pollen of the ancestral
unbranched type is documented. At higher palaeolatitudes,
presence of ephedroid pollen in rocks/sediments increases
during the Late Cretaceous but is still mostly of the ancestral

<figure><img src="image_8.png" /></figure>

**Fig. 6.** Evolution of ephedroid pollen types (depicted as shaded bars) in North America and Central Asia in relation to global temperatures (represented by the benthic foraminifera oxygen record of Westerhold *et al.* (2020) and Eocene–Oligocene aridity changes (represented by Proto-Paratethys sea incursions; Kaya *et al.*, 2019) in Central Asia and floristic turnover in Colorado (Leopold & Zaborac-Reed, 2019). Future projections for global temperature in the year 2300 (Palmer, Harris & Gregory, 2018) are indicated by three representative concentration pathways (RCP) scenarios (light blue, dark blue, and orange circles) in comparison to today (green circle). UNB = unbranched (ancestral, type I) pollen grains; 1ST = pollen grains with first-order branching of the pseudosulci (derived, type II); 2ND = pollen grains with first- and second-order branching of the pseudosulci (derived, type III). Darker shading indicates increased abundance of that pollen type. Pollen abundances were compiled using references from Tables S2 and S3 as well as Jarzen *et al.* (2010), Loera *et al.*, (2012), Garcia *et al.* (2016) and Han *et al.* (2016). Question marks indicate time periods of uncertainty. Modern biogeography of *Ephedra* species is from Bolinder *et al.* (2016b). EOT = Eocene–Oligocene Transition; MECO = Middle Eocene Climatic Optimum. Chronostratigraphy is from Cohen *et al.* (2013); updated to v2022/10).
unbranched type. The eastern USA holds the earliest well-documented record of the derived pollen of *Ephedripites* (Rydin *et al.*, 2021). It is of the first-order branching type (Fig. 3: type II), and was discovered by Steeves & Barghoorn (1959) from the upper part of the Raritan Formation [Zone V of Doyle & Robbins (1977) and personal communication with J.A. Doyle in 2021], which is of latest Turonian or Coniacian age (Massoni, Couvreur & Sauquet, 2015). Reports of the derived pollen type in older strata, for example of *Ephedripites fusiformis* from Cenomanian deep-sea outcrops in the North Atlantic (Habib, 1970), exist but are extremely rare and need further research. In Asia, all three major types of ephedroid pollen (Fig. 3) are present by the latter Late Cretaceous (Fig. 6) and records of ephedroid pollen are abundant, with the ancestral unbranched forms such as *Ephedripites*, *Gnetaceae/pollenites*, and *Sleevesipollenites* the most common (as exemplified from the Xining Basin; Han *et al.*, 2016).

In general, the ephedroid pollen record in North America and Central Asia follows the same trend; the ancestral type of pollen is dominant in the Cretaceous and derived pollen types become increasingly common in the Cenozoic (Fig. 6; Tables S2 and S3). However, while the derived first- and second-order branched types seem to be equally prevalent in Central Asia, there is a transition from dominance of the first-order branched type in the Middle Eocene (?Lutetian/Bartonian) to co-dominance of both derived types at the Eocene–Oligocene Transition in North America (Fig. 6).

## (1) Climatic influences on North American ephedroids in the early-mid Cenozoic

To understand regional patterns of climate change and biodiversity change it is important to compare well-dated records with ephedroid morphospecies-level pollen records from several localities (Fig. 4). Such localities with good age control are rare (Barbolini *et al.*, 2020), but are available for Eocene Central Asian basins such as the Xining Basin (see Section V.3 and Table S3). The poorer resolution for records in North America for localities containing abundant ephedroid pollen (Table S2) makes it more difficult to identify precisely which climatic drivers in that region were responsible for the increase in the Eocene of the derived first-order branched pollen type. If this increase took place in the Bartonian, it may have been driven by reconfiguration of the hydrological cycle and atmospheric circulation after the MECO (Mulch *et al.*, 2015; Methner *et al.*, 2016). Alternatively, changing topography due to the southward growth of the North American Cordillera from 43 to 37 Ma (Mix *et al.*, 2011; Chamberlain *et al.*, 2012) resulted in drying and dust deposition in the central Cordillera (Fan *et al.*, 2020). This atmospheric reconfiguration would have favoured the first-order branched ephedroid pollen type presumed to be dispersed by wind, and thus could explain their increased abundance during the middle Eocene. From the latest Eocene, the second-order branched type becomes the dominant form found while the first-order branched type remains common (Fig. 6). By contrast, the ancestral (unbranched)

pollen type is rare in these deposits, with only two species recorded over the late Eocene to late Oligocene (Fig. 6; Table S2).

The change to second-order branched type predominating over the ancestral (unbranched) pollen type is coeval with the eastward expansion of a loess plateau in the western US driven by global cooling culminating in the EOT (Fig. 4A; Fan *et al.*, 2020). Derived pollen remained dominant through the Oligocene in the western US (Table S2), during which the Chuska erg (a dune field of aeolian dust and sand in northwestern New Mexico and Arizona) continued to supply substantial amounts of airborne dust to the western US interior, until approximately 26 Ma (Cather *et al.*, 2008; Cather, Chapin & Kelley, 2012). A substantial increase in aridity over the Eocene–Oligocene Transition reflected by floristic turnover (Leopold & Zaborac-Reed, 2019), and an increase in the ratio of Pacific Ocean-derived winter precipitation relative to Gulf of Mexico-derived summer precipitation (Fan *et al.*, 2020) likely also favoured the derived pollen types in North America.

## (2) Climatic influences on Central Asian ephedroids in the early-mid Cenozoic

The onset of dust deposition and increases in aridity and winter precipitation also drove long-term dominance of derived (branched pseudosulci) pollen in Central Asia, although it apparently started somewhat earlier in Central Asia than in North America (Fig. 6). Another difference is that derived pollen appears to dominate Central Asian environments for shorter intervals (<~1–2 million years) starting from the Late Paleocene – but does not remain dominant for longer periods until the mid-late Eocene (earliest Bartonian; Table S3). At this point there is a spike in derived, second-order branched ephedroid pollen in the Xining Basin (Table S3) which is likely coeval with a major environmental shift: the appearance of windblown dust in the sedimentary record, a change to predominant steppe-desert vegetation, and the onset of obliquity-dominated climate cyclicity which together indicate the onset of a high atmospheric pressure system driving intensified storms in the region (Bosboom *et al.*, 2014; Meijer *et al.*, 2021). As a key steppe-desert plant, ephedras then remained consistently dominant in Central Asia for much longer than previously believed (~6 million years) until the EOT (Table S3; Barbolini *et al.*, 2020). Our review shows that these ephedras belong almost exclusively to the group (s) producing derived pollen types (Table S3), that is wind-pollinated species.

## (3) Climate change drives shifts in pollination syndrome

Evidence from the fossil record and investigations of living *Ephedra* species strongly indicate that a mix of pollination strategies existed in *Ephedra* since the Early Cretaceous, and that insect pollination was more common in this group in the past than it is today. Ephedroid pollen grains with
branched pseudosulci, which as far as is known exclusively represent wind-pollinated plants, are unknown prior to the Turonian–Coniacian (Late Cretaceous). However the unbranched ancestral pollen type, which is frequently present throughout the Cretaceous, is today produced by plants with several distinct pollination syndromes, insect-pollinated plants (Bolinder et al., 2015, 2016a,b), partly insect-pollinated (ambophilous) plants (Meeuse et al., 1990; Celedón-Neghme et al., 2016), and possibly also by some wind-pollinated species (e.g. Niklas & Buchmann, 1987). Several distinct pollination syndromes are thus highly likely to have co-existed in *Ephedra* throughout the evolutionary history of the group, with insect pollination possibly being significant during the Cretaceous and earliest Cenozoic.

The absence of sufficiently well-dated sections for the early Paleocene of Central Asia (Fig. 6) makes it hard to judge precisely the effect of the K–Pg event on pollination and the biodiversity in this region. However, work conducted in North America as well as Central Asia (e.g. Wodehouse, 1933; Wang, Sun & Zhao, 1990a) found no evidence of a substantial decline in ephedroid pollen in the Northern Hemisphere in the aftermath of the K–Pg mass extinction. In fact, our review indicates the contrary, an increased occurrence of ephedroid pollen in the Northern Hemisphere that began in the latest Cretaceous and continued uninterrupted through the Paleocene (Fig. 1). In comparison, the age and palynoflora of Eocene records is better understood and particularly well-studied for Central Asia where previous work clearly identified a general trend of branched ephedroid pollen grains successively replacing unbranched grains in the middle to late Eocene (Zhu et al., 1985; Han et al., 2016; Yuan et al., 2020).

Based on current scientific knowledge, we propose that the onset of dust storms in North America and Central Asia in the late Eocene marked a turning point in climate that was responsible for a long-term sustained evolutionary shift in *Ephedra* where wind-pollinated species successively became more common and wind pollination eventually the dominant pollination syndrome, as it is in *Ephedra* today. These climatic changes presumably led to an increased fitness of wind-pollinated species and decreased fitness of insect-pollinated species, as manifested in the observed increase in the derived types of ephedroid pollen and a concurrent decrease in the ancestral type (Fig. 6). Because the morphology of ephedran ovules and pollen grains is intricately linked to their reproductive strategy (see Fig. 2 and Section II), we argue that similar climatic changes in North America and Central Asia drove similar evolutionary changes in *Ephedra* during the Eocene (although slightly separated in time). This had permanent ramifications on ephedroid lineages, with pollen types with branched pseudosulci (produced only by wind-pollinated plants) remaining dominant on both continents since the Oligocene and still today (Fig. 6).

In North America, a general increase in second-order branched pollen coincides in time with the emergence of a North American loess plateau in the latest Eocene (Figs 4A and 6; Fan et al., 2020), and loess deposition expanded from the central Rocky Mountains eastward to the Great Plains during the EOT when

the second-order branched pollen type continued to increase (Fig. 6; Table S2). Similarly, the spike in derived, second-order branched ephedroid pollen in Central Asia in the mid-Eocene is coeval with a documented major environmental shift and the likely appearance of loess (dust) as evident from studies of the Xining Basin (Bosboom et al., 2014; Meijer et al., 2021). We consider loess as a reliable palaeoproxy for dust storms on both continents, because loess is typically preserved in foreland basins (Meijer & van der Meulen, 2023). Prior to the observed onset of loess in both North America and Central Asia, extensive and continuous foreland basin deposits are preserved that do not include loess. Therefore, if there was loess before, it would have accumulated in these basins.

The onset of loess is tightly linked to atmospheric reconfigurations in the late Paleogene (Bosboom et al., 2014; Meijer et al., 2021), which may have enhanced the efficiency of wind pollination and presented an adaptive advantage for wind-pollinated ephedroids over insect-pollinated species. Intensified winter/spring monsoonal dust storms would have facilitated long-distance transport of pollen grains. Additionally, pseudosulcus branching increases the surface area of a pollen grain and reduces terminal settling velocity, improving pollen dispersal (Bolinder et al., 2015). This would have favoured plants producing derived types of pollen.

Furthermore, pseudosulci branching facilitates dehydration and subsequent rehydration of pollen grains (Bolinder et al., 2016b; Hofmann et al., 2022), which would be an advantageous feature for derived pollen types under the increasing aridity and more seasonal precipitation that took place in Central Asia after 40 Ma (Abels et al., 2011; Bosboom et al., 2014). However, this would trade off against a delay in germination of derived-type grains because pollen must rehydrate on the female structure first (Bolinder et al., 2016b). Regional cooling, aridification, and a shift towards more spring-time precipitation at ca. 37 Ma (Dupont-Nivet, Hoorn & Konert, 2008; Abels et al., 2011; Hoorn et al., 2012; Page et al., 2019) are linked with further increases in first- and second-order branched taxa across multiple Central Asian basins (Xining, Nangqian, Qaidam) (Fig. 6; Table S3). If the Eocene (wind-pollinated) derived types germinated in spring and the (insect-pollinated) ancestral type germinated in summer as today (Bolinder et al., 2016a), a shift of the rainy season to cooler months would have advantaged wind-pollinated plants by providing extended moisture during their germination period (Fig. 6).

Although wind pollination conceivably presented a distinct advantage over insect pollination when frequent dust storms and loess deposition began in the mid-late Eocene, insect-pollinated species probably co-existed with wind-pollinated species in many areas of the Northern Hemisphere at least until the Oligocene, as is the case still today in eastern Europe-western Asia. Co-existence of wind pollination and insect pollination in ephedroids is particularly strongly indicated when both ancestral and derived pollen are detected, and by findings such as our discovery of fossil pollen of the ancestral type on a fossilised insect leg in Eocene sediments (Fig. 5A, B). The ancestral type of pollen grains produced
by *E. foeminea* are today trapped by the setae of insect pollinators in exactly the same way (Fig. 5C; Bolinder *et al.*, 2016a), suggesting the existence of a similar plant–pollinator mutualism during the Eocene.

An increased frequency of dust storms may also have disrupted reproduction in insect-pollinated ephedras. Wind-pollinated *Ephedra* today control the air flow around their ovules to the extent of being able to filter out allospecific pollen grains (Fig. 1; Niklas *et al.*, 1986; Niklas & Buchmann, 1987), and presumably also dust particles (2–50 µm). Modern insect-pollinated ephedras (*E. foeminea*; Bolinder *et al.*, 2016a; Fig. 2C, F) do not control air flow around their ovules (Bolinder *et al.*, 2015), so if this was also the case in the Eocene, dust could potentially have filled the pollination drop and blocked the exserted micropylar tube, preventing pollination. Notably, the insect-pollinated *E. foeminea* today inhabits arid areas but without significant amounts of loess or windblown dust (GBIF, 2022). *Ephedra* and other Northern Hemisphere gymnosperms with upright ovules such as juni-pers and yews may have been particularly susceptible to wind-blown dust, compared to, for example, pinaceous coni-fers, which have inverted ovules. The pollinators of *Ephedra* may also have been negatively affected by increasing aridity, but unfortunately Central Asian environments were not con-ductive to the preservation of insect fossils that could allow assessment of this. In order to survive the influx of dust and possible loss of pollinators, plants may instead have repro-duced vegetatively (e.g. Land, 1913), explaining why the ancestral type of pollen did not immediately disappear as dust storms began (Fig. 6). Ultimately though, reliance on self-propagation would have decreased plant fitness, which could explain the long-term decline of the ancestral pollen type in the late Eocene, and the eventual dominance of wind pollination we see in *Ephedra* today.

## (4) Future perspectives

The Gnetales, to which *Ephedra* belong, have long been suggested to be an ancient plant group (e.g. Arber & Parkin, 1908), but fossil documentation of this group was sparse and poorly understood until relatively recently (Crane, 1996). A wealth of Early Cretaceous macrofossil evidence has been discovered in recent decades, and studies indicate that several innovations can likely explain how *Ephedra* has escaped extinction despite repeated diversity crises, among them a probable evolution of frost tolerance during the Cenozoic (K. Bolinder, A. Humphreys & C. Rydin, unpublished data), as well as the novelties and adaptations related to pollen structure and pollination discussed herein. It is now clear that ephedroids did not again become common in the equatorial region after the mid-Cretaceous (Fig. 1; Crane & Lidgard, 1989) but several key factors and events in their long evolutionary history remain unclear and need further research.

One open question is why ephedroids are today confined to harsh environments such as steppes and deserts. They were clearly abundant in the equatorial region in the Early Cretaceous (Fig. 1) but never again comprised a substantial

element of low (palaeo-)latitude vegetation after a crash in the mid-Cretaceous. Speculatively, they may have been unable to compete successfully with angiosperms, which were rapidly diversifying at that time (e.g. shown by palynological data in Crane & Lidgard, 1989). This should be studied further in the future, as should reasons for the apparent huge rise and fall of ephedroids in the Southern Hemisphere during the Late Cretaceous (Fig. 1).

The phylogeny of *Ephedra* remains unresolved. Despite a remarkable morphological stasis of ephedras since the Early Cretaceous (e.g. Rydin *et al.*, 2004, 2006a; Rydin, Wu & Friis, 2006b), morphological, anatomical and histological work on female reproductive structures has indicated that the Cretaceous species are distantly related, extinct sister lineages to a much younger living clade (Rydin *et al.*, 2010). Later work on pollen morphology tentatively suggested otherwise, that is that the living clade may be from the mid-Cretaceous (Bolinder *et al.*, 2016b), but further clarification is needed (see Rydin *et al.*, 2021). The phylogeny and age of extant *Ephedra* has not been satisfactorily resolved despite extensive work based on genomic data (Rydin *et al.*, 2021; R. Blokzijl, N. Wikström, L. Thilén & C. Rydin, in preparation); in particular, the deepest divergences in *Ephedra* are unclear and additional analyses, preferably based on genomic data, are needed. Nevertheless, there is some agreement between earlier studies based on molecular data (e.g. Huang & Price, 2003; Ickert-Bond, Rydin & Renner, 2009; Loera, Sosa & Ickert-Bond, 2012) and our results based on microfossil data. For example, we show here that the appearance of derived (branched) ephedroid pollen was likely the result of similar evolutionary pressures in Asia and North America, rather than a shared evolutionary history, and that the second-order derived pollen type appears earlier in Asia than in North America, which is consistent with results of phylogenetic analyses (e.g. Rydin *et al.*, 2004, 2021; Ickert-Bond *et al.*, 2009; Rydin & Korall, 2009).

Because the post-Early Cretaceous history of *Ephedra* is so far only directly documented from microfossils, additional studies of ephedroid pollen and investigations of what it can and cannot tell us about the ecology of the plant that produced it are of highest relevance. A key question is whether fossil pollen preserves decisive information on pollination biology. Current knowledge strongly suggests that the derived pollen type is produced exclusively by wind-pollinated plants, whereas the ancestral pollen type may be linked to several pollination syndromes. Ecological field studies of additional extant species and further studies of pollen wall properties and terminal settling velocity of extant and fossil pollen grains may provide clarity on this.

## VI. CONCLUSIONS

(1) Ephedroids are ancient survivors that have successfully endured ever-increasing competition from diversifying angiosperms and periods of severe stress caused by abiotic
factors such as the end-Cretaceous extraterrestrial impact and the dramatic change from a greenhouse world to an icehouse world in the Oligocene. They have constituted an important element in the vegetation at least until the earliest Oligocene, for example in pre-grassland open habitats of mid-palaeolatitudes of the Northern Hemisphere, and continue to do so in highly arid areas of the world.

(2) A mix of pollination strategies is suggested to have occurred in *Ephedra* at least since the mid-Late Cretaceous, probably since the Early Cretaceous. Insect pollination was more common in *Ephedra* in the Cretaceous than today. The ancestral type of *Ephedra* pollen with unbranched pseudosulci is today produced by insect-pollinated species, ambophilous species and probably also by some wind-pollinated species. The derived type of *Ephedra* pollen with branched pseudosulci, first documented from mid Late Cretaceous North American strata, became increasingly common in the early–mid Cenozoic. This pollen type is today produced exclusively by wind-pollinated plants. The trend towards wind pollination being adopted as the dominant pollination syndrome in *Ephedra*, as it is today, can likely be explained by an increased fitness of wind-pollinated species as well as decreased fitness of insect-pollinated species following early Cenozoic climatic changes.

(3) We propose that rapid changes in temperature, aridity and seasonality strongly influenced the type of ephedroid pollen detected in sedimentary archives, and likely the reproductive strategy of these ancient gymnosperms. Early Cenozoic climate changes in Asia and North America that resulted in more frequent dust storms appear to have selected for ephedroid species with the derived pollen type (i.e. wind-pollinated species) at the expense of species that produced the ancestral pollen type (i.e. species that relied entirely or partly on insects for pollen transfer and possibly also anemophilous species). Additional studies of fossil ephedroid pollen and the information on pollination syndrome it may have preserved would be highly valuable.

(4) The long-term, well-dated ephedroid microfossil record in the Xining Basin (China) enables a correlation to be detected between ephedroid pollen type and climatic changes. Similar Cenozoic climatic changes in North America and Central Asia triggered similar morphological and evolutionary responses in *Ephedra*. It is clear that grouping fossil ephedras by pollen pseudosulcus branching type has validity for understanding past climate, vegetation and ecology. Pollen pseudosulcus branching type, which is preserved in the fossil record, is an indicator of past plant ecological preferences and pollination strategies. Our results from North America mimic the patterns detected for Central Asia; climate-related fluctuations in the relative frequencies of different pollination strategies follow the same trends in these vastly separated locations.

(5) *Ephedra* may provide a precedent showing how large-scale temperature changes and reconfiguration of atmospheric systems can drive long-term changes in pollination type. Today, desertification is spreading across Asia (and other continents) at rapid rates, and major changes are

already evident in the modern East and South Asian monsoons (IPCC, 2023). Similar climatic changes had permanent ramifications for pollination biology and reproduction of *Ephedra* in the past: a valuable lesson for predictions on how plant-pollinator networks may be affected by current and future global change.

## VII. ACKNOWLEDGEMENTS

This work was supported by the Swedish Research Council (Vetenskapsrådet) grant VR 2017-03985 to C.R., the European Research Council (grant MAGIC 649081) to N.B., N. M., G.D-N. and A.R., and the Bolin Centre for Climate Research (grant RA6_2019_12) to N.B. Funding sources had no involvement in study design. We thank the Imaging Facility at Stockholm University (IFSU) for assistance with confocal microscopy, Prof. Vivi Vajda at the Swedish Museum of Natural History for access to light microscopy facilities, and Rachel Dobson at Leeds University for assistance with the *dynamicSDM* package.

## VIII. REFERENCES

*References identified with an asterisk (*) are cited only within the online Supporting Information.*

*ABELS, H. A., DUPONT-NIVET, G., XIAO, G., BOSBOOM, R. & KRIJGSMAN, W. (2011). Step-wise change of Asian interior climate preceding the Eocene–Oligocene Transition (EOT). *Palaeogeography, Palaeoclimatology, Palaeoecology* **299**, 399–412.

*ALLEY, N. F. & BROADBRIDGE, L. M. (1992). Middle Eocene palynofloras from the One Tree Hill area, St Vincent Basin, South Australia. *Alcheringa* **16**, 241–267.

*ARBER, E. A. N. & PARKIN, J. (1908). Studies on the evolution of the angiospermsangiosperms. The relationship of the angiosperms to the Gnetales. *Annals of Botany* **22**, 489–515.

*ARCHANGELSKY, S. & GAMERRO, J. C. (1967). Pollen grains found in coniferous cones from the lower Cretaceous of PPatagonia (Argentina). *Review of Palaeobotany and Palynology* **5**, 179–182.

*ASKIN, R. A. (1983). Tithonianian (uppermost Jurassic) – Barremian (Lower Cretaceous) spores, pollen and microplankton from the South Shetland Islands, Antarctica. In *Antarctic Earth Science* (eds R. L. OLIVER, P. R. JAMES and J. B. JAGO), pp. 295–297. Cambridge University Press, Cambridge.

*ASKIN, R. A. (1990). Campanian to Paleocene spore and pollen assemblages of Seymore Island, Antarctica. *Review of Palaeobotany and Palynology* **65**, 105–113.

*BALDONI, A. M. (1992). Palynology of the Lower Lefipan formation (Upper Cretaceous) of Barranca de los Perros, Chubut Province, Argentina. Part I. Cryptogam spores and gymnosperm pollen. *Palynology* **16**, 117–136.

*BALTES, N. (1965). Observatii asupra microflorei cretaceic inferioare din zona R. Bicaz. *Petrol si Gaze* **16**, 3–17.

*BARBOLINI, N., WOUTERSEN, A., DUPONT-NIVET, G., SILVESTRO, D., TARDIF, D., COSTER, P. M. C., MEIJER, N., CHANG, C., ZHANG, H.-X., LIGHT, A., RYDIN, C., KOUTSODENDRIS, A., HAN, F., ROHRMANN, A., LIU, X.-J., ET AL. (2020). Cenozoic evolution of the steppe-desert biome in Central Asia. *Science Advances* **6**, eabb8227.

*BARREDA, V. (1997). Palynomorph assemblage of the Chenque formation, late Oligocene-Miocene from Golfo San Jorge basin, Patagonia, Argentina. Part 4. Polyporate and porate pollen. *Ameghiniana* **34**, 145–154.

*BARREDA, V. D., CÚNEO, N. R., WILF, P., CURRANO, E. D., SCASSO, R. A. & BRINKHUIS, H. (2012). Cretaceous/Paleogene floral turnover in Patagonia: drop in diversity, low extinction, and a Classopollis spike. *PLoS One* **7**, e52455.

*BARREDA, V., GULER, V. & PALAZZESI, L. (2008). Late Miocene continental and marine palynological assemblages from Patagonia. *Developments in Quaternary Science* **11**, 343–350.

*BARREDA, V., PALAZZESI, L. & MARENSSI, S. (2009). Palynological record of the Paleogene Rio Leona formation (southernmost South America): Stratigraphical and paleoenvironmental implications. *Review of Palaeobotany and Palynology* **154**, 22–33.
*BATTEN, D. J. (2007). Spores and pollen from the Crato formation: biostratigraphic and palaeoenvironmental implications. In *The Crato Fossil Beds of Brazil - Window into an Ancient World* (eds D. A. MARTILL, B. BECHLY and R. F. LOVERIDGE), pp. 566-574. Cambridge University Press, Cambridge, UK.

*BEBOUT, J. W. (1977). *Palynology of the paleoeneogene golden valley formation of Western North Dakota*. PhD Thesis: Pennsylvania State University.

*BERCOVICI, A., VAJDA, V., PEARSON, D., VILLANUEVA-AMADOZ, U. & KLINE, D. (2012). Palynostratigraphy of John's nose, a new cretaceous - Paleogene boundary section in Southwestern North Dakota, USA. *Palynology* **36**, 36–47.

BOLINDER, K., HUMPHREYS, A. M., EHRLÉN, J., ALEXANDERSSON, R., ICKERT-BOND, S. M. & RYDIN, C. (2016a). From near extinction to diversification by means of a shift in pollination mechanism in the gymnosperm relic Ephedra (Ephedraceae, Gnetales). *Botanical Journal of the Linnean Society* **180**, 461–477.

BOLINDER, K., NIKLAS, K. J. & RYDIN, C. (2015). Aerodynamics and pollen ultrastructure in *Ephedra*. *American Journal of Botany* **102**, 457–470.

BOLINDER, K., NORBÄCK IVARSSON, L., HUMPHREYS, A. M., ICKERT-BOND, S. M., HAN, F., HOORN, C. & RYDIN, C. (2016b). Pollen morphology of *Ephedra* (Gnetales) and its evolutionary implications. *Grana* **55**, 24–51.

*BONNETTI, C., MALARTRE, F., HUAULT, V., CUNEY, M., BOURLANGE, S., LIU, X. & PENG, Y. (2014). Sedimentology, stratigraphy and palynological occurrences of the late Cretaceous Erlian formation, Erlian Basin, Inner Mongolia, People's Republic of China. *Cretaceous Research* **48**, 177-192.

BOSBOOM, R. E., ABELS, H. A., HOORN, C., VAN DEN BERG, B. C. J., GUO, Z. J. & DUPONT-NIVET, G. (2014). Aridification in continental Asia after the middle eocene climatic optimum (MECO). *Earth and Planetary Science Letters* **389**, 34–42.

*BOULTER, M. C. & CRAIG, D. L. (1979). A middle Oligocene pollen and spore assemblage from the Bristol channel. *Review of Palaeobotany and Palynology* **28**, 259-272.

*BRADLEY, W. H. (1931). Origin and microfossils of the oil shales of the Green River formation of Colorado and Utah. *U.S. Geological Survey Professional Paper* **168**, 1–58.

BUCHMANN, S. L., O'ROURKE, M. K. & NIKLAS, K. J. (1989). Aerodynamics of Ephedra trifurca. III. Selective pollen capture by pollination droplets/droplets. *Botanical Gazette* **150**, 122-131.

BURKE, K. D., WILLIAMS, J. W., CHANDLER, M. A., HAYWOOD, A. M., LUNT, D. J. & OTTO-BLIESNER, B. L. (2018). Pliocene and Eocene provide best analogs for near-future climates. *Proceedings of the National Academy of Sciences* **115**, 13288-13293.

*CARATINI, C., TISSOT, C., KAR, R. K., VENKATACHALA, B. S. & SARR, R. (1991). Paleocene palynoflora from Walalane borehole, Senegal. In *Palaeoecology of Africa and the Surrounding Islands* (ed. K. HEINE), pp. 123-133. A. A. Balkema, Rotterdam/Brookfield.

CATHER, S. M., CHAPIN, C. E. & KELLEY, S. A. (2012). Diachronous episodes of Cenozoic erosion in southwestern North America and their relationship to surface uplift, paleoclimate, pedodrainage, and paleoaltimetry. *Geosphere* **8**, 1177-1206.

CATHER, S. M., CONNELL, S. D., CHAMBERLIN, R. M., MCINTOSH, W. C., JONES, G. E., POTOCHNIK, A. R., LUCAS, S. G. & JOHNSON, P. S. (2008). The Chuska erg: paleogeomorphic and paleoclimatic implications of an Oligocene sand sea on the Colorado Plateau. *Geological Society of America Bulletin* **120**, 13–33.

CELEPÓN-NEGHME, C., SANTAMARÍA, L. & GONZÁLEZ-TEUBER, M. (2016). The role of pollination drops in animal pollination in the Mediterranean gymnosperm *Ephedra fragilis* (Gnetales). *Plant Ecology* **217**, 1545-1552.

CHAMBERLAIN, C. P., MIX, H. T., MULCH, A., HREN, M. T., KENT-CORSON, M. L., DAVIS, S. J., HORTON, T. W. & GRAHAM, S. A. (2012). The Cenozoic climatic and topographic evolution of the western North American Cordillera. *American Journal of Science* **312**, 213-262.

*CHUNG, C.-H. & KOH, Y.-K. (2005). Palynostratigraphic and palaeoclimatic investigations on the Miocene deposits in the Pohang area, South Korea. *Review of Palaeobotany and Palynology* **135**, 1-11.

CLARK, P. J. & EVANS, F. C. (1954). Distance to nearest neighbor as a measure of spatial relationships in populations. *Ecology* **35**, 445-453.

*COETZEE, J. A. & ROGERS, J. (1982). Palynological and lithological evidence for the Miocene palaeoenvironment in the Saldanha region (South Africa). *Palaeogeography, Palaeoclimatology, Palaeoecology* **39**, 71-85.

COHEN, K. M., FINNEY, S. C., GIBBARD, P. L. & FAN, J.-X. (2013). The ICS international chronostratigraphic chart. *Episodes Journal of International Geoscience* **36**, 199-204.

COIRO, M., ROBERTS, E. A., HOFMANN, C.-C. & SEYFULLAH, L. J. (2022). Cutting the long branches: consilience as a path to unearth the evolutionary history of Gnetales. *Frontiers in Ecology and Evolution* **10**, 1082639.

*COOKSON, I. C. (1956). Pollen grains of the *Ephedra* type in Australian Tertiary deposits. *Nature* **177**, 47-48.

CRANE, P. R. (1996). The fossil history of the Gnetales. *International Journal of Plant Sciences* **157**, S50-S57.

CRANE, P. R. & LIDGARD, S. (1989). Angiosperm diversification and paleoaltitudinal gradients in Cretaceous floristic Diversity. *Science* **246**, 675-678.

*DAVIS, O. K. & MOUTOUX, T. E. (1998). Tertiary and Quaternary vegetation history of the Great Salt Lake, Utah, USA. *Journal of Paleolimnology* **19**, 417-427.

*DEXIN, J. & ROBBINS, E. I. (2000). Quaternary palynofloras and paleoclimate of the Qaidam basin, Qinghai province, northwestern China. *Palynology* **24**, 95-112.

DOBSON, R., CHALLINOR, A. J., CHEKE, R. A., JENNINGS, S., WILLIS, S. G. & DALLIMER, M. (2023). dynamicSDM: an R package for species geographical distribution and abundance modelling at high spatiotemporal resolution. *Methods in Ecology and Evolution* **14**, 1190-1199.

DOYLE, J. A. & ROBBINS, E. I. (1977). Angiosperm pollen zonation of the continental cretaceous of the Atlantic coastal plain and its application to deep wells in the Salisbury embayment. *Palynology* **1**, 41-78.

*DUANE, A. M. (1996). Palynology of the Byers Group (Late Jurassic-Early Cretaceous) of Livingston and Snow islands, Antarctic Peninsula: its biostratigraphic and palaeoenvironmental significance. *Review of Palaeobotany and Palynology* **91**, 241-281.

*DUENAS, H. (1980). Palynology of Oligocene-Miocene strata of borehole Q-E-22, Planeta Rica, Northern Colombia. *Review of Palaeobotany and Palynology* **30**, 313-328.

DUPONT-NIVET, G., HOORN, C. & KONERT, M. (2008). Tibetan uplift prior to the Eocene-Oligocene climate transition: evidence from pollen analysis of the Xining Basin. *Geology* **36**, 987-990.

*EDET, J. J. & NYONG, E. E. (1994). Palynostratigraphy of Nkporo Shale exposures (late Campanian-Maastrichtian) on the Calabar Flank, SE Nigeria. *Review of Palaeobotany and Palynology* **80**, 131-147.

*EISAWI, A. & SCHRANK, E. (2008). Upper Cretaceous to Neogene palynology of the Melut Basin, Southeast Sudan. *Palynology* **32**, 101-129.

*ELSIK, W. C. & DILCHER, D. L. (1974). Palynology and age of clays exposed in Larence clay pit, Henry County, Tennessee. *Palaeontographica Abteilung B* **146**, 66-87.

*FAIRCHILD, W. W. & ELSIK, W. C. (1970). Characteristic palynomorphs of the Lower Tertiary in the Gulf Coast. *Palaeontographica Abteilung B* **128**(3-6), 81-89.

FAN, M., FENG, R., GEISSMAN, J. W. & POULSEN, C. J. (2020). Late Paleogene emergence of a North American loess plateau. *Geology* **48**, 273-277.

*FARABEE, M. J. & CANRIGHT, J. E. (1986). Stratigraphic palynology of the lower part of the lance formation (Maestrichtian) of Wyoming. *Palaeontographica B* **199**, 1-89.

*FASSETT, J. E. (2009). New geochronologic and stratigraphic evidence confirms the Paleocene age of the dinosaur-bearing Ojo Alamo sandstone and animas formation in the San Juan Basin, New Mexico and Colorado. *Palaeontologia Electronica* **12**, 3A.

*FASSETT, J. E. & HINDS, J. S. (1971). Geology and fuel resources of the Fruitland formation and Kirtland Shale of the San Juan basin, New Mexico and Colorado. *Geological Survey Professional Paper* **676**, 1-76.

FERGUSON, D. K., PINGEN, M., ZETTER, R. & HOFMANN, C. C. (1998). Advances in our knowledge of the Miocene plant assemblage from Kreuzau, Germany. *Review of Palaeobotany and Palynology* **101**, 147-177.

*FREDERIKSEN, N. O. (1979). Paleogene sporomorph biostratigraphy, Northeastern Virginia. *Palynology* **3**, 129-167.

FREDERIKSEN, N. O. (1980). *Sporomorphs from the Jackson Group (Upper Eocene) and Adjacent Strata of Mississippi and Western Alabama*. US Government Printing Office, Washington, D.C.

*FREDERIKSEN, N. O., AGER, T. A. & EDWARDS, L. E. (1988). Palynology of Maastrichtian and Paleocene rocks, lower Colville River region, North Slope of Alaska. *Canadian Journal of Earth Science* **25**, 512-527.

FRIS, E. M., CRANE, P. R. & PEDERSEN, K. R. (2011). *Early Flowers and Angiosperm Evolution*. Cambridge University Press, Cambridge.

GARCIA, M. J., PREMAOR, E., OLIVEIRA, P. E. D., BERNARDES-DE-OLIVEIRA, M. E. C., DINO, R., ANTONIOLI, L. & MENEZES, J. B. D. (2016). Cenozoic distribution of Ephedripites Bolkhovitina (1953) ex Potonić (1958) emend. Krutzsch (1961) in Brazil. *Grana* **55**, 52-70.

GBIF (2022). GBIF Occurrence Download. https://doi.org/10.15468/dt dl teqcau
Accessed 4 November 2022.

*GHOSH, A. K., BANERJI, D. & SRIVASTAVA, S. K. (1963). Ephedra-type pollen grains in the Dharamsala (tertiary) formations, Punjab, India. *Nature* **198**, 408.

*GRAHAM, A. (1999). Studies in neotropical paleobotany. XIII an Oligo-Miocene palynoflora from Simojovel (Chiapas, Mexico). *American Journal of Botany* **86**, 17-31.

*GRAHAM, A., COZADD, D., AREGES-MALLEA, A. & FREDERIKSEN, N. O. (2000). Studies in neotropical paleobotany XIV. A palynoflora from the middle Eocene Saramaguacán formation of Cuba. *American Journal of Botany* **87**, 1526-1539.

*GRAHAM, A. & JARZEN, D. M. (1969). Studies in neotropical paleobotany. I. The Oligocene communities of Puerto Rico. *Annals of the Missouri Botanical Garden* **56**, 308-357.

*GRAY, J. (1960). Temperate pollen genera in the Eocene (Claiborne) flora. Alabama. *Science* **132**, 808-810.

GREENWOOD, P. E. & NIKULIN, M. S. (1996). *A Guide to Chi-Squared Testing*. John Wiley & Sons, Hoboken, NJ.

*GRIMSSON, F., ZETTER, R. & BAAL, C. (2011). Combined LM and SEM study of the Middle Miocene (Sarmatian) palynoflora from the Lavanttal Basin, Austria: part I. Bryophyta, Lycopodiophyta, Pteridophyta, Ginkophyta, and Gnetophyta. *Grana* **50**, 102-128.

*GUERSTEIN, G. R., GULER, M. V. & CASADÍO, S. (2004). Palynostratigraphy and palaeoenvironments across the Oligocene-Miocene boundary within the Centina
formation, southwestern Argentina. *Geological Society, London, Special Publications* **230**, 325–343.

HABIB, D. (1970). Middle cretaceous palynomorph assemblages from clays near the horizon beta deep-sea outcrop. *Micropaleontology* **16**, 345–379.

HAN, F., RYDIN, C., BOLINDER, K., DUPONT-NIVET, G., ABELS, H. A., KOUTSODENDRIS, A., ZHANG, K. & HOORN, C. (2016). Steppe development on the Northern Tibetan plateau inferred from Paleogene ephedroid pollen. *Grana* **55**, 71–100.

*HANSEN, B. C. S., GRIMM, E. C. & WATTS, W. A. (2001). Palynology of the Peace Creek site, Polk County, Florida. *GSA Bulletin* **113**, 682–692.

*HARRINGTON, G. J. (2003). Wasatchian (early Eocene) pollen from the red hot truck stop, Mississippi, USA. *Palaeontology* **46**, 725–738.

*HICKEY, L. J. (1977). Stratigraphy and paleobotany of the Golden Valley Formation (Early Tertiary) of western Dakota. *Memoir of the Geological Society of America* **150**, 1–183.

HOFMANN, C.-C., ROBERTS, E. A. & SEYFULLAH, L. J. (2022). Diversity of the dispersed Gnetalean pollen record from the Lower Cretaceous Crato Formation, Brazil: entomophily, harmomegathy and habitat heterogeneity. *Cretaceous Research* **129**, 105020.

*HOORN, C. (1994). Fluvial palaeoenvironments in the intracratonic Amazonas Basin (early Miocene-early middle Miocene, Colombia). *Palaeogeography, Palaeoclimatology, Palaeoecology* **109**, 1–54.

HOORN, C., STRAATHOF, J., ABELS, H. A., XU, Y. D., UTESCHER, T. & DUPONT-NIVET, G. (2012). A late Eocene palynological record of climate change and Tibetan Plateau uplift (Xining Basin, China). *Palaeogeography Palaeoclimatology Palaeoecology* **344**, 16–38.

*HORTON, B. K. (2004). Mesozoic-Cenozoic evolution of the Xining-Minhe and Dangchang basins, northeastern Tibetan Plateau: Magnetostratigraphic and biostratigraphic results. *Journal of Geophysical Research* **109**, B04402.

HUANG, J. & PRICE, R. A. (2003). Estimation of the age of extant Ephedra using chloroplast rbcL sequence datadata. *Molecular Biology and Evolution* **20**, 435–440.

*IBRAHIM, M. I. A. (2002). Late Albian-middle Cenomanian palynofacies and palynostratigraphy, Abu Gharadig-5 well, Western Desert, Egypt. *Cretaceous Research* **23**, 775–788.

*IBRAHIM, M. I. A. & ABDEL-KIREEM, M. R. (1997). Late Cretaceous palynofloras and foraminifera from Ain El-Wadi area, Farafra Oasis, Egypt. *Cretaceous Research* **18**, 633–660.

*ICKERT-BOND, S. M. & RENNER, S. S. (2016). The Gnetales: recent insights on their morphology, reproductive biology, chromosome numbers, biogeography, and divergence times. *Journal of Systematics and Evolution* **54**, 1–16.

*ICKERT-BOND, S. M., RYDIN, C. & RENNER, S. S. (2009). A fossil-calibrated relaxed clock for Ephedra indicates an Oligocene age for the divergence of Asian and New World clades and Miocene dispersal into South America. *Journal of Systematics and Evolution* **47**, 444–456.

IPCC (2023). *Climate change 2023: Synthesis report. contribution of working groups I, II and III to the sixth assessment report of the intergovernmental panel on climate change*. Report, The Australian National University.

*IVANOV, D. & SLAVOMIROVA, E. (2004). Palynological data on late Neogene vegetation from Karlovo Basin (Bulgaria): first results. *Comptes Rendus de l'Académie Bulgare des Sciences* **57**, 65–70.

IVARSSON, L. N. (2013). Pollen morphology in Ephedra (Gnetales) and implications for understanding fossil ephedroid pollen from the Tibetan Plateau, using a phylogenetic approach. Master's Thesis: Stockholm University.

*JARAMILLO, C. A., BAYONA, G., PARDO-TRUJILLO, A., RUEDA, M., TORRES, V., HARRINGTON, G. J. & MORA, G. (2007). The palynology of the Cerrejón formation (upper Paleocene) of northern Colombia. *Palynology* **31**, 153–189.

JARZEN, D. M., CORBETT, S. L. & MANCHESTER, S. R. (2010). Palynology and paleoecology of the middle Miocene Alum Bluff flora, Liberty County, Florida, USA. *Palynology* **34**, 261–286.

*JARZEN, D. M. & DILCHER, D. L. (2006). Middle Eocene terrestrial palynomorphs from the Dolime Minerals and Gulf Hammock quarries, Florida, USA. *Palynology* **30**, 89–110.

*JIMÉNEZ-MORENO, G., FAUQUETTE, S. & SUC, J.-P. (2008). Vegetation, climate and palaeoaltitude reconstructions of the Eastern Alps during the Miocene based on pollen records from Austria, Central Europe. *Journal of Biogeography* **35**, 1638–1649.

*KAYSERİ-OZER, M. S., AKGÜN, F., MAYDA, S. & KAYA, T. (2014). Palynofloras and vertebrates from Mušla-Oren region (SW Turkey) and palaeoclimate of the middle Burdigalian–Langhian period in Turkey. *Bulletin of Geosciences* **89**, 137–162.

KAYA, M. Y., DUPONT-NIVET, G., PROUST, J. N., ROPERCH, P., BOUGEOIS, L., MEIJER, N., FRIELING, J., FIORONI, C., ÖZKAN ALTINER, S., VARDAR, E., BARBOLINI, N., STOICA, M., AMINOV, J., MAMTIMIN, M. & ZHAOJIE, G. (2019). Paleogene evolution and demise of the proto-Paratethus Sea in Central Asia (Tarim and Tajik basins): role of intensified tectonic activity at ca. 41 ma. *Basin Research* **31**, 1–26.

KNIGHT, T. M., ASHMAN, T.-L., BENNETT, J. M., BURNS, J. H., PASSONNEAU, S. & STEETS, J. A. (2018). Reflections on, and visions for, the changing field of pollination ecology. *Ecology Letters* **21**, 1282–1295.

*KOVAR-EDER, J., MELLER, B. & ZETTER, R. (1998). Comparative investigations on the basal fossiliferous layers at the opencast mine Oberdorf (Koflach-Voitsberg lignite deposit, Styria, Austria; early Miocene). *Review of Palaeobotany and Palynology* **101**, 125–145.

KRASSILOV, V. A., RASNITSYN, A. P. & AFONIN, S. A. (2007). Pollen eaters and pollen morphology: co-evolution through the Permian and Mesozoic. *African Invertebrates* **48**, 3–11.

KRASSILOV, V. A., ZHERIKHIN, V. V. & RASNITSYN, A. P. (1997). Classopollis in the guts of Jurassic insects. *Palaeontology* **40**, 1095–1101.

*KUJAU, A., HEIMHOFER, U., HOCHULI, P. A., PAULY, S., MORALES, C., ADATTE, T., FÖLLMI, K., PLOCH, I. & MUTTERLOSE, J. (2013). Reconstructing Valanginian (early cretaceous) mid-latitude vegetation and climate dynamics based on spore-pollen assemblages. *Review of Palaeobotany and Palynology* **197**, 50–69.

LABANDEIRA, C. C., KVAČEK, J. & MOSTOVSKI, M. B. (2007). Pollination drops, pollen, and insect pollination of Mesozoic gymnosperms. *Taxon* **56**, 663–695.

LAND, W. J. G. (1913). Vegetative reproduction in an ephedra. *Botanical Gazette* **55**, 439–445.

*LEE, D. E., CONRAN, J. G., LINDQVIST, J. K., BANNISTER, J. M. & MILDENHALL, D. C. (2012). New Zealand Eocene, Oligocene and Miocene macrofossil and pollen records and modern plant distributions in the Southern Hemisphere. *Botanical Review* **78**, 235–260.

*LEOPOLD, E. B. & CLAY-POOLE, S. (2001). Florissant leaf and pollen floras of Colorado compared: climatic implications. In *Fossil Flora and Stratigraphy of the Florissant Formation, Colorado* (eds E. EVANOFF, K. M. GREGORY-WODZISKI and K. R. JOHNSON), pp. 17–70. Proceedings of the Denver Museum of Nature and Science, Denver, CO.

*LEOPOLD, E. B. & LIU, G. (1994). A long pollen sequence of Neogene age, Alaska range. *Quaternary International* **22**(23), 103–140.

LEOPOLD, E. B. & ZABORAC-REED, S. (2019). Pollen evidence of floristic turnover forced by cool aridity during the Oligocene in Colorado. *Geosphere* **15**, 254–294.

*LI, J. & BATTEN, D. J. (2004). Early cretaceous palynofloras from the Tanggula Mountains of the northern Qinghai-Xizang (Tibet) plateau, China. *Cretaceous Research* **25**, 531–542.

*LI, J. & BATTEN, D. J. (2011). Early cretaceous palynofloral provinces in China: western additions. *Island Arc* **20**, 35–42.

*LINDSEY, D. A., GLANZMAN, R. K., NÆSER, C. W. & NICHOLS, D. J. (1981). Upper Oligocene evaporites in basin fill of Sevier Desert region, Western Utah. *A&PG Bulletin* **65**, 251–260.

LOERA, I., SOSA, V. & ICKERT-BOND, S. M. (2012). Diversification in North American arid lands: niche conservatism, divergence and expansion of habitat explain speciation in the genus Ephedra. *Molecular Phylogenetics and Evolution* **65**, 437–450.

*LUDVIGSON, G. A., WITZKE, B. J., JOECKEL, R. M., RAVN, R. L., PHILLIPS, P. L., GONZÁLEZ, L. A. & BRENNER, R. L. (2010). New insights on the sequence stratigraphic architecture of the Dakota formation in Kansas-Nebraska-Iowa from a decade of sponsored research activity. *Bulletin (Kansas Geological Survey)* **258**, 1–35.

*LYSON, T. R., MILLER, I. M., BERCOVICI, A. D., WEISSENBURGER, K., FUENTES, A. J., CLYDE, W. C., HAGADORN, J. W., BUTRIM, M. J., JOHNSON, K. R., FLEMING, R. F., BARCLAY, R. S., MACCRACKEN, S. A., LOYD, B., WILSON, G. P., KRAUSE, D. W., ET AL. (2019). Exceptional continental record of biotic recovery after the Cretaceous–Paleogene mass extinction. *Science* **366**, 977–983.

*MACGINNIE, H. D. (1969). The Eocene Green River flora of northwestern Colorado and northeastern Utah. *University of California Publications in Geological Sciences* **83**, 1–140.

*MACPHAIL, M. K., HILL, R. S., FORSYTH, S. M. & WELLS, P. M. (1991). A late Oligocene-early Miocene cool climate flora in Tasmania. *Alcheringa* **15**, 87–106.

*MAHMOUD, M. S. (2003). Palynology and palaeoenvironment of the Quseir formation (Campanian) from central Egypt. *Journal of African Earth Sciences* **36**, 135–148.

*MAHMOUD, M. S. & DEAF, A. S. (2007). Cretaceous palynology (spores, pollen and dinoflagellate cysts) of the Siqefa 1-X borehole, northern Egypt. *Rivista Italiana di Paleontologia e Stratigrafia* **113**, 203–221.

*MAHMOUD, M. S. & MOAWAD, A.-R. M. M. (2000). Jurassic-cretaceous (Bathonian to Cenomanian) palynology and stratigraphy of the West Tiba-1 borehole, northern Western Desert, Egypt. *Journal of African Earth Sciences* **30**, 401–416.

*MARTIN, P. S. & GRAY, J. (1962). Pollen analysis and the Cenozoic. *Science* **137**, 103–111.

MASSONI, J., COUVREUR, T. L. & SAUQUET, H. (2015). Five major shifts of diversification through the long evolutionary history of Magnoliidae (angiosperms). *BMC Evolutionary Biology* **15**, 49.

*MEĐUS, J., COLOMBO, F. & DURAND, J. P. (1992). Pollen and spore assemblages of the uppermost cretaceous continental formations of souh-eastern France and north-eastern Spain. *Cretaceous Research* **13**, 119–132.
MEEUSE, A. D. J., DE MEIJER, A. H., MOHR, O. W. P. & WELLINGA, S. M. (1990). Entomophily in the dioecious gymnosperm Ephedra aphylla Forsk. (= E. Alte C. A.A.Mey.), with some notes on Ephedra campylopoda C.A.A.Mey. Iii. Further anthecological studies and relative importance of entomophilyentomophily. *Israel Journal of Botany* 39, 113–123.

MEIJER, N., DUPONT-NIVET, G., BARBOLINI, N., WOUTERSEN, A., ROHRMANN, A., ZHANG, Y., LIU, X., LICHT, A., ABELS, H. A., HOORN, C., TJALLINGH, R., ANDERMANN, C., DIETZE, M. & NOWACZYK, N. (2021). Loess-like dust appearance at 40 m a in Central China. *Paleoceanography and Paleoclimatology* 36, e2020PA003993.

MEIJER, N. & VAN DER MEULEN, B. (2023). Loss of loess in the geological record due to poor preservation. *Terra Nova* 35, 185–192.

METHNER, K., MULCH, A., FIEBIG, J., WACKER, U., GERDES, A., GRAHAM, S. A. & CHAMBERLAIN, C. P. (2016). Rapid middle Eocene temperature change in western North America. *Earth and Planetary Science Letters* 450, 132–139.

*MIAO, Y., FANG, X., HERRMANN, M., WU, F., ZHANG, Y. & LIU, D. (2011). Miocene pollen record of KC-1 core in the Qaidam Basin, NE Tibetan Plateau and implications for evolution of the East Asian monsoon. *Palaeogeography Palaeoclimatology Palaeoecology* 299, 30–38.

*MIAO, Y., FANG, X., LIU, Y.-S., YAN, X., LI, S. & XIA, W. (2016a). Late Cenozoic pollen concentration in the western Qaidam Basin, northern Tibetan Plateau, and its significance for paleoclimate and tectonics. *Review of Palaeobotany and Palynology* 231, 14–22.

*MIAO, Y., WU, F., CHANG, H., FANG, X., DENG, T., SUN, J. & JIN, C. (2016b). Alate-Eocene palynological record from the Hoh Xil Basin, northern Tibetan Plateau, and its implications for stratigraphic age, paleoclimate and paleoelevation. *Gondwana Research* 31, 241–252.

*MIAO, Y., WU, F., HERRMANN, M., YAN, X. & MENG, Q. (2013). Late early Oligocene East Asian summer monsoon in the NE Tibetan Plateau: evidence from a palynological record from the Lanzhou Basin, China. *Journal of Asian Earth Sciences* 75, 46–57.

MIX, H. T., MULCH, A., KENT-CORSON, M. L. & CHAMBERLAIN, C. P. (2011). Cenozoic migration of topography in the North American cordillera. *Geology* 39, 87–90.

*MOHR, B. R. & GEE, C. T. (1992). An early Alban palynoflora from the Kerguelen Plateau, southern Indian Ocean (leg 120). *Proceedings of the Ocean Drilling Program, Scientific Results* 120, 255–271.

*MORLEY, R. J. (1998). Palynological evidence for tertiary plant dispersals in the SE Asian region in relation to plate tectonics and climate. In *Biogeography and Geological Evolution of SE Asia* (eds R. HALL and J. D. HOLLOWAY), pp. 211–234. Backhuys Publishers, Leiden, The Netherlands.

MULCH, A., CHAMBERLAIN, C. P., COSCA, M. A., TEYSSIER, C., METHNER, K., HREN, M. T. & GRAHAM, S. A. (2015). Rapid change in high-elevation precipitation patterns of western North America during the middle eocene climatic optimum (MECO). *American Journal of Science* 315, 317–336.

*MÜLLER, H. (1966a). Palynological investigations of Cretaceous sediments in northeastern Brazil. *Proceedings of the Second West African Micropaleontological Colloquium, Ibadan* 1965, 123–136.

*MÜLLER, J. (1966b). Montane pollen from the Tertiary of NW. Borneo. *Blumea: Biodiversity, Evolution and Biogeography of Plants* 14, 231–235.

*MÜLLER, J. (1968). Palynology of the Pedawan and Plateau Sandstone formations (Cretaceous-Eocene) in Sarawak, Malaysia. *Micropaleontology* 14, 1–37.

*MYUNG, S. Y. (1989). *Palynology and paleoecology of Upper Cretaceous-Lower Tertiary strata Price Canyon, Utah (volumes I and II)*. PhD Thesis: Michigan State University.

*NARVÁEZ, P. L. & SABINO, I. F. (2008). Palynology of the Las Curiembres formation (late cretaceous, Salta Group Basin), Las Conchas Creek area, northwestern Argentina. *Ameghiniana* 45, 473–482.

*NELSON, R. E. & CARTER, L. D. (1985). Pollen analysis of a late Pliocene and early Pleistocene section from the Gubik formation of Arctic Alaska. *Quaternary Research* 24, 295–306.

*NICHOLS, D. J. (1994). A revised palynstratigraphic zonation of the nonmarine Upper Cretaceous, Rocky Mountain region, United States. In *Mesozoic Systems of the Rocky Mountain Region, USA* (eds M. V. CAPUTO, J. A. PETERSON and K. J. FRANCZYK), pp. 503–522. The Rocky Mountain Section, SEPM (Society for Sedimentary Geology), Tulsa, OK.

*NICHOLS, D. J. (2002). Palynology and microstratigraphy of the Hell Creek formation in North Dakota: a microfossil record of plants at the end of Cretaceous time. In *The Hell Creek Formation and the Cretaceous-Tertiary Boundary in the Northern Great Plains: An Integrated Continental Record of the End of the Cretaceous* (Volume 361, eds J. H. HARTMAN, K. R. JOHNSON and D. J. NICHOLS), pp. 95–143. Geological Society Special paper, Boulder, Colorado.

*NICHOLS, D. J. & FLEMING, R. F. (2002). Palynology and palynostratigraphy of Maastrichtian, Paleocene, and Eocene strata in the Denver Basin, Colorado. *Rocky Mountain Geology* 37, 135–163.

NIKLAS, K. J. (1985). The aerodynamics of wind pollination. *The Botanical Review* 51, 328–386.

NIKLAS, K. J. (2015). A biophysical perspective on the pollination biology of Ephedra nevadensis and *E. trifurca*. *The Botanical Review* 81, 28–41.

NIKLAS, K. J. & BUCHMANN, S. L. (1987). The aerodynamics of pollen capture in two sympatric Ephedra species. *Evolution* 41, 104–123.

NIKLAS, K. J., BUCHMANN, S. L. & KERCHNER, V. (1986). Aerodynamics of Ephedra trifurca: I. Pollengrain velocity fields around stems bearing ovulesovoles. *American Journal of Botany* 73, 966–979.

NIKLAS, K. J. & KERCHNER, V. (1986). Aerodynamics of Ephedra trifurca: II. Computer modelling of pollination efficiencies. *Journal of Mathematical Biology* 24, 1–24.

**NORTON, N. J. & HALL, J. W. (1969). Guide sporomorphae in the Upper Cretaceous-lower Tertiary of eastern Montana (USA). *Review of Palaeobotany and Palynology* 2(1-4), 99-110.

*OPÉBÓDÉ, M. O. (1987). Palynological dating of the Lamja Sandstone (Benue Basin, Nigeria) and its geological significance. *Journal of African Earth Sciences* 6, 421–426.

*OKUDA, M., NISHIDA, H., UEMURA, K. & YABE, A. (2006). Paleocene/Eocene pollen assemblages from the Ligorio Márquez formation, central Patagonia, XI region, Chile. In *Post-Cretaceous Floristic Changes in Southern Patagonia, Chile* (ed. H. NISHIDA), pp. 37–43. Chuo University, Tokyo.

PAGE, M., LICHT, A., DUPONT-NIVET, G., MEIJER, N., BARBOLINI, N., HOORN, C., SCHAUER, A., HUNTINGTON, K., BAJNAI, D., FIEBIG, J., MULCH, A. & GUO, Z. (2019). Synchronous cooling and decline in monsoonal rainfall in northeastern Tibet during the fall into the Oligocene icehouse. *Geology* 47, 103–206.

*PALAZZESI, L. & BARREDA, V. (2012). Fossil pollen records reveal a late rise of open-habitat ecosystems in Patagonia. *Nature Communications* 3, 1294.

PALMER, M. D., HARRIS, G. R. & GREGORY, J. M. (2018). Extending CMIP5 projections of global mean temperature change and sea level rise due to thermal expansion using a physically-based emulator. *Environmental Research Letters* 13, 84003.

*PALYNODATA INC. & WHITE, J. M. (2008). Palynodata datafile: 2006 version, with Introduction by J. M. White. Geological Survey of Canada Open File 5793, 1 CD-ROM.

*PANTI, C., MARENSSI, S. A. & OLIVERO, E. B. (2008). Paleogene flora of the Sloggett Formation, Tierra del Fuego, Argentina. *Ameghiniana* 45, 677–692.

*PETRESCU, I. & CODREA, V. (2004). The signification of the Paleocene microflora from Jibou (Salaj District) for the Paleogene palynological heritage of Romania. *Acta Palaeontologica Romaniae* 4, 351–360.

*PIEL, K. M. (1971). Palynology of oligocene sediments from central British Columbia. *Canadian Journal of Botany* 49, 1885-1920.

PIERCE, R. L. (1961). Lower upper cretaceous plant microfossils from Minnesota. *Minnesota Geological Survey Bulletin* 42, 1–86.

*PIETSCH, C., HARRISON, H. C. & ALLMON, W. D. (2016). Whence the Gosport sand (upper middle Eocene, Alabama)? The origin of glauconitic shell beds in the Paleogene of the U.S. gulf coastal plain. *Journal of Sedimentary Research* 86, 1249–1268.

POBLETE, F., DUPONT-NIVET, G., LICHT, A., VAN HINSBERGEN, D. J. J., ROPERCH, P., MIHALYNUK, M. G., JOHNSTON, S. T., GUILLOCHEAU, F., BABY, G., FLUTEAU, F., ROBIN, C., VAN DER LINDEN, T. J. M., RUIZ, D. & BAATSEN, M. L. J. (2021). Towards interactive global paleogeographic maps, new reconstructions at 60, 40 and 20 ma. *Earth-Science Reviews* 214, 1035-1058.

*POKNALL, D. T. (1982). Palynology of late Oligocene Pomahaka estuarine bed sediments, Waikoikoi, Southland, New Zealand. *New Zealand Journal of Botany* 20, 263-287.

POCOCK, S. A. J., VASANTHY, G. & VENKATACHALA, B. S. (1990). Pollen of Circumpolles—An enigma or morphotrends showing evolutionary adaptation. *Review of Palaeobotany and Palynology* 65, 179–193.

*POLE, M. & VAJDA, V. (2009). A new terrestrial Cretaceous-Paleogene site in New Zealand - turnover in macroflora confirmed by palynology. *Cretaceous Research* 30, 917-938.

POTTS, S. G., IMPERATRIZ-FONSECA, V., NGO, H. T., AIZEN, M. A., BIESMEIJER, J. C., BREEZE, T. D., DICKS, L. V., GARIBALDI, L. A., HILL, R., SETTELE, J. & VANBERGEN, A. J. (2016). Safeguarding pollinators and their values to human well-being. *Nature* 540, 220–229.

POTTS, S. G., NGO, H. T., BIESMEIJER, J. C., BREEZE, T. D., DICKS, L. V., GARIBALDI, L. A., HILL, R., SETTELE, J., VANBERGEN, A. (2016). *The assessment report of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services on pollinators, pollination and food production*. Bonn, Germany, Secretariat of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, 566 pp.

R DEVELOPMENT CORE TEAM (2023). *R: A Language and Environment for Statistical Computing*. R Foundation for Statistical Computing, Vienna, Austria. https://www.R-project.org/.

*RACHELE, L. D. (1976). Palynology of the Legler lignite: a deposit in the Tertiary Cohansey Formation of New Jersey, USA. *Review of Palaeobotany and Palynology* 22, 225-252.

*RAMÍREZ-ARRIAGA, E., PRÁMPARO, M. B., MARTÍNEZ-HERNÁNDEZ, E. & VALIENTE-BAUNET, A. (2006). Palynology of the Paleogene Cuayuca formation
(stratotype sections), southern Mexico: Chronostratigraphical and palaeoecological implications. *Review of Palaeobotany and Palynology* **141**, 259-275.

REN, D., LABANDEIRA, C. C., SANTIAGO-BLAY, J. A., RASNITSYN, A., SHIH, C., BASHKUEV, A., LOGAN, M. A. V., HOTTON, C. L. & DILCHER, D. (2009). Aprobable pollination mode before angiospermsangiosperms: Eurasian, longlong-probosid scorpionflysscorpionflies. *Science* **326**, 840–847.

*ROEHLER, H. W. (1992). *Description and Correlation of Eocene Rocks in Stratigraphic Reference Sections for the Green River and Washakie Basins, Southwest Wyoming: Includes Analyses of Eocene Rocks in the Washakie Basin*. US Government Printing Office.

RYDIN, C., BLOKZIJL, R., THUREBORN, O. & WIKSTRÖM, N. (2021). Node ages, relationships, and phylogenomic incongruence in an ancient gymnosperm lineage – phylogeny of ephedra revisited. *Taxon* **70**, 701–719.

RYDIN, C. & BOLINDER, K. (2015). Moonlight pollination in the gymnosperm Ephedra (Gnetales). *Biology Letters* **11**, 20140993.

RYDIN, C. & FRIIS, E. M. (2010). A new Early Cretaceous relative of Gnetales: Siphonospermum simplex gen. et sp. nov. from the Yixian formation of Northeast China. *BMC Evolutionary Biology* **10**, 183.

RYDIN, C. & HOORN, C. (2016). The Gnetales: past and present. *Grana* **55**, 1–4.

RYDIN, C., KHODABANDEH, A. & ENDRESS, P. K. (2010). The female reproductive unit of *Ephedra* (Gnetales): comparative morphology and evolutionary perspectives. *Botanical Journal of the Linnean Society* **163**, 387–430.

RYDIN, C. & KORALL, P. (2009). Evolutionary relationships in *Ephedra* (Gnetales), with implications for seed plant phylogenyphylogeny. *International Journal of Plant Sciences* **170**, 1031–1043.

RYDIN, C., PEDERSEN, K. R., CRANE, P. R. & FRIIS, E. M. (2006a). Former diversity of *Ephedra* (Gnetales): evidence from early cretaceous seeds from Portugal and North America. *Annals of Botany* **98**, 123–140.

RYDIN, C., PEDERSEN, K. R. & FRIIS, E. M. (2004). On the evolutionary history of *Ephedra*: cretaceous fossils and extant molecules. *Proceedings of the National Academy of Sciences* **101**, 16571–16576.

RYDIN, C., WU, S. Q. & FRIIS, E. M. (2006b). Liaoxia Cao et S.Q.Wu (Gnetales): ephedroids from the early cretaceous Yixian formation in Liaoning, northeastern China. *Plant Systematics and Evolution* **262**, 239–265.

*SCAFATI, L., MELENDI, D. L. & VOLKHEIMER, W. (2009). A Danian subtropical lacustrine palynobiota from South America (Bororó formation, san Jorge Basin, Patagonia - Argentina). *Geologica Acta* **7**, 35–61.

*SCHRANK, E. (2010). Pollen and spores from the Tendaguru Beds, Upper Jurassic and Lower Cretaceous of southeast Tanzania: palynostratigraphical and paleoecological implications. *Palynology* **34**, 3–42.

*SCHWEGER, C., FROESE, D., WHITE, J. M. & WESTGATE, J. A. (2011). Pre-glacial and interglacial pollen records over the last 3 ma from northwest Canada: why do Holocene forests differ from those of previous interglaciations? *Quaternary Science Reviews* **30**, 2124–2133.

SETTELE, J., BISHOP, J. & POTTS, S. G. (2016). Climate change impacts on pollination. *Nature Plants* **2**, 1–3.

*SHU, J.-W., WANG, W.-M., LEOPOLD, E. B., WANG, J.-S. & YIN, D.-S. (2008). Pollen stratigraphy of coal-bearing deposits in the Neogene Jidong Basin, Heilongjiang Province, NE China: new insights on palaeoenvironment and age. *Review of Palaeobotany and Palynology* **148**, 163–183.

*SINANOGLU, E. (1984). Early cretaceous palynomorphs from the Zuata area, eastern Venezuela. *Boletim Instituto Geociências, Universidade de São Paulo* esp. **15**, 116–128.

*SINGH, C. (1964). Microflora of the lower cretaceous Mannville group, East-Central Alberta. *Research Council of Alberta, RCA/AGS Bulletin* **15**, 1–255.

*SLODKOWSKA, B. (2009). Palynology of the Palaeogene and Neogene from the Warmia and Mazury areas (NE Poland). *Geologos* **15**, 219–234.

*SMITH, V., WARNY, S., JARZEN, D. M., DEMCHUK, T. & VAJDA, V. (2020). Palaeocene–Eocene mioscores from the Chicukul impact crater, Mexico. Part 1: spores and gymnosperm pollen. *Palynology* **44**, 473–487.

*SOARES, E. A. A., DINO, R., SOARES, D. P., ANTONIOLI, L. & DA SILVA, M. A. L. (2015). New sedimentological and palynological data from surface Miocene strata in the central Amazonas Basin area. *Brazilian Journal of Geology* **45**, 337–357.

*SONG, B., ZHANG, K., HAN, F., LIU, Z., AI, K., LI, S., XU, Y. & YANG, T. (2021). Reconstruction of the latest Eocene-early Oligocene paleoenvironment in the Hoh Xil Basin (Central Tibet) based on palynological and ostracod records. *Journal of Asian Earth Sciences* **217**, 104860.

SONG, Z., ZHENG, Y., LI, M., ZHANG, Y., WANG, W., WANG, D., ZHAO, C., ZHOU, S., ZHU, Z. & ZHAO, Y. (1999). *Fossil Spores and Pollen of China, Vol 1: The Late Cretaceous and Tertiary Spores and Pollen*. Science Press, Beijing.

*STAISCH, L. M., NIEMI, N. A., HONG, C., CLARK, M. K., ROWLEY, D. B. & CURRIE, B. (2014). A Cretaceous-Eocene depositional age for the Fenghuoshan group, Hoh Xil Basin: implications for the tectonic evolution of the northern Tibet plateau. *Tectonics* **33**, 281–301.

STEEVES, M. W. & BARGHOORN, E. S. (1959). The pollen of Ephedra. *Journal of the Arnold Arboretum* **40**, 221–259.

STEINTHORSDOTTIR, M., COXALL, H. K., DE BOER, A. M., HUBER, M., BARBOLINI, N., BRADSHAW, C. D., BURLS, N. J., FEAKINS, S. J., GASSON, E.,

HENDERIKS, J., HOLBOURN, A. E., KIEL, S., KOHN, M. J., KNORR, G., KÜRSCHNER, W. M., *et al.* (2021). The Miocene: the future of the pastpast. *Palaeogeography and Palaeoclimatology* **36**, e2020PA004037.

*STONE, J. F. (1971). *Palynology of the almond formation (Upper Cretaceous), Rock Springs Uplift, Wyoming*. PhD Thesis: Michigan State University.

*SUN, J., NI, X., BI, S., WU, W., YE, J., MENG, J. & WINDLEY, B. F. (2014). Synchronous turnover of flora, fauna, and climate at the Eocene–Oligocene Boundary in Asia. *Scientific Reports* **4**, 7463.

SUN, X. & WANG, P. (2005). How old is the Asian monsoon system?—Palaeobotanical records from China. *Palaeogeography, Palaeoclimatology, Palaeoecology* **222**, 181–222.

*SUN, J. & ZHANG, Z. (2008). Palynological evidence for the mid-Miocene climatic optimum recorded in Cenozoic sediments of the Tian Shan range, northwestern China. *Global and Planetary Change* **64**, 53–68.

*TAKAHASHI, M. (1997). Fossil spores and pollen grains of Cretaceous (upper Campanian) from Sakhalin, Russia. *Journal of Plant Research* **110**, 283–298.

*TANRIKULU, S., DOYLE, J. A. & DELUSINA, I. (2018). Early cretaceous (Albian) spores and pollen from the Glen Rose Formation of Texas and their significance for correlation of the Potomac group. *Palynology* **42**, 438–456.

*TEW, B. H. (1992). *Sequence Stratigraphy, Lithofacies Relationships, and Paleogeography of Oligocene Strata in Southeastern Mississippi and Southwestern Alabama*. Geological Survey of Alabama, Stratigraphy and Paleontology Division.

TOSOLINI, A.-M. P., MCLOUGHLIN, S., WAGSTAFF, B. E., CANTRILL, D. J. & GALLAGHER, S. J. (2015). Cheirolepidiacean foliage and pollen from cretaceous high-latitudes of southeastern Australia. *Gondwana Research* **27**, 960–977.

TREVISAN, L. (1980). Ultrastructural notes and considerations on Ephedrites, Eucommiidites and Monosulcites pollen grains from Lower Cretaceous sediments of southern Tuscany (Italy). *Pollen et Spores* **22**, 85–132.

*TSCHUDY, R. H. (1973). *Stratigraphic Distribution of Significant Eocene Palynomorphs of the Mississippi Embayment*. US Government Printing Office.

*VAJDA-SANTIVANEZ, V. (1999). Mioscores from Upper Cretaceous-Paleocene strata in northwestern Bolivia. *Palynology* **23**, 181–196.

VAKHAMEEV, V. (1981). Pollen Classopollen: indicator of Jurassic and Cretaceous climates. *Journal of Palaeosciences* **28**, 301–307.

*VAN HOEKEN-KLINKENBERG, P. M. J. (1964). A palynological investigation of some Upper Cretaceous sediments in Nigeria. *Pollen et Spores* **6**, 209–231.

*VAN HOEKEN-KLINKENBERG, P. M. J. (1966). Maastrichtian Paleocene and Eocene pollen and spores from Nigeria. *Leidse Geologische Mededelingen* **38**, 37–48.

*VOLKHEIMER, W., SCAFATI, L. & MELENDI, D. L. (2007). Palynology of a Danian warm climatic wetland in central northern Patagonia, Argentina. *Revista Espanol de Micropaleontologia* **39**, 117–134.

WANG, Z.-Q. (2004). A new Permian gnetalean cone as fossil evidence for supporting current molecular phylogenyphylogeny. *Annals of Botany* **94**, 281–288.

WANG, Y., MOSBRUGGER, V. & ZHANG, H. (2005). Early to Middle Jurassic vegetation and climatic events in the Qaidam Basin, Northwest China. *Palaeogeography, Palaeoclimatology, Palaeoecology* **224**, 200–216.

*WANG, W.-M., SAITO, T. & NAKAGAWA, T. (2001). Palynostratigraphy and climatic implications of Neogene deposits in the Himi area of Toyama Prefecture, Central Japan. *Review of Palaeobotany and Palynology* **117**, 281–295.

WANG, D.-N., SUN, X.-Y. & ZHAO, Y.-N. (1990a). Late cretaceous to Tertiary palynofloras in Xinjiang and Qinghai, China. *Review of Palaeobotany and Palynology* **65**, 95–104.

WANG, D.-N., SUN, X.-Y., ZHAO, Y.-N. & HE, Z. (1990b). *The Study on the Micropaleobotany from Cretaceous–Tertiary of the Oil Bearing Basins in Some Regions of Qinghai and Xinjiang*. China Environmental Science Press, Beijing.

WANG, K., ZHANG, Y. & JIANG, H. (1982). Sporo-pollen assemblage of the Late Cretaceous from Zhucheng county, Shandong Province. *Chinese Journal of Geology* **3**, 336–338.

WATTS, W. A. (1985). A long pollen record from Laghi di Monticchio, southern Italy: a preliminary account. *Journal of the Geological Society of London* **142**, 491–499.

WESTERHOLD, T., MARWAN, N., DRURY, A. J., LIEBRAND, D., AGNINI, C., ANAGNOSTOU, E., BARNET, J. S. K., BOHATY, S. M., DE VLEESCHOUWER, D., FLORINDO, F., FREDERICHS, T., HODELL, D. A., HOLBOURN, A. E., KROON, D., LAURETANO, V., *et al.* (2020). An astronomically dated record of Earth's climate and its predictability over the last 66 million years. *Science* **369**, 1383–1387.

*WHITLOCK, C. & DAWSON, M. R. (1990). Pollen and vertebrates of the early Neogene Haughton formation, Devon Island, arctic Canada. *Arctic* **43**, 324–330.

*WINGATE, F. H. (1983). Palynology and age of the Elko formation (Eocene) near Elko, Nevada. *Palynology* **7**, 93–132.

*WINGATE, F. H. & NICHOLS, D. J. (2001). Palynology of the uppermost Eocene lacustrine deposits at Florissant National Monument, Colorado. In *Fossil Flora and Stratigraphy of the Florissant Formation, Colorado* (eds E. EVANOFF, K. M. GREGORY-WODZICKI and K. R. JOHNSON), pp. 71–135. Proceedings of the Denver Museum of Nature and Science.

WODEHOUSE, R. P. (1933). Tertiary Pollen-II the oil shales of the Eocene Green River formation. *Bulletin of the Torrey Botanical Club* **60**, 479–524.

*XU, J.-X., FERGUSON, D. K., LI, C.-S., WANG, Y.-F. & DU, N.-Q. (2004). Climatic and ecological implications of late Pliocene palynoflora from Longling, Yunnan, China. *Quaternary International* **117**, 91–103.
*YI, S. & BATTEN, D. J. (2002). Palynology of Upper Cretaceous (uppermost Campanian-Maastrichtian) deposits in the South Yellow Sea Basin, offshore Korea. *Cretaceous Research* **23**, 687–706.

*YUAN, Q., BARBOLINI, N., ASHWORTH, L., RYDIN, C., GAO, D.-L., SHAN, F.-S., ZHONG, X.-Y. & VAJDA, V. (2021). Palaeoenvironmental changes in Eocene Tibetan lake systems traced by geochemistry, sedimentology and palynofacies. *Journal of Asian Earth Sciences* **214**, 104778.

YUAN, Q., BARBOLINI, N., RYDIN, C., GAO, D.-L., WEI, H.-C., FAN, Q.-S., QIN, Z.-J., DU, Y.-S., SHAN, J.-J., SHAN, F.-S. & VAJDA, V. (2020). Aridification signatures from fossil pollen indicate a drying climate in east-central Tibet during the late Eocene. *Climate of the Past* **16**, 2255–2273.

*ZAMALOA, M. C. & ROMERO, E. J. (1990). Some spores and pollen from the Cullen formation (upper Eocene to middle Oligocene), Tierra del Fuego, Argentina. *Palynology* **14**, 123–133.

*ZETTER, R., HESSE, M. & HUBER, K. H. (2002). Combined LM, SEM and TEM studies of Late Cretaceous pollen and spores from Gmünd, Lower Austria. *Staphia* **80**, 201–230.

ZHANG, M., HOU, X., DU, B., JI, L., DU, Z. & WANG, S. (2019). The first palynological records from the Lower Cretaceous of the northern Sichuan Basin, China: Palyn stratigraphical and paleoenvironmental significance. *Journal of Asian Earth Sciences* **174**, 177–188.

*ZHANG, W., FANG, X., ZHANG, T., SONG, C. & YAN, M. (2020). Eocene rotation of the northeastern central Tibetan Plateau indicating stepwise compressions and eastward extrusions. *Geophysical Research Letters* **47**, e2020GL088989.

*ZHANG, W. L. (2006). *The High Precise Cenozoic Magnetostratigraphy of the Qaidam Basin and Uplift of the Northern Tibetan Plateau*, pp. 108–109. Lanzhou University, Lanzhou, China.

ZHANG, Y. & ZHAN, J. (1991). *Late Cretaceous and Early Tertiary Spores and Pollen from the Western Tarim Basin*, S. Science Press, Beijing.

*ZHANG, Z. & SUN, J. (2011). Palynological evidence for Neogene environmental change in the foreland basin of the southern Tianshan range, northwestern China. *Global and Planetary Change* **75**, 56–66.

ZHU, Z., WU, L., XI, P., SONG, Z. & ZHANG, Y. (1985). *A Research on Tertiary Palynology from the Qaidam Basin, Qinghai Province* (eds Z. H. ZHU, L. WU, P. XI, Z. C. SONG and Y. Y. ZHANG). The Petroleum Industry Press, Beijing, China.

## IX. SUPPORTING INFORMATION

Additional supporting information may be found online in the Supporting Information section at the end of the article.

**Table S1.** Global distribution of ephedroids through time.

**Table S2.** North American ephedroid palaeopolynomorphs.

**Table S3.** Central Asian ephedroid pollen data.

*(Received 2 November 2023; revised 5 February 2025; accepted 19 February 2025)*