Southern-Hemisphere terrestrial communities from the early Paleocene are poorly known, but recent work on Danian plant fossils from the Salamanca Formation in Chubut Province, Argentina are providing critical data on earliest Paleocene floras. The fossils described here come from a site in the Salamanca Formation dating to ca. 1 million years or less after the end-Cretaceous extinction event; they are the first fossil flowers reported from the Danian of South America, and possible the entire Southern Hemisphere. They are compressions and impressions in flat-laminated light gray shale, and they belong to the family Rhamnaceae (buckthorns). Flowers of Notiantha grandensis gen. et sp. nov. are pentamerous, with distinctly keeled calyx lobes projecting from the hypanthium, clawed and cucullate emarginate petals, antepetalous stamens, and a pentagonal floral disk that fills the hypanthium. Their phylogenetic position was evaluated using a molecular scaffold approach combined with morphological data. Results indicate that the flowers are most like those of extant ziziphoid Rhamnaceae. The associated leaves, assigned to Suessenia grandensis gen. et sp. nov. are simple and ovate, with serrate margins and three acrodromous basal veins. They conform to the distinctive leaves of some extant Rhamnaceae in the ziziphoid and ampelozizyphoid clades. These fossils provide the first unequivocal megafossil evidence of Rhamnaceae in the Southern Hemisphere, demonstrating that Rhamnaceae expanded beyond the tropics by the earliest Paleocene. Given previous reports of rhamnaceous pollen in the late Paleogene and Neogene of Antarctica and southern Australia, this new occurrence increases the possibility of high-latitude dispersal of this family between South America and Australia via Antarctica during the Cenozoic.
Citation: Jud NA, Gandolfo MA, Iglesias A, Wilf P (2017) Flowering after disaster: Early Danian buckthorn (Rhamnaceae) flowers and leaves from Patagonia. PLoS ONE 12(5): e0176164. https://doi.org/10.1371/journal.pone.0176164
Editor: William Oki Wong, Institute of Botany, CHINA
Received: November 13, 2016; Accepted: March 1, 2017; Published: May 10, 2017
Copyright: © 2017 Jud et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: The complete matrix of morphological data is available online at the MorphoBank website (project P2506, Morphology of Rhamnaceae (flowers and leaves) [matrix 24392]; http://morphobank.org/permalink/?P24392).
Funding: Funded by National Science Foundation DEB-1556136 to MAG www.nsf.gov, National Science Foundation DEB-0918932 to MAG www.nsf.gov, National Science Foundation DEB-1556666 to NRC and PW www.nsf.gov, National Science Foundation DEB-0919071 to NRC and PW www.nsf.gov, National Science Foundation DEB-0345750 to NRC, PW and MAG www.nsf.gov, David and Lucile Packard Foundation to PW, Fulbright Foundation to MAG.
Competing interests: The authors have declared that no competing interests exist.
The Salamanca Formation is an estuarine unit in the San Jorge Basin of southern Argentina that yields well-preserved, well-dated fossils from the early Paleocene. Studies of these fossils are providing new data on plant and animal diversity following the end-Cretaceous extinction event [1–19]. Here, we report the first fossil flowers from an early Danian (~65Ma) assemblage in the Southern Hemisphere and show that they are attributable to Rhamnaceae. Extant Rhamnaceae Juss. comprise 54 genera and over 900 species of shrubs, trees, lianas, and perennial herbs that are easily identified for their unusual combination of floral characters [20–23]. Traditionally, the family was subdivided into five tribes differentiated based on fruit types [24,25]; however, recent molecular phylogenetic studies suggest that these were not natural groups . Instead, the family is now divided into 11 tribes that are distinguished by combinations of vegetative and reproductive character states, with a handful of genera still unplaced at the tribal level [21–23,26,27]. The tribes and unplaced genera belong to three major clades that are informally known as the rhamnoids, ziziphoids, and ampelozizyphoids; however, morphological synapomorphies for these three groups have not been identified so far . Despite recent advances in understanding the systematics of living Rhamnaceae, many aspects of their early evolution and biogeographic history remain unclear [22,23,28–30].
In the last decade, the fossil record of Rhamnaceae has grown significantly (Fig 1; Table 1), and several occurrences have confirmed at least a Late Cretaceous origin for the family [28,31]. Fossil remains assigned to extant genera have been reported from Eocene and younger deposits, including the distinctive fruits of Paliurus Mill. [32–41], Berchemia Neck. ex DC. , and Ventilago Gaertn. [31,43], the wood and leaves of Hovenia Thunb. [37,44–46]; and the distinctive leaves of Ceanothus L. [38,47–50] and Colubrina Rich. ex Brongn. [51,52]. These fossils provide minimum age estimates for the diversification of crown-group Rhamnaceae, and several have been used to calibrate trees in recent molecular phylogenetic analyses [29,53,54].
Gray area indicates the distribution of extant Rhamnaceae. The shapes correspond to different fossilized plant organs and the colors represent different ages. The fossil flowers and leaves described here were collected from the Rancho Grande site in Chubut Argentina. Details of all occurrences shown here are listed in Table 1. The base map was created with Natural Earth Dataset.
Occurrences of fossils attributed to Rhamnaceae, excluding those based on leaf compressions alone.
Whereas some authors have suggested a Laurasian origin for the Rhamnaceae family , Richardson et al.  concluded that a Gondwanan origin during the Paleogene is more parsimonious for the ziziphoid and the ampelozizyphoid clades. Most recently, Onstein et al. [26,56] concluded that crown-group Rhamnaceae began to diversify in the tropical rainforest biome during the Cretaceous, rather than the Paleogene [53,57], but also that much of the modern richness can be attributed to relatively recent (latest Paleogene to Neogene) diversification in Mediterranean-type ecosystems.
The fossil flowers reported here are adpressions, and they have a combination of character states similar to members of the ziziphoid clade and the tribe Paliureae Reissek ex Endl, but they do not match any extant genus. Although not in organic connection, the flowers were found in association with ziziphoid leaves, also described here. We use phylogenetic analysis to determine the relationship of these fossils to living members of the family and to test biogeographic hypotheses, including the idea that the Rhamnaceae originated in Laurasia.
The Salamanca Formation crops out in the San Jorge Basin in southern Chubut and northern Santa Cruz provinces, Argentina, overlying the Cretaceous Chubut Group and underlying the Paleocene and Eocene Río Chico Group [10,17, 18, 58–61]. The formation yields abundant plant remains [2,3,8,9,15,16,19,62–65] as well as fossils of invertebrates [10,65–71], marine macrofaunas [72–74], reptiles [75–77], and mammals [1,4–7,11–14,78,79].
The fossils described here were collected from the Rancho Grande locality in Chubut, a single fossil quarry exposed along the banks of the Río Chico in the lower Salamanca Formation [17,18]. All necessary permits were obtained for the described study, which complied with all relevant regulations. The age of the Rancho Grande site is constrained to geomagnetic polarity chron C29n, or 65.58–64.86 Ma (early Danian) on the 2012 Geomagnetic Polarity Timescale [17,18,80]. The formation consists primarily of estuarine to shallow marine deposits, and the fossils were found in flat-laminated beds of very-fine sandstone to siltstone. The Rancho Grande beds were deposited in a tidal estuary near the seaward limit of tidal influence . Abundant angiosperm leaves, delicate flowers, and leafy herbaceous shoots characterize the assemblage. The presence of a diverse marine fauna including brittle stars, a benthic foraminifer, and bivalves in the same bedding planes suggests significant transport of the plant material from the original site of growth [39,46]
Palynological analysis of Danian deposits in northern Chubut Province revealed low floral diversity after the end-Cretaceous mass extinction, followed by a rapid recovery . Recent analysis of palynomorphs collected from the same temporal interval of the Salamanca Fm. as the fossil flowers and leaves described here (C29n) found that 50% of all pollen types are angiosperms, whereas gymnosperms accounted for only ~13% of total richness; however, Classopollis pollen, representing the extinct conifer family Cheirolepidiaceae, is the most abundant palynomorph in all samples . Wood assemblages from the Salamanca Fm. are dominated by conifers, but the presence of fossil angiosperm woods indicate that they were also part of the canopy [8,9,65]. The co-occurrence of palms [2,3,16,64,65,81], dicot woods with indistinct growth rings , and alligatorids [76,77], indicates temperature remained above freezing year-round. The results of leaf physiognomic analyses [15,82,83] indicate that the climate in the San Jorge Basin during the early Paleocene was warm subtropical.
Materials and methods
The fossil specimens are housed in the Paleobotanical collection of the Museo Paleontológico Egidio Feruglio (MPEF-Pb), Trelew, Chubut Province, Argentina, under these numbers: MPEF-Pb 8548a&b, MPEF-Pb 8549, MPEF-Pb 8551 (flowers), MPEF-Pb 8552, MPEF-Pb 8553, MPEF-Pb 8555, MPEF-Pb 8560, MPEF-Pb 8563 (leaves). The fossil flower specimens were prepared using standard degauging techniques, whereas the leaves required minimal preparation. Images of macroscopic features were captured with a Canon EOS 7D DSLR Camera, and microscopic details were photographed with a Nikon DS Fi1 camera mounted on a Nikon SMZ1000 stereoscope at the Museo Paleontológico Egidio Feruglio. Epifluorescence microscopy was used to check for the presence of pollen grains in the anthers. Images were processed with Adobe Photoshop (San Jose, California, USA). The fossils were compared with extant Rhamnaceae specimens obtained from the LH Bailey Hortorium Herbarium (BH), Department of Plant Biology, Cornell University, Ithaca, NY, USA, the U.S. National Herbarium (US), Smithsonian National Museum of Natural History, Washington DC, USA, the National Cleared Leaf Collection (NCLC-H) Smithsonian National Museum of Natural History, Washington DC, USA, and the University of Florida Herbarium (FLAS), University of Florida, Gainesville, FL, USA (S1 Table). Terminology for description of the leaves follows that of the Manual of Leaf Architecture .
To evaluate the phylogenetic affinities of the fossil flowers, and the plant concept based on both flowers and leaves, we assembled a new morphological matrix for Rhamnaceae modified from that of Calvillo-Canadell  as later published by Millán and Crepet . We compared the floral characters with those included in the studies by Aagesen , Richardson et al. , and Islam and Simmons . Based on these comparisons, we made several changes to the original matrix of morphological characters. First, we modified several characters to so that there are fewer alternative states and so that additional fossil and modern material is easier to score, but also so that the results are not in conflict with previous analyses. Second, we excluded characters that are not preserved in any of the fossil flowers because they would not influence the optimal position of the fossil-taxon on the scaffold topology. Third, we added three characters related to pubescence and floral disk morphology because these features are preserved on the fossils. Fourth, we added five foliar characters. Fifth, we scored character data for seven additional extant genera Sarcomphalus R. Browne emend. Hauenschild, Hovenia (Paliureae), Ventilago (Ventilagineae), Pomaderris Labill. (Pomaderreae), Noltea Rchb. (Phyliceae), Ampelozizyphus Duckey (Ampelozizypheae), Bathiorhamnus Capuron (Bathiorhamneae), and Helinus E. May. ex Endl. (Gouanieae Reissek ex Endl.). Finally, we scored character data for the fossil flowers and leaves. The matrix comprises 25 taxa, 25 floral characters, and five leaf characters. The complete matrix is available online at the MorphoBank website (project P2506, Morphology of Rhamnaceae (flowers and leaves) [matrix 24392]; http://morphobank.org/permalink/?P24392). Nine of the 11 tribes of Rhamnaceae are represented in this new matrix, as opposed to four tribes in the matrix used by Millán and Crepet . With the inclusion of Sarcomphalus (formerly new world Ziziphus Mill.) and Hovenia, the generic diversity of Paliureae is fully represented in this new dataset. Of the three monogeneric tribes in the ampelozizyphoid clade, Ampelozizyphus and Bathiorhamnus are included [88,89].
We analyzed the matrix using the molecular scaffold approach described by Springer et al.  to determine the most parsimonious position(s) first based on the fossil flowers alone, and then including the foliar characters. We used two different scaffolds to evaluated how sensitive the placement of the fossil is to tree topology. First, we constrained the tree searches such that the final topology is consistent with the relationships reported by Hauenschild et al. . The Hauenschild et al. topology is based on sequence data from one chloroplast marker (trnL-trnF) and one nuclear marker (ITS) for more than 400 species. Then, we constrained the tree searches such that the final topology is consistent with the relationships reported by Onstein et al. . The Onstein et al. topology is based sequence data from six chloroplast markers and one nuclear marker (ITS) for 280 species. All tree searches were implemented in the phylogenetic software TNT  using the parsimony ratchet . We constrained the searches by appending a set of binary characters that define the scaffold topology and weighting them to 99%. All characters were unordered, and only the position of the new taxon was free to vary. In the analyses, 10 sets of 200 iterations using a 10% perturbation of characters were used for the ratchet analyses, and default values for drift, sectorial search, and tree fusion were retained.
The electronic version of this article in Portable Document Format (PDF) in a work with an ISSN or ISBN will represent a published work according to the International Code of Nomenclature for algae, fungi, and plants, and hence the new names contained in the electronic publication of a PLOS article are effectively published under that Code from the electronic edition alone, so there is no longer any requirement to provide printed copies.
New names contained in this work have been submitted to IFPNI, from where they will be made available to the Global Names Index. The LSID IFPNI codes can be resolved and the associated information viewed through any standard web browser by appending the LSID contained in this publication to the prefix http://fossilplants.info/. The LSID for this publication is: http://fossilplants.info/publications/4B0FD041-D9CE-446E-B866-D201D710F412. The online version of this work is archived and available from the Dryad Digital Repository.
Order: Rosales Bercht. & J. Presl 1820
Family: Rhamnaceae Jussieu 1789
Genus: Notiantha Jud, Gandolfo, Iglesias & Wilf, gen. nov.
Type species: Notiantha grandensis Jud, Gandolfo, Iglesias & Wilf, sp. nov. (Fig 2).
(A) Flower in transverse view showing pentamerous structure, sepals triangular with a distinct keel, cucullate petals alternating with sepals, stamens antepetalous, and floral disk surrounding a coalified gynoecium. MPEF-Pb 8548a. (B) Counterpart of specimen in ‘A’ showing a sepal with a central keel and two marginal veins converging toward the apex (at arrow) MPEF-Pb 8548b. (C) Composite digital illustration of the flower created from ‘A’ and ‘B’. (D) Flower in longitudinal view showing slender pedicel, floral cup (at arrow), three preserved sepals, and a cucullate petal (at arrowhead). MPEF-Pb 8549. (E) Close-up of the petal in ‘D’ showing clawed structure and the longitudinally folded distal portion of the petal; the overlapping lobes are marked with arrows. MPEF-Pb 8549. (F) Flower in longitudinal view showing slender pedicel and three sepals. MPEF-Pb 8551. (G) Close-up of flower in ‘A’ showing the keeled sepal (at arrowhead), and the notched petal apex (at arrow). MPEF-Pb 8548a. (H) Close-up of flower in ‘A’ showing an anther opposite a petal, and a line suggesting where the anther filament adnate to the petal at its base (at arrow). MPEF-Pb 8548a. Scale bars: A-D, F = 2 mm; E = 0.5 mm; G, H = 1 mm.
Generic diagnosis: Pedicellate, pentamerous, actinomorphic, perfect flowers; hypanthium obconical, glabrous; calyx lobes five, lobes deltoid to ovate, keeled, inserted at the margin of the hypanthium; petals five, short-clawed, cucullate, curved, and equal in length to the calyx lobes, petal apex emarginate; stamens epipetalous, anthers dorsifixed and versatile; pentagonal floral disk filling the hypanthium.
Etymology: From the Greek nótios for southern, and anthos for flower.
Species: Notiantha grandensis Jud, Gandolfo, Iglesias & Wilf, sp. nov. Fig 2A–2H.
Holotype: MPEF-Pb 8548a,b.
Paratypes: MPEF-Pb 8549, MPEF-Pb 8551.
Repository: Museo Paleontológico Egidio Feruglio Paleobotany Collection (MPEF-Pb), Trelew City, Chubut, Argentina.
Type Locality: Rancho Grande, Chubut, Argentina.
Stratigraphic position: Lower Salamanca Formation.
Age: Paleocene, early Danian, geomagnetic polarity chron C29n (65.58–64.86 Ma).
Etymology of specific epithet: from the Rancho Grande locality.
Species diagnosis: as for the genus Notiantha.
Description: The flowers are pedicellate, pentamerous, actinomorphic, and perfect, 5–7 mm diameter (Fig 2A–2C) with a gamosepalous, obconical floral cup. The pedicel is slender, 2.5–4 mm long and 0.6 mm across (Fig 2D and 2F). The perianth is composed of calyx and corolla that have whorled phyllotaxy. The calyx lobes (sepals) are triangular to slightly ovate with acute and straight to slightly acuminate apex (Fig 2A–2C and 2F–2H), and they are 1.4–1.6 mm wide and 1.5–1.7 mm long. A distinct adaxial, longitudinal keel (Fig 2A–2D and 2F–2H) and two converging marginal veins are visible on each sepal (Fig 2B). The corolla is composed of short-clawed, cucullate petals (Fig 2A–2E) with an apical notch (i.e., emarginate apex; Fig 2G); they are either open (Fig 2G and 2H) or conduplicate (Fig 2E) and alternating with sepals (Fig 2A–2C); petals are 1.4 mm long, 0.1 mm wide at base and 0.6 mm at the widest part. The androecium has five antepetalous stamens (i.e. obhaplostemonous) (Fig 2A–2C), which are adnate to the petals at the base (Fig 2H); the filaments are slender, c. 1.2 mm long, and the anthers are dorsifixed and versatile and seem to have four microsporangia (Fig 2H). Pollen grains were not detected in the anthers. The gynoecium is poorly preserved, and the number of carpels and stylodia is unknown. In transverse view, the pentagonal area that is 1.9 mm across, darker than the sepals, and surrounds the coalified gynoecium is interpreted as a floral disk. The floral disk surrounds and covers much of the coalified gynoecium, suggesting that it is either semi-inferior or inferior.
Genus: Suessenia Jud, Gandolfo, Iglesias & Wilf, gen. nov.
Type Species: Suessenia grandensis Jud, Gandolfo, Iglesias & Wilf, sp. nov. (Fig 3).
(A) S. grandensis MPEF-Pb 8553 showing overall shape, stout petiole, acute base (at arrow), serrate margin, and acrodromous primary veins. (B) S. grandensis MPEF-Pb 8560 showing its shape, acute to attenuate apex (at arrow), serrate margin, and acrodromous primary veins. (C) S. grandensis MPEF-Pb 8555 showing overall shape, petiole, acute base, serrate margin, and acrodromous primary veins. (D) Close-up of the leaf blade (MPEF-Pb 8552) showing mixed percurrent epimedial tertiary veins running between the medial primary vein (mp) and the lateral primary vein (lp). Note that they form an acute angle to the medial primary vein. (E). S. grandensis MPEF 8563 overall shape, petiole, acute base, serrate margin, and acrodromous primary veins, and an asymmetric, obtuse apex. (F) Close-up of the margin in ‘E’ showing exterior tertiary veins that are looped or terminating at the margin; note the glandular tooth apex (at arrow). (G) Leaf of Sarcomphalus saeri (Pittier) Hauenschild US 2045934 showing ovate blade, petiole, rounded base, acute apex, serrate margin, three acrodromous primary veins, and alternate percurrent epimedial tertiary veins. (H) Leaf of S. saeri US 3554997 showing ovate blade, petiole, rounded base, acute apex, serrate margin with apically oriented teeth, three acrodromous primary veins, distal major secondary veins, and alternate percurrent epimedial tertiary veins. (I) Cleared leaf of Ziziphus sativa Gaertn. (junior synonym of Z. jujuba Miller) NCLC-H 1791 showing ovate to elliptic blade, acute base, acute apex, serrate margin with apically oriented teeth, three acrodromous primary veins. (J) Close-up of the leaf in ‘I’ showing the apically oriented glandular teeth. Note the similarity to ‘F.’ Scale bars: A, B, H = 10 mm; C, E = 5 mm; D = 3 mm; F, J = 2 mm; G = 15 mm; I = 40 mm.
Generic Diagnosis: Leaves simple, marginal petiolate; blade shape ovate to elliptic; base obtuse, rounded, symmetrical or slightly asymmetrical, apex acute or obtuse; margin unlobed, toothed; primary vein framework basal acrodromous, with three basal veins (rarely 5), agrophic veins absent or present; major secondary vein framework absent or semicraspedodromous distally; tertiary vein framework mixed percurrent; tooth spacing regular, teeth apically pointed, with indeterminate glandular tissue on the tooth apex.
Etymology: Named for K. Suessenguth in honor of his early work on the classification of Rhamnaceae.
Species: Suessenia grandensis Jud, Gandolfo, Iglesias & Wilf, sp. nov. Fig 3A–3F.
Holotype: MPEF-Pb 8553.
Repository: Museo Paleontológico Egidio Feruglio Paleobotany Collection (MPEF-Pb), Trelew City, Chubut, Argentina
Type Locality: Rancho Grande. Chubut, Argentina.
Stratigraphic position: Lower Salamanca Formation.
Age: Paleocene, early Danian, geomagnetic polarity chron C29n (65.58–64.86 Ma).
Etymology of specific epithet: from the Rancho Grande locality.
Species diagnosis: as for the genus Suessenia.
Description: Leaves simple, petiolate. Petiole stout, blade attachment marginal, laminar size microphyll. Laminar shape ovate to elliptic, with medial symmetry, length to width ratio 3:1 (7:3–4:1) (Fig 3A–3C). Apex acute, straight to acuminate, symmetrical (Fig 3B), base angle obtuse to acute, rounded to cuneate, insertion slightly asymmetrical (Fig 3A). Margin unlobed, serrate (Fig 3A–3F). Primary vein framework palmate acrodromous with three basal veins. Basal veins naked in some specimens (Fig 3C, at arrow). Major secondary veins not present, agrophic veins absent. Intercostal tertiary vein fabric (between the primary veins) mixed percurrent, angle of the percurrent tertiaries acute (Fig 3D). External tertiary veins supply the teeth (Fig 3F). Quaternary vein fabric irregular reticulate (Fig 3D). Tooth frequency decreasing distally, with one order, three teeth per cm (Fig 3A–3D). Sinus shape angular, tooth shape straight/retroflexed. Tooth apex pointed distally, with medial principal vein terminating at the tooth apex; each tooth with a gland on the apex (Fig 3E and 3F). Number of specimens examined: 31
The tree search using only floral characters and constrained by the topology of Hauenschild et al. , yielded two equally most-parsimonious trees: one with Notiantha deep in the ziziphoid clade and another sister to the extant Paliureae (Fig 4). The next tree search using the full 30 characters (from both flowers and leaves) resulted in five best trees. Three with Notiantha nested in the Paliureae, one with Notiantha sister to the Paliureae, and one with Notiantha sister to all ziziphoids except Gouanieae (S1 Fig). In all of the most-parsimonious trees obtained using the Hauenschild et al.  topology, the fossil-taxon was nested within the ziziphoid clade. The tree searches using the alternate topology reported by Onstein et al. yielded slightly differen results. The first analysis using only the floral characters for Notiantha resulted in eight most-parsimonious trees. One tree found Notiantha sister to the extant ampelozizyphoids, Ampelozizyphus and Bathiorhamnus (Fig 4), whereas all other trees placed Notiantha within the ziziphoid clade: either unplaced (e.g. sister to Ceanothus) or within the Paliureae (S2 Fig). Some trees in which the fossil is nested among the rhamnoids are only two steps longer than the optimal trees shown in (S2 Fig). The final tree search, using the full set of 30 floral and foliar characters, yielded four equally most-parsimonious trees. In one tree, the composite fossil-taxon is sister to the ampelozizyphoid clade, but in the other three trees, it is nested in the Paliureae (S3 Fig).
The alternate most parsimonious position in the ziziphoid clade for the fossil flowers is colored in dark green. A = Ampelozizypheae, B = Bathiorhamneae, V = Ventilagineae, R = Rhamneae, Po = Pomaderreae, C = Colletieae, Ph = Phyliceae, U = unplaced genera at tribal level, G = Gouanieae, Pa = Paliureae.
Comparison with extant and fossil plants
The flowers of Notiantha grandensis are readily assignable to Rhamnaceae because of their pentamerous structure, the obconical hypanthium with triangular keeled calyx lobes (sepals), clawed and cucullate petals, antepetalous stamens, and the floral disk [20,93,94]. Pentamerous flowers with antepetalous stamens are also found in Basellaceae Raf., Vitaceae Juss., Santalales Berchtold & J. Presl, and Gunneraceae Meisn. , but rhamnaceous flowers can be distinguished from among these when they have the combination of keeled sepals, clawed petals, filaments adnate to the petals, a hypanthium, or a fleshy floral disk.
As previously mentioned, there are eleven recognized tribes in Rhamnaceae, but several genera remain unplaced [26,27]. Many of the characters that have been identified as useful for distinguishing the tribes [21,27] are not preserved in the Patagonian fossils. The results of our phylogenetic analysis indicate that the fossil flowers are most like members of the ziziphoid clade, and the tribe Paliureae (Fig 4). The features supporting this relationship are the obconical floral cup, triangular to deltoid sepals each with a prominent keel, the floral disk adnate to the ovary filling the floral tube, the presence of short-clawed, cucullate petals with an apical notch, and a semi-inferior to superior ovary. By contrast, other tribes vary in the thickness and position of the floral disks, the shape of the hypanthium, and/or shape of the sepals. Notiantha differs from most extant members of Paliureae because the petals are apically emarginate and the floral disk is unlobed. In extant Paliureae, notched petals are rare, and they also occur outside of Paliureae in Condalia Cav., Karwinskia Zucc., Sageratia Brongn., Scutia (DC) Brongn., and Rhamnus L. [21,96–99]. The floral disk is often strongly lobed in extant Paliureae, with the sinuses associated with the insertion of the petal-stamen complex; however, it is possible that the size of the lobes in the floral disk changes during development, and, therefore, the absence of lobes in Notiantha may not be systematically informative. Based on the suite of characters in the fossil and the various most-parsimonious positions found in the phylogenetic analysis, it is likely that Notiantha belongs near the base of the ziziphoid clade.
The oldest known putative rhamnaceous flowers are the “Rose Creek flowers” from the mid-Cretaceous of Nebraska described by Basinger and Dilcher . Some authors consider these fossils to be the earliest evidence of Rhamnaceae because of the pentamerous, obhaplostemonous arrangement of the floral organs, short-clawed petals, a circular to pentagonal floral disk, a superior ovary, and distinctive pollen sculpture [100,101]. In contrast to crown-group Rhamnaceae, however, the Rose Creek flowers are much larger (20–40 mm across), lack a keel on the sepals, and the stamens are unlike those of extant Rhamnaceae. In the Rose Creek flowers, the filaments are stout, not adnate to the petals, and bear a large basifixed anther, whereas in most extant Rhamnaceae the filaments are slender, adnate to the petals, and bear minute, dorsifixed, and versatile anthers . Burge and Manchester  cautioned that petal-opposed stamens also occur in members of Vitales, the apparent sister to all other rosids , indicating that this condition might be expected in other early arising rosids. We further suggest, based on the presence of flowers with petal-opposed stamens and/or floral disks in several other groups such as Quillaja Molina (Quillajaceae, Fabales), Dirachma Schweinf. ex Balf.f. (Dirachmaceae, Rosales) Lepidobotrys Engl. (Lepidobotryaceae; Celastrales), and Santalales  that the condition of petal-opposed stamens only (obhaplostemony) has repeatedly derived from ancestors with two alternating whorls of stamens (obdiplostemony) in the Pentapetalae. Therefore, until the taxonomic position of the Rose Creek flowers can be confirmed, their placement within crown-group Rhamnaceae is doubtful.
More recently, Late Cretaceous rhamnaceous fossils (flowers, leaves and seeds) were described from the Cerro del Pueblo Formation in Mexico  and the Guaduas Formation in Colombia . Among these fossils are the flowers described as Coahuilanthus belindae Calvillo-Canadell et Cevallos-Ferriz from El Almácigo locality (Cerro del Pueblo Formation, late Campanian) in General Cepeda County, Coahuila, Mexico (Table 2). Coahuilanthus are easily distinguished from Notiantha by the petals, which are much shorter than the calyx, and spatulate rather than cucullate as in Notiantha. Furthermore, Coahuilanthus flowers have a campanulate, rather than obconic, hypanthium and a 10-lobed floral disk. So far, Coahuilanthus is the earliest reliable fossil evidence of Rhamnaceae.
Several genera have been established based on fossilized rhamnaceous flowers from Cenozoic deposits as well, but Notiantha may be distinguished from each of these by features of the corolla and the hypanthium (Table 2). The flowers described as “Solanites” pusillus Berry from the Eocene of Tennessee, USA  were recently recognized as Rhamnaceae by Millán and Crepet . They have a campanulate floral cup and obovate petals each with a rounded apex, features that distinguish “S.” pusillus from the Patagonian fossils. Comparison of Notiantha with the flowers of Nahinda axamilpensis Calvillo-Canadell et Cevallos-Ferriz, from the Oligocene of Mexico, reveals that the petals are much shorter in N. axamilpensis . Chambers and Poinar described two rhamnaceous flowers from Dominican Amber [104,105], Distigouania irregularis Chambers et Poinar and Comopellis presbya Chambers et Poinar. They compared D. irregularis with the extant Gouania Jacq. and noted the unusual combination of sepaloid petals with a more typical cucullate petal in the same flower. Notiantha can easily be distinguished from these two taxa. D. irregularis is considered a staminate flower, whereas Notiantha is perfect. C. presbya has a wider floral cup than N. grandensis, cucullate petals that tightly enfold the stamens, and enlarged appendages that radiate from the floral disk. By contrast, the petals of Notiantha are clearly short-clawed and do not enfold the anther, and there is no evidence of any kind of enlarged appendages radiating from the floral disk. Clearly, the Patagonian fossil flowers are different from previously described rhamnaceous fossil flowers, and consequently the erection of a new genus and species is warranted.
Some members of Rhamnaceae produce morphologically distinctive leaves sometimes referred to as rhamnoid- or ziziphoid-type foliage. Leaves of the rhamnoid type are simple, entire, and pinnate, with eucamptodromous secondary veins and closely spaced opposite-percurrent tertiary veins that are nearly perpendicular to the midvein [28,106]. By contrast, leaves of the ziziphoid-type are simple, and palmate with three acrodromous primary veins, mixed alternate-percurrent epimedial tertiary veins, and usually a serrate margin with apically oriented, glandular teeth. Major secondary veins, if present, occur in the distal portion of the leaf blade [51,52]. The rhamnoid and ziziphoid leaf types are distinctive end-members of a range of leaf-types found in Rhamnaceae [28,106,107]. ‘Ziziphoid’ leaves are typical of the Paliureae and some other genera in the ziziphoid clade (e.g. Ceanothus, Colubrina, Crumenaria Mart.), as well as the ampelozizyphoid clade (e.g. Bathiorhamnus).
Many of the dispersed rhamnaceous fossil leaves have been assigned to the modern genera Ziziphus, Paliurus, or Ceanothus; however, these extant genera cannot be reliably distinguished based on leaf architecture alone , suggesting that the assignment of the fossils to them is dubious. Dispersed leaves that have Rhamnaceae-like morphology but do not fit into the rhamnoid or ziziphoid leaf types are common in the fossil record; however, they are not necessarily identifiable as Rhamnaceae based on venation and margin type alone because genera of other families converge on similar morphology [38,106,108–110]. Even in those cases where an affinity with Rhamnaceae is or could be confirmed, previous assignments to extant genera should be re-evaluated [38,106,107]. Some of the fossil species conforming to the ziziphoid leaf type that should be re-described may be transferred to Suessenia.
A thorough review of all fossil “rhamnaceous” leaves is beyond the scope of this work; however, a detailed comparison of Sussenia with fossil rhamnaceous leaves reported from South America was performed. The first report of fossil leaves attributed to Rhamnaceae from South America include Rhamnidium patagonicum Berry and R. preglabrum Berry in the Eocene Laguna del Hunco flora [111–113]. These are closer to the rhamnoid leaf type and are unlike S. grandensis. Later, Ziziphus chubutensis Berry, was described based on material collected from the Palacio de los Loros locality in the Salamanca Fm. [15,62,114]. Z. chubutensis leaves are broadly consistent with those of Paliureae becuase they have three strong basal veins that appear actinodromous (nearly acrodromous), a serrate margin, and glandular teeth. Later, Iglesias et al.  suggested that Banarophyllum ovatum Berry, also from the Salamanca Fm. and originally allied with Flacourtiaceae, may be a junior synonym of Z. chubutensis [15,62]. Troncoso  reported the occurrence of a single ziziphoid leaf from the Eocene of Chile identified as Ziziphus sp.; unfortunately, the fossil is poorly preserved. The base and much of the margin of this specimen are unknown, and therefore this occurrence should be treated with caution. Finally, Correa et al.  reported the occurrence of Berhamniphyllum from the Late Cretaceous of Colombia, but these also conform to the “rhamnoid” leaf type. Suessenia leaves are readily distinguished from those of Ziziphus chubutensis because they consistently lack major secondary veins in the distal portion of the blade and because the apex is very acute to attenuate, rather than rounded and obtuse. They are also easily distinguished from the specimen Berry identified as B. ovatum because they lack major secondary veins, and the tertiary veins are often alternate percurrent, not opposite percurrent. Thus, we consider Suessenia distinct from previously reported rhamnaceous leaves from South America and the oldest reliable occurrence of the ziziphoid leaf type.
Rhamnaceae are distributed throughout tropical and temperate environments worldwide [21,116], but highest diversity is associated with seasonally dry Mediterranean-type environments [29,56]. The broad distribution of the family hindered early efforts to draw conclusions about their biogeographic history . Gentry  proposed a Laurasian origin for the family and subsequent expansion into the Southern Hemisphere; however, recent work supports an alternate hypothesis. Richardson et al. and Onstein et al. showed that many of the groups associated with tropical and subtropical forests are early-divergent lineages within Rhamnaceae [26,29,53,56]. Richardson et al.  suggested a Gondwanan origin for the family but did not specify the forest type, and Onstein et al. [29,56] emphasized the tropical rainforest aspect of the likely ancestral habitat. The occurrence of fossil Rhamnaceae in the Neotropics during the Late Cretaceous on either side of the Central American Seaway [28,31] is suggestive of an “out of the tropics” scenario for the evolution of the crown-group Rhamnaceae rather than a traditional “Gondwanan” or “Laurasian” origin at mid- or high-latitudes. This hypothesis is consistent with the distribution of several of the extant representatives of the ampelozizyphoids, which are found in Cuba, northern tropical South America, east Africa, and Madagascar, and the primarily Neogene radiations of more derived rhamnoid and ziziphoid lineages in Mediterranean habitats worldwide [23,29,56,87].
There are 16 extant genera of Rhamnaceae native to the southern cone of South America (Chile, Argentina, Paraguay, Uruguay, and southern Brazil), and one of them is endemic to Chile [118–120]. Much of the species richness in that region, particularly in the Colletieae Reissek ex Endl. , is found in the Mediterranean-type climate of Chile and western Argentina, whereas other lineages, including Sarcomphalus (formerly new-world Ziziphus), Hovenia (introduced), Colubrina, and Gouania Jacq. are found in the subtropical forests of northern Argentina [118,119].
Southern Chubut Province (Argentina), where the fossils were collected, has a semi-arid to cold-steppe ecoregion . Today, in the San Jorge Basin, the mean annual temperature is 11.5°C and mean annual precipitation is 16.4 cm yr-1 . Condalia, Colletia Comm. Ex Juss., Discaria Hook., and Trevoa Miers can be found in the region today (pers. obs.). By contrast, paleoclimate estimates for the Salamanca Fm. biota suggest subtropical lowland environment with a mean annual temperature of ~13–14°C, and mean annual rainfall of 115–124 cm yr-1 based on foliar physiognomy  and the presence of thermophilic groups (palms, podocarps, and alligatorids) . This reconstructed climate is similar to the subtropical forests of northern Argentina where Sarcomphalus, Hovenia, and Colubrina grow today .
Most fossils assigned to Rhamnaceae have been collected from Eocene and younger deposits across the Northern Hemisphere (Fig 1; Table 1). Although the fossils described by Correa et al.  are from South America, they are not technically from the Southern Hemisphere. The only previous reports of rhamnaceous fossils from the Southern Hemisphere were based on dispersed leaves [62,111,115,124,125] or pollen [126–130]. Two of these pollen occurrences are from Antarctica, the only continent where Rhamnaceae does not grow today (Fig 1). Fossil wood [131,132] and fruits [133,134] attributed to Rhamnacae have been reported from the Deccan Intertrappean beds of India, which was in the Southern Hemisphere or straddled the equator for much of the Late Cretaceous and Paleogene; however, Guleria  and Prakash  found that these records are unreliable. The fossils either do not preserve some of the features that are necessary to confirm or reject the rhamnaceous affinities, or they show closer affinities with other families. The remarkably sparse fossil record of Rhamnaceae from the Southern Hemisphere contrasts with the rich record in the Northern Hemisphere. Traditionally, this has been thought to reflect a Laurasian origin for the family and subsequent expansion into Gondwanan landmasses ; however, a simpler explanation may be that geographical sampling bias drives this pattern. Recent work has demonstrated the potential for new discoveries in the Southern Hemisphere to improve our understanding of the history of various widespread (or formerly widespread) groups [28,138–142].
The fossils described here are, to our knowledge, the first early Danian flowers known from the Southern Hemisphere. They are also the southernmost fossil occurrence of Rhamnaceae flowers and the only unequivocal megafossil occurrence of the family in the Southern Hemisphere. Based on the results of our phylogenetic analyses together with all available evidence, we argue that the discovery of Notiantha provides a reliable minimum age of 66 Million years for the node that unites the extant ziziphoids; the most conservative approach would be to apply a minimum age of 66 Million years for the node that unites the ziziphoid and ampeloziziphoid clade, i.e. the base of the crown-group. The Late Cretaceous occurrences of Rhamnaceae from the Neotropics and the tropical distribution of several extant, early-diverging lineages of the family indicates that the initial diversification of the family took place in warm and wet tropical to subtropical forests, and the family later spread to temperate and Mediterranean biomes . The discovery of Notiantha (flowers) together with Suessenia (ziziphoid leaves) from the Salamanca Formation confirms that Rhamnaceae reached southern South America by the early Paleocene and raises the possibility for southern dispersal routes via Antarctica and subsequent vicariance [143–147] to help explain biogeographic patterns of Rhamnaceae .
S1 Table. Comparative material of extant Rhamnaceae.
List of examined comparative material of extant Rhamnaceae. US: United States National Herbarium; NCLC-H: National Cleared Leaf Collection-Hickey; FLAS: University of Florida Herbarium; BH: Bailey Hortorium, Cornell University.
S1 Fig. Hauenschild et al. topology including floral and foliar characters.
Phylogeny including One of five equally most parsimonious trees based on floral and foliar characters and the topology of Hauenschild et al.  showing the position of Notiantha sister to the extant Paliureae [Hovenia+Sarcomphalus+Paliurus+Ziziphus] at arrow. The four alternate most parsimonious positions for the fossil flowers in the ziziphoid clade are colored in dark green. A = Ampelozizypheae, B = Bathiorhamneae, V = Ventilagineae, R = Rhamneae, Po = Pomaderreae, C = Colletieae, Ph = Phyliceae, U = unplaced genera at tribal level, G = Gouanieae, Pa = Paliureae.
S2 Fig. Onstein et al. topology including floral characters.
One of eight equally most parsimonious trees based on floral characters the topology of Onstein et al.  showing the position of Notiantha nested in Paliureae sister to [Hovenia+Paliurus+Ziziphus] at arrow. The seven alternate most parsimonious positions for the fossil flowers are colored in dark green. A = Ampelozizypheae, B = Bathiorhamneae, V = Ventilagineae, R = Rhamneae, Po = Pomaderreae, C = Colletieae, Ph = Phyliceae, U = unplaced genera at tribal level, G = Gouanieae, Pa = Paliureae. This result was obtained using only the first 25 floral characters and is therefore conservative.
S3 Fig. Onstein et al. topology including floral and foliar characters.
One of four equally most parsimonious trees based on floral and foliar characters and the topology of Onstein et al.  showing the position of Notiantha nested in Paliureae sister to [Hovenia+Paliurus+Ziziphus] at arrow. The three alternate most parsimonious positions for the fossil flowers are colored in dark green. A = Ampelozizypheae, B = Bathiorhamneae, V = Ventilagineae, R = Rhamneae, Po = Pomaderreae, C = Colletieae, Ph = Phyliceae, U = unplaced genera at tribal level, G = Gouanieae, Pa = Paliureae.
The authors thank M. Caffa, L. Canessa, K. Johnson, P. Puerta, A. Reznicek, J. Svitko, and many others for assistance in the field and laboratory work. We also thank the Secretaría de Cultura de la Provincia de Chubut, and E. Thomas for facilitating land access. Funding supporting this work came from the National Science Foundation (grants DEB-1556136, DEB-0918932, DEB-1556666, DEB-0919071, and DEB-0345750) and the Fulbright Foundation (MAG).
- Conceptualization: MAG PW.
- Data curation: NAJ AI.
- Formal analysis: NAJ.
- Funding acquisition: MAG PW.
- Investigation: NAJ.
- Methodology: NAJ.
- Project administration: MAG NAJ.
- Resources: MAG AI PW.
- Software: NAJ.
- Supervision: MAG.
- Validation: NAJ MAG PW.
- Visualization: NAJ MAG PW AI.
- Writing – original draft: NAJ.
- Writing – review & editing: NAJ MAG PW AI.
- 1. Gelfo JN, Pascual R. Peligrotherium tropicalis (Mammalia, Dryolestida) from the early Paleocene of Patagonia, a survival from a Mesozoic Gondwanan radiation. Geodiversitas. 2001;23(3):369–379.
- 2. Petriella BTP, Archangelsky S. Vegetación y ambiente en el Paleoceno de Chubut. Actas Congr Argent Paleontol Bioestratigrafía. 1975;2:257–270.
- 3. Archangelsky S, Zamaloa M del C. Nuevas descripciones palinológicas de las formaciones Salamanca y Bororó, Paleoceno de Chubut (República Argentina). Ameghiniana. 1986;23(1–2):35–46.
- 4. Pascual R, Archer M, Jaureguizar EO, Prado JL, Godthelp H, Hand SJ. First discovery of monotremes in South America. Nature. 1992;356(6371):704–706.
- 5. Bonaparte JF, Van Valen LM, Kramartz A. La fauna local de Punta Peligro, Paleoceno inferior, de la provincia del Chubut, Patagonia, Argentina. Evol Monogr. 1993;14:1–61.
- 6. Bonaparte JF, Morales J. Un primitivo Notonychopidae (litopterna) del Paleoceno inferior de Punta Peligro, Chubut, Argentina. Estud Geológicos. 1997;53(5–6):263–274.
- 7. Forasiepi AM, Martinelli AG. Femur of a monotreme (Mammalia, Monotremata) from the Early Paleocene Salamanca Formation of Patagonia, Argentina. Ameghiniana. 2003;40(4):625–630.
- 8. Brea M, Matheos S, Zamuner A, Ganuza D. Análisis de los anillos de crecimiento del bosque fósil de Víctor Szlápelis, Terciario inferior del Chubut, Argentina. Ameghiniana. 2005;42(2):407–418.
- 9. Brea M, Zamuner AB, Matheos SD, Iglesias A, Zucol AF. Fossil wood of the Mimosoideae from the early Paleocene of Patagonia, Argentina. Alcheringa. 2008;32(4):427–441.
- 10. Matheos SD, Brea M, Zucol AF, Prámparo M, Raigemborn MS, Iglesias A, et al. Análisis paleoambiental de las sedimentitas del Daniano del sector sur de los Lagos Musters y Colhue Huapi (Chubut, Argentina). In: Actas XVI Congreso Geológico Argentino (La Plata). 2005. p. 83–90.
- 11. Gelfo JN. The “condylarth” Raulvaccia peligrensis (Mammalia: Didolodontidae) from the Paleocene of Patagonia, Argentina. J Vertebr Paleontol. 2007;27(3):651–660.
- 12. Gelfo JN, López GM, Bond M. A new Xenungulata (Mammalia) from the Paleocene of Patagonia, Argentina. J Paleontol. 2008;82(2):329–335.
- 13. Gurovich Y. Additional specimens of sudamericid (Gondwanatheria) mammals from the early Paleocene of Argentina. Palaeontology. 2008;51(5):1069–1089.
- 14. Pascual R, Goin FJ, Balarino L, DE US. New data on the Paleocene monotreme Monotrematum sudamericanum, and the convergent evolution of triangulate molars. Acta Palaeontol Pol. 2002;47(3):487–492.
- 15. Iglesias A, Wilf P, Johnson KR, Zamuner AB, Cúneo NR, Matheos SD, et al. A Paleocene lowland macroflora from Patagonia reveals significantly greater richness than North American analogs. Geology. 2007;35(10):947–950.
- 16. Futey MK, Gandolfo MA, Zamaloa MC, Cúneo R, Cladera G. Arecaceae fossil fruits from the Paleocene of Patagonia, Argentina. Bot Rev. 2012;78(3):205–234.
- 17. Clyde WC, Wilf P, Iglesias A, Slingerland RL, Barnum T, Bijl PK, et al. New age constraints for the Salamanca Formation and lower Río Chico Group in the western San Jorge Basin, Patagonia, Argentina: Implications for Cretaceous-Paleogene extinction recovery and land mammal age correlations. Geol Soc Am Bull. 2014 Mar 1;126(3–4):289–306.
- 18. Comer EE, Slingerland RL, Krause JM, Iglesias A, Clyde WC, Raigemborn MS, et al. Sedimentary facies and depostional evirionments of diverse early Paleocene floras, north-central San Jorge Basin, Patagonia, Argentina. Palaios. 2015;30(7):553–573.
- 19. Donovan MP, Iglesias A, Wilf P, Labandeira CC, Cúneo NR. Rapid recovery of Patagonian plant–insect associations after the end-Cretaceous extinction. Nat Ecol Evol. 2016 Nov 7;1:0012.
- 20. Brown R. General remarks, geographical and systematical, on the botany of Terra Australis. London; 1814.
- 21. Medan D, Schirarend C. Rhamnaceae. In: Flowering Plants Dicotyledons. Springer; 2004. p. 320–338.
- 22. Hauenschild F, Favre A, Salazar GA, Muellner-Riehl AN. Analysis of the cosmopolitan buckthorn genera Frangula and Rhamnus s.l. supports the description of a new genus, Ventia. Taxon. 2016;65(1):65–78.
- 23. Hauenschild F, Matuszak S, Muellner-Riehl AN, Favre A. Phylogenetic relationships within the cosmopolitan buckthorn family (Rhamnaceae) support the resurrection of Sarcomphalus and the description of Pseudoziziphus gen. nov. Taxon. 2016;65(1):47–64.
- 24. Bentham G, Hooker JD. Genera plantarum: ad exemplaria imprimis in Herberiis Kewensibus servata definita. London: Londini, Reeve & Co.; 1862. 465 p.
- 25. Suessenguth K. Rhamnaceae, Vitaceae, Leeaceae. Berlin: Duncker & Humblot; 1953. 398 p. (Natürlichen Pflanzenfamilien, 2 Aufl., Bd. 20d.).
- 26. Richardson JE, Fay MF, Cronk QC, Bowman D, Chase MW. A phylogenetic analysis of Rhamnaceae using rbcL and trnL-F plastid DNA sequences. Am J Bot. 2000;87(9):1309–1324. pmid:10991902
- 27. Richardson JE, Fay MF, Cronk QCB, Chase MW. A revision of the tribal classification of Rhamnaceae. Kew Bull. 2000;311–340.
- 28. Correa E, Jaramillo C, Manchester S, Gutierrez M. A fruit and leaves of Rhamnaceous affinities from the late Cretaceous (Maastrichtian) of Colombia. Am J Bot. 2010;97(1):71–79. pmid:21622368
- 29. Onstein RE, Carter RJ, Xing Y, Richardson JE, Linder HP. Do Mediterranean-type ecosystems have a common history?—Insights from the Buckthorn family (Rhamnaceae). Evolution. 2015;69(3):756–771. pmid:25611684
- 30. Millan M, Crepet W. The fossil record of the Solanaceae revisited and revised—The fossil record of Rhamnaceae enhanced. Bot Rev. 2014;80(2):73–106.
- 31. Calvillo-Canadell L, Cevallos-Ferriz SR. Reproductive structures of Rhamnaceae from the Cerro del Pueblo (Late Cretaceous, Coahuila) and Coatzingo (Oligocene, Puebla) Formations, Mexico. Am J Bot. 2007;94(10):1658–1669. pmid:21636362
- 32. Miki S. On the Pleistocene flora in Prov. Yamashiro Jpn Kyoto-Fu Shiseki-Meisho Tennenkinenbutu Chosa-Hokoku. 1933;14:1–27.
- 33. Miki S. Plant fossils from the Stegodon Beds and the Elephas Beds near Akashi. Jpn J Bot. 1937;8(4):303–341.
- 34. Bŭžek C. Tertiary flora of the Northern Part of the Petipsy Area—(North-Bohemian Basin). Rozpr Ustrĕdního Úst Geol. 1971;36:1–118.
- 35. Zhilin SG. History of the development of the temperate forest flora in Kazakhstan, USSR from the Oligocene to the early Miocene. Bot Rev. 1989;55(4):205–330.
- 36. Tsukagoshi M, Suzuki K. On the late Miocene Cinnamomum and Paliurus from the lower part of the Takamine Formation, western mountainous region of the Yonezawa Basin, northeast Honshu, Japan. Bull Misunami Foss Mus. 1990;17:71–78.
- 37. Meyer HW, Manchester SR. Oligocene Bridge Creek flora of the John Day Formation, Oregon. Berkeley: University of California Press; 1997. (University of California publications in geological sciences; vol. 141).
- 38. Burge DO, Manchester SR. Fruit morphology, fossil history, and biogeography of Paliurus (Rhamnaceae). Int J Plant Sci. 2008;169(8):1066–1085.
- 39. Li X, Wang H, Leng Q, Xiao L, Guo J, He W. Paliurus (Paliureae, Rhamnaceae) from the Miocene of East China and its macrofossil-based phylogenetic and phytogeographical history. Acta Geol Sin Engl Ed. 2014;88(5):1364–1377.
- 40. Dong J-L, Sun B-N, Ma F-J, Wang Q-J, Jin P-H, Wang W-J, et al. Paliurus Fruits from the Oligocene of South China and Their Phytogeographic Implications. PLoS ONE. 2015;10(11):e0140653. pmid:26536607
- 41. Han M, Chen G, Shi X, Jin J. Earliest fossil fruit record of the genus Paliurus (Rhamnaceae) in Eastern Asia. Sci China Earth Sci. 2016 Jan 26;59(4):824–830.
- 42. Collinson ME, Manchester SR, Wilde V. Fossil fruits and seeds of the Middle Eocene Messel biota, Germany. Abh Senckenberg Ges Für Naturforschung. 2012;570:1–251.
- 43. Liu K-N, Xie S-P, Manchester SR, Wang Y-F, Shao Y, Li B-K. Samaras of Ventilago (Rhamnaceae) from the upper Miocene of Lincang, Yunnan, China and their phytogeographic implications. J Syst Evol. 2015;53(3):252–258.
- 44. Watari S. Dicotyledonous woods from the Miocene along the Japan-Sea side of Honsyu. J Fac Sci Univ Tokyo Sec III Bot. 1952;6:97–134.
- 45. Suzuki M. Some fossil woods from the Palaeogene of Northern Kyushu, II. Bot Mag Shokubutsu-Gaku-Zasshi. 1982;95(3):281–294.
- 46. Wheeler EA, Meyer HW. A new (Hovenia) and an old (Chadronoxylon) fossil wood from the Late Eocene Florissant formation, Colorado, USA. IAWA J. 2012;33(3):309–318.
- 47. Mason HL. Distributional history and fossil record of Ceanothus. Santa Barbara: Santa Barbara Botanic Garden; 1942. unpaginated.
- 48. Nobs MA. Experimental studies on species relationships in Ceanothus. Washington: Carnegie Institution of Washington; 1963. 94 p. (Carnegie Institution of Washington publication; vol. 623).
- 49. Axelrod DI. Miocene floras from the Middlegate Basin, west-central Nevada. Univ of California Press; 1985. 279 p. (University of California publications in geological sciences; vol. 129).
- 50. Axelrod DI. The Miocene Purple Mountain flora of western Nevada. Univ of California Press; 1995. 62 p. (University of California publications in geological sciences; vol. 139).
- 51. MacGinitie HD. Fossil plants of the Florissant beds, Colorado. Carnegie Institution of Washington; 1953. 198 p. (Carnegie Institution of Washington Publication; vol. 599).
- 52. Manchester SR. Update on the megafossil flora of Florissant, Colorado. Denver Mus Nat Sci. 2001;4:137–161.
- 53. Richardson JE, Chatrou LW, Mols JB, Erkens RHJ, Pirie MD. Historical biogeography of two cosmopolitan families of flowering plants: Annonaceae and Rhamnaceae. Philos Trans R Soc Lond B Biol Sci. 2004;359(1450):1495–1508. pmid:15519968
- 54. Burge DO, Erwin DM, Islam MB, Kellermann J, Kembel SW, Wilken DH, et al. Diversification of Ceanothus (Rhamnaceae) in the California Floristic Province. Int J Plant Sci. 2011;172(9):1137–1164.
- 55. Gentry AH. Neotropical floristic diversity: Phytogeographical connections between Central and South America, Pleistocene climatic fluctuations, or an accident of the Andean Orogeny? Ann Mo Bot Gard. 1982;69(3):557–593.
- 56. Onstein RE, Linder HP. Beyond climate: convergence in fast evolving sclerophylls in Cape and Australian Rhamnaceae predates the Mediterranean climate. J Ecol. 2016;104(3):665–677.
- 57. Wikström N, Savolainen V, Chase MW. Evolution of the angiosperms: calibrating the family tree. Proc R Soc Lond B Biol Sci. 2001;268(1482):2211–2220.
- 58. Raigemborn MS, Krause JM, Bellosi E, Matheos SD. Redefinición estratigráfica del Grupo Río Chico (Paleógeno Inferior), en el norte de la cuenca del golfo San Jorge, Chubut. Rev Asoc Geológica Argent. 2010;67(2):239–256.
- 59. Andreis RR. Estudio estratigráfico y paleoambiental de las sedimentitas Terciarias entre Pico Salamanca y Bahía Bustamante, Provincia de Chubut, República Argentina. Rev Asoc Geológica Argent. 1975;30:85–103.
- 60. Matheos SD, Brea M, Gamuza D, Zamuner A. Sedimentología y paleoecología del Terciario inferior en el sur de la provincia del Chubut, República Argentina. Rev Asoc Argent Sedimentol. 2001;8(1):93–104.
- 61. Legarreta L, Uliana MA. Asociaciones de fósiles y hiatos en el Supracretácico-Neógeno de Patagonia: una perspectiva estratigráfico-secuencial. Ameghiniana. 1994;31(3):257–281.
- 62. Berry EW. A Paleocene flora from Patagonia. Johns Hopkins Univ Stud Geol. 1937;12:33–50.
- 63. Barreda VD, Cúneo NR, Wilf P, Currano ED, Scasso RA, Brinkhuis H. Cretaceous/Paleogene floral turnover in Patagonia: drop in diversity, low extinction, and a Classopollis spike. PLoS ONE. 2012;7(12):e52455. pmid:23285049
- 64. Archangelsky S. Palinología del Paleoceno de Chubut. I. Descripciones sistemáticas. Ameghiniana. 1973;10(4):339–399.
- 65. Zucol A. F.; Brea M. y Matheos S.. Estudio preliminar de microrestos silíceos de la Formación Salamanca (Paleoceno inferior), Chubut, Argentina. En: Zucol A. F.; Osterrieth M. y Brea M. (Eds.), Fitolitos: Estado actual de sus conocimientos en América del Sur. Mar del Plata. 2008;149–156. Universidad Nacional de Mar del Plata. EUDEM.
- 66. Frenguelli J. El banco verde de paso Niemann del río Chico en el Chubut y sus Diatomeas. Buenos Aires: Casa Ed. Coni; 1936. 65 p.
- 67. Camacho HH. Some Upper Cretaceous foraminifera from Argentina. Contrib Cushman Found Foraminifer Res. 1954;5(1):31–35.
- 68. Camacho HH. Las transgresiones del Cretácico superior y Terciario de la Argentina. Rev Asoc Geológica Argent. 1967;22(4):253–280.
- 69. Méndez I. Foraminíferos, edad y correlación estratigráfica del Salamanquense de Punta Peligro (45 30′ S; 67 11′ W), provincia del Chubut. Rev Asoc Geológica Argent. 1966;21(2):127–157.
- 70. Masiuk V. Estratigrafia del Rocanense del Puesto P. Alvarez: Curso inferior del Río Chico, Prov. del Chubut. Revista Museo de La Plata n.s. Paleontología 1967;5:197–258.
- 71. Bertels A. Bioestratigrafía del Paleógeno en la República Argentina. Rev Esp Micropaleontol. 1975;7(3):429–450.
- 72. Feldmann RM, Rodriguez MF, Martinez GA, Aguirre-Urreta M. Costacopluma salamanca New Species (Decapoda, Retroplumidae) from the Salamanca Formation (Danian) of Patagonia, Argentina. J Paleontol. 1997;71(1):125–30.
- 73. Chebli G, Serraiotto A. Nuevas localidades del Paleoceno marino en la región central de la Provincia del Chubut. Rev Asoc Geológica Argent. 1974;29(3):311–318.
- 74. Andreis RR. Geología del área de Cañadón Hondo, Dpto Escalante, Provincia de Chubut, República Argentina. Obra Centen Mus Plata. 1977;4:77–102.
- 75. Parma SG, Casadío S. Upper Cretaceous–Paleocene echinoids from Northern Patagonia, Argentina. J Paleontol. 2005 Nov 1;79(6):1072–1087.
- 76. Bona P, De La Fuente MS. Phylogenetic and paleobiogeographic implications of Yaminuechelys maior (Staesche, 1929) new comb., a large long-necked chelid turtle from the early Paleocene of Patagonia, Argentina. J Vertebr Paleontol. 2005;25(3):569–582.
- 77. Bona P. Una nueva especie de Eocaiman Simpson (Crocodylia, Alligatoridae) del Paleoceno Inferior de Patagonia. Ameghiniana. 2012;44(2):435–445.
- 78. Sterli J, de la Fuente MS. New evidence from the Palaeocene of Patagonia (Argentina) on the evolution and palaeo-biogeography of Meiolaniformes (Testudinata, new taxon name). J Syst Palaeontol. 2013;11(7):835–852.
- 79. Gelfo JN, Ortiz-Jaureguizar E, Rougier GW. New remains and species of the “condylarth”genus Escribania (Mammalia: Didolodontidae) from the Palaeocene of Patagonia, Argentina. Earth Environ Sci Trans R Soc Edinb. 2007;98(2):127–138.
- 80. Gradstein FM, Ogg JG, Schmitz M, Ogg G, editors. The Geologic Time Scale 2012. 1st ed. Elsevier; 2012. 1176 p.
- 81. Palazzesi L, Barreda V. Major vegetation trends in the Tertiary of Patagonia (Argentina): A qualitative paleoclimatic approach based on palynological evidence. Flora—Morphol Distrib Funct Ecol Plants. 2007;202(4):328–337.
- 82. Peppe DJ, Royer DL, Cariglino B, Oliver SY, Newman S, Leight E, et al. Sensitivity of leaf size and shape to climate: global patterns and paleoclimatic applications. New Phytol. 2011 May;190(3):724–739. pmid:21294735
- 83. Hinojosa LF, Pérez F, Gaxiola A, Sandoval I. Historical and phylogenetic constraints on the incidence of entire leaf margins: insights from a new South American model. Glob Ecol Biogeogr. 2011 May 1;20(3):380–390.
- 84. Ellis B, Daly DC, Hickey LJ, Mitchell JD, Johnson KR, Wilf P, et al. Manual of Leaf Architecture. First Edition. Comstock Publishing Associates, Cornell University Press, Ithaca, New York, USA.; 2009. 200 p.
- 85. Calvillo-Canadell L. Determinación taxonómica de estructuras reproductivas y vegetativas de plantas fósiles de Tepexi de Rodríguez, Puebla. Unpubl MS Thesis Univ Nac Autónoma Mex. 2000;
- 86. Aagesen L. Phylogeny of the tribe Colletieae, Rhamnaceae. Bot J Linn Soc. 1999;131(1):1–43.
- 87. Islam MB, Simmons MP. A thorny dilemma: testing alternative intrageneric classifications within Ziziphus (Rhamnaceae). Syst Bot. 2006;31(4):826–842.
- 88. Meier W, Berry PE. Ampelozizyphus guaquirensis (Rhamnaceae), a new tree species endemic to the Venezuelan Coastal Cordillera. Brittonia. 2008;60(2):131–135.
- 89. Callmander MW, Phillipson PB, Buerki S. Révision du genre Bathiorhamnus Capuron (Rhamnaceae) endémique de Madagascar. Adansonia. 2008;30(1):151–170. pmid:21866216
- 90. Springer MS, Teeling EC, Madsen O, Stanhope MJ, Jong WW. Integrated fossil and molecular data reconstruct bat echolocation. Proc Natl Acad Sci. 2001;98(11):6241–6246. pmid:11353869
- 91. Goloboff PA. Tree searches under Sankoff parsimony. Cladistics. 1998;14(3):229–237.
- 92. Nixon KC. The Parsimony Ratchet, a New Method for Rapid Parsimony Analysis. Cladistics. 1999 Dec 1;15(4):407–414.
- 93. Nowicke JW. Flora of Panama. VI. Family 111. Rhamnaceae. Woodson RE, Schery RW, Nowicke JW, editors. Nnals Mo Bot Gard. 1971;58(3):267–283.
- 94. Cronquist A. An integrated system of classification of flowering plants. Columbia University Press; 1981. 1262 p.
- 95. Lacroix C, Sattler R. Phyllotaxis theories and tepal-stamen superposition in Basella rubra. Am J Bot. 1988;906–917.
- 96. Johnston MC. Revision of Scutia (Rhamnaceae). Bull Torrey Bot Club. 1974;101(2):64–72.
- 97. Pusalkar PK, Singh DK. Sageretia santapaui sp. nov. and S. devendrae sp. nov. (Rhamnaceae) from western Himalaya, India. Nord J Bot. 2010 Feb;28(1):49–53.
- 98. Henrickson J. A new species of Condalia (Rhamnaceae) from Sonora, Mexico. Londellia. 2003;6:138–143.
- 99. Zuccarini JG. Plantarum novarum vel minus cognitarum, quae in horto botanico herbarioque regio Monacensi servantur/descripsit Jos. Gerh. Zuccarini. München: Königlich Bayerische Akademie der Wissenschaften; 1832. 431 p.
- 100. Basinger JF, Dilcher DL. Ancient bisexual flowers. Science. 1984;224(4648):511–513. pmid:17753776
- 101. Crepet WL, Nixon KC, Gandolfo MA. Fossil evidence and phylogeny: the age of major angiosperm clades based on mesofossil and macrofossil evidence from Cretaceous deposits. Am J Bot. 2004;91(10):1666–1682. pmid:21652316
- 102. Jansen RK, Kaittanis C, Saski C, Lee S-B, Tomkins J, Alverson AJ, et al. Phylogenetic analyses of Vitis (Vitaceae) based on complete chloroplast genome sequences: effects of taxon sampling and phylogenetic methods on resolving relationships among rosids. BMC Evol Biol. 2006;6(32) 14p.
- 103. Berry EW. Revision of the Lower Eocene Wilcox Flora of the Southeastern States: With Descriptions of New Species, Chiefly from Tennessee and Kentucky. U.S. Government Printing Office; 1930. 260 p.
- 104. Chambers K, Poinar GO Jr. Distigouania irregularis gen. et sp. nov (Rhamnaceae) in mid-Tertiary amber from the Dominican Republic. J Bot Res Inst Tex. 2014;8:551–557.
- 105. Chambers KL, Poinar GO Jr. Comopellis presbya gen. et sp. nov. (Rhamnaceae) in mid-Tertiary amber from the Dominican Republic. J Bot Res Inst Tex. 2015;9(2):361–367.
- 106. Jones JH, Dilcher DL. Investigations of angiosperms from the Eocene of North America: Rhamnus marginatus (Rhamnaceae) reexamined. Am J Bot. 1980;959–967.
- 107. Knobloch E, Kvaček Z. Miozäne Blätterfloren vom Westrand der Böhmischen Masse. Academia; 1976. 131 p.
- 108. Brown RW. Fossil leaves, fruits, and seeds of Cercidiphyllum. J Paleontol. 1939;13(5):485–499.
- 109. Brown RW. Paleocene Flora of the Rocky Mountains and Great Plains. U.S. Government Printing Office; 1962. 276 p.
- 110. Manchester SR. Revisions to Roland Brown’s North American Paleocene Flora. Acta Musei Natl Pragae Ser B—Hist Nat. 2014;70(3/4):153–210.
- 111. Berry EW. A Miocene flora from Patagonia. Johns Hopkins Univ Stud Geol. 1925;6:183–251.
- 112. Wilf P, Cúneo NR, Johnson KR, Hicks JF, Wing SL, Obradovich JD. High plant diversity in Eocene South America: evidence from Patagonia. Science. 2003;300(5616):122–125. pmid:12677065
- 113. Wilf P, Johnson KR, Cúneo NR, Smith ME, Singer BS, Gandolfo MA, et al. Eocene Plant Diversity at Laguna del Hunco and Río Pichileufú, Patagonia, Argentina. Am Nat. 2005;165(6):634–650. pmid:15937744
- 114. Feruglio E. Descripción geológica de la Patagonia. Yacimientos Petrolíferos Fiscales. Ministerio de Industria y Comercio. Buenos Aires. Tomo II. 1949;1–349.
- 115. Troncoso A. La tafoflora Terciaria de Quinamavida (VII Region, Chile). Bol Museuo Nac Hist Nat Chile. 1992;43:155–178.
- 116. Smith N., Mori S.A., Henderson A., Stevenson D.W. & Heald S.V. Flowering Plants of the Neotropics. The New York Botanical Garden, Princeton University Press, New Jersey, USA; 2004. 594 p.
- 117. Raven PH, Axelrod DI. Angiosperm biogeography and past continental movements. Ann Mo Bot Gard. 1974 Jan 1;61(3):539–673.
- 118. Zuloaga F.O. & Morrone O. (eds.). Catálogo de las plantas vasculares de la República Argentina. II. Angiospermae (Dicotyledoneae). Monographs in Systematic Botany from the Missouri Botanical Garden 1999;64:1–1269.
- 119. Zuloaga FO, Belgrano MJ. The Catalogue of Vascular Plants of the Southern Cone and the Flora of Argentina: their contribution to the World Flora. Rodriguésia. 2015;66(4):989–1024.
- 120. Tortosa RD. El complejo Retanilla-Talguenea-Trevoa (Rhamnaceae). Darwiniana. 1992;223–252.
- 121. León R.J.C., Bran D., Collantes M., Paruelo J.M., and Soriano A. Grandes unidades de vegetación de la Patagonia extraandina. Ecología Austral. 1998;8:125–144.
- 122. Servicio Meteorológico Nacional. Atlas Climatico [Internet]. Servicio Meteorológico Nacional. 658 [cited 2016 Nov 8].
- 123. Iglesias A, Artabe AE, Morel EM. The evolution of Patagonian climate and vegetation from the Mesozoic to the present. Biol J Linn Soc. 2011;103(2):409–422.
- 124. Berry EW. The fossil flora of the Loja Basin in southern Ecuador. John Hopkins Univ Stud Geol. 1929;10:79–135.
- 125. Campbell JD. Angiosperm fruit and leaf fossils from Miocene silcrete, Landslip Hill, northern Southland, New Zealand. J R Soc N Z. 2002;32(1):149–154.
- 126. Kershaw AP. A Late Pleistocene and Holocene Pollen Diagram from Lynch’s Crater, Northeastern Queensland, Australia. New Phytol. 1976;77(2):469–498.
- 127. Stuchlik L. Tertiary pollen spectra from the Ezcurra Inlet Group of Admiralty Bay, King George Island (South Shetland Islands, Antarctica). Stud Geol Pol. 1981;72:109–132.
- 128. Mohr BAR. Eocene and Oligocene sporomorphs and dinoflagellate cysts from Leg 113 drill sites, Weddell Sea, Antarctica. In: Proceedings of the Ocean Drilling Program, scientific results. US Government Printing Office, College Station, Texas; 1990. p. 595–612.
- 129. Blackburn DT, Sluiter IRK. The Oligo–Miocene coal floras of south-eastern Australia. In: Hill RS, editor. History of the Australian vegetation: Cretaceous to recent. Cambridge University Press: Cambridge, UK; 1994. p. 328–367.
- 130. Kooyman RM, Wilf P, Barreda VD, Carpenter RJ, Jordan GJ, Sniderman JMK, et al. Paleo-Antarctic rainforest into the modern Old World tropics: The rich past and threatened future of the “southern wet forest survivors.” Am J Bot. 2014;101(12):2121–2135. pmid:25480709
- 131. Chitaley SD, Kate UR. A petrified rhamnaceous wood from the Deccan Inter-trappean Beds of Mohgaon kalan. Botanique. 1972;3(1):41–44.
- 132. Trivedi BS, Srivastava K. Zizyphoxylon mandlaensis gen. et sp. nov. from the Deccan Intertrappean beds of Mandla District in MP. (India). J Indian Bot Soc. 1982;61:212–215.
- 133. Udhoji SG. Biostratigraphic studies of fresh-water infra- an inter-trappean formations in parts of Madhya Pradesh (IGCP-216: Global bioevents in earth history). Rec Geol Surv India. 1989;122(6):214–215.
- 134. Udhoji SG, Verma K. Palaeontological observations on intertrappean beds in parts of Jabalpur and Mandla districts, Madhya Pradesh. In: Sahni A, Jolly A, editors. Cretaceous event stratigraphy and the correlation of the Indian non-marine strata, Chandigarh. 1990. p. 99–100.
- 135. Guleria JS. A semi-ring porous fossil wood of Ziziphus from the Late Tertiary of Rajasthan. Palaeobotanist. 1992;39:303–308.
- 136. Prakash U. Palaeogene angiospermous woods. Asp Apprais Indian Palaeobot Eds Surange KR Lakhanpal RN Bharadwaj DC Birbal Sahni Inst Palaeobot Lucknow. 1974;306–320.
- 137. Pennington RT, Dick CW. The role of immigrants in the assembly of the South American rainforest tree flora. Philos Trans R Soc Lond B Biol Sci. 2004;359(1450):1611–1622. pmid:15519976
- 138. Carvalho MR, Wilf P, Hermsen EJ, Gandolfo MA, Cúneo NR, Johnson KR. First record of Todea (Osmundaceae) in South America, from the early Eocene paleorainforests of Laguna del Hunco (Patagonia, Argentina). Am J Bot. 2013;100(9):1831–1848. pmid:24018858
- 139. Herrera F, Manchester SR, Hoot SB, Wefferling KM, Carvalho MR, Jaramillo C. Phytogeographic implications of fossil endocarps of Menispermaceae from the Paleocene of Colombia. Am J Bot. 2011;98(12):2004–2017. pmid:22114219
- 140. Hermsen EJ, Gandolfo MA. Fruits of Juglandaceae from the Eocene of South America. Syst Bot. 2016;41(2):316–328.
- 141. Gandolfo MA, Hermsen EJ, Zamaloa MC, Nixon KC, González CC, Wilf P, et al. Oldest known Eucalyptus macrofossils are from South America. PLoS ONE. 2011;6(6):e21084. pmid:21738605
- 142. Cúneo NR, Hermsen EJ, Gandolfo MA. Regnellidium (Salviniales, Marsileaceae) macrofossils and associated spores from the Late Cretaceous of South America. Int J Plant Sci. 2013;174(3):340–349.
- 143. Wilford GE, Brown PJ. Maps of late Mesozoic-Cenozoic Gondwana break-up: some palaeogeographical implications. Hist Aust Veg Cretac Recent. 1994;5–13.
- 144. Cunningham WD, Dalziel IWD, Lee T-Y, Lawver LA. Southernmost South America-Antarctic Peninsula relative plate motions since 84 Ma: Implications for the tectonic evolution of the Scotia Arc region. J Geophys Res Solid Earth. 1995;100(B5):8257–8266.
- 145. Lawver LA, Gahagan LM. Evolution of Cenozoic seaways in the circum-Antarctic region. Palaeogeogr Palaeoclimatol Palaeoecol. 2003;198(1):11–37.
- 146. Pascual R, Ortiz-Jaureguizar E. The Gondwanan and South American Episodes: Two Major and Unrelated Moments in the History of the South American Mammals. J Mamm Evol. 2007 Mar 29;14(2):75–137.
- 147. Wilf P, Cúneo NR, Escapa IH, Pol D, Woodburne MO. Splendid and Seldom Isolated: The Paleobiogeography of Patagonia. Annu Rev Earth Planet Sci. 2013;41(1):561–603.
- 148. Kryshtofovich A. Two ferns and a palm from the Tertiary of the Takashima coal-mines in the Province of Hizen. J Geol Soc Tokyo. 1918;25:25–29.
- 149. Singh H, Prasad M, Kumar K, Rana RS, Singh and S K. Fossil fruits from Early Eocene Vastan Lignite, Gujarat, India: taphonomic and phytogeographic implications. Curr Sci 00113891. 2010 Jun 25;98(12):1625–1632.
- 150. Dorofeev P. Tertiary floras of western Siberia. Moscow-Leningrad: Komarov Botanical Institute, Academia Nauka SSSR; 1963.
- 151. Kvaček Z, Hurník S. Revision of early Miocene plants preserved in baked rocks in the North Bohemian tertiary. Sborník Národního Muzea V Praze Řada B Přír Vědy. 2000;56(1/2):1–48.
- 152. Mai DH, Walther H. Die fundstellen eozäner floren des Weisselster-Beckens und seiner Randgebiete. Mauritianum; 2000.
- 153. Ettingshausen C. Die fossile Flora des Tertiar-beckens von Bilin III. Denkschr K Akad Wiss Math-Naturwiss Kl. 1869;29:1–110.
- 154. Bŭžek Č, Dvořák Z, Kvaček Z, Prokš M. Tertiary vegetation and depositional environments of the Bílina “delta”in the North-Bohemian brown-coal basin. Čas Miner Geol. 1992;37(2):117–134.
- 155. Gregor H-J. Die miozänen Frucht- und Samen-Floren der Oberpfälzer Braunkohle. I. Funde aus den sandigen Zwischenmitteln. Palaeontogr Abt B. 1978;167:8–103.
- 156. Mai D. The middle and upper Miocene floras of the Meuro and Rauno sequences in the Lusatica region. II. Dicotyledones. Palaeontogr Abt B. 2001;257:35–174.
- 157. Kovar-Eder J, Kvacek Z, Zastawniak E, Givulescu R, Hably L, Mihajlovic D, et al. Floristic trends in the vegetation of the Paratethys surrounding areas during Neogene time. In: Bernor R, Fahlbusch Z, Mittmann H-W, editors. The evolution of western Eurasian later Neogene faunas. New York: Columbia University Press; 2004. p. 399–409.
- 158. Jaccard A. Note sur la flore fossile du terrain d’eau douce superior du Locle. Bull Soc Neuchatel Sci Nat. 1858;4:55–56.
- 159. Raniecka-Bobrowska J. Tertiary seed-flora from Konin (central Poland). Inst Geol Biul. 1959;130:159–252.
- 160. Brabenec B. O novém nalezisti tretihorních rostlin ve spodním pásmuvrstevzateckých. Rozpr Cesk Akad Ved Umıní Trída II. 1904;13:1–25.
- 161. WGCPC (Writing Group of Cenozoic Plants of China). Chinese Mesozoic plants. The classification of fossils in China: Chinese plant fossils. Peking: Chinese Institute of Science; 1978. 232 p.
- 162. Ozaki K. Late Miocene and Pliocene floras in central Honshu, Japan. Yokohama: Kanagawa Prefectural Museum; 1991. 188 p. (Bulletin of the Kanagawa Prefectural Museum, Natural Science, Special Issue).
- 163. Berry E. A Miocene Paliurus from the state of Washington. Am J Sci. 1928;5(16):39–44.
- 164. Berry E. A Miocene flora from Grand Coulee, Washington. Geol Surv Prof Pap. 1931;170–C:31–42.
- 165. Smiley CJ. The Ellensburg flora of Washington. Univ Calif Publ Geol Sci. 1963;35:159–275.
- 166. Smiley CJ, Rember B. Composition of the Miocene Clarkia flora. In: Smiley CJ, editor. Late Cenozoic history of the Pacific Northwest. San Francisco: Pacific Division AAAS; 1985. p. 95–112.
- 167. Berry EW. The Lower Eocene Floras of Southeastern North America. U.S. Government Printing Office; 1916. 624 p.
- 168. Manchester SR. Biogeographical relationships of North American tertiary floras. Ann Mo Bot Gard. 1999;472–522.
- 169. Langeron M. Note sur une empreinte remarquable provenant des Cinerites du Cantal Paliurites martyi (Langeron). Bull Trimest Soc Hist Nat Amis Mus Autun. 1902;15:35–96.
- 170. Grote PJ. Studies of a flora from the Pleistocene of Northeastern Thailand. School of Biology, Insitute of Science, Suranaree University of Technology; 2007.
- 171. Traverse A. Pollen analysis of the Brandon lignite of Vermont. Washington D.C.: U.S. Dept. of the Interior, Bureau of Mines; 1955. 107 p. (Report of investigations (United States. Bureau of Mines); vol. 5151).
- 172. Tiffney BH. Re-evaluation of the age of the Brandon Lignite (Vermont, USA) based on plant megafossils. Rev Palaeobot Palynol. 1994 Jul 1;82(3):299–315.
- 173. Averdieck FR. Palynologische Untersuchungen zum Tertiär auf Sylt. Meyniana. 1971;21:1–8.
- 174. Menke B. Pliozäne und ältestquartäre Sporen-und Pollenflora von-Schleswig-Holstein [Internet]. Hannover: E. Schweizerbart’sche Verlagsbuchhandlung; 1976. 200 p. (Geologisches Jahrbuch.; vol. 32).
- 175. Ramírez-Arriaga E, Prámparo MB, Martínez-Hernández E. Angiosperm pollen grains from the Cuayuca Formation (Late Eocene to Early Oligocene), Puebla, Mexico. Palaeontol Electron. 18(1):1–38.
- 176. Akkiraz MS, Kayseri MS, Akgün F. Palaeoecology of coal-bearing Eocene sediments in Central Anatolia (Turkey) based on quantitative palynological data. Turk J Earth Sci. 2008 Mar 14;17(2):317–360.
- 177. Le Houérou HN. Climate, flora and fauna changes in the Sahara over the past 500 million years. J Arid Environ. 1997 Dec 1;37(4):619–647.
- 178. Chesters K.I.M. The Miocene flora of Rusinga Island, Lake Victoria, Kenya. Palaeontographica Abt. B. 1957;101(1–4):30–71.
- 179. Retallack GJ. Middle Miocene fossil plants from Fort Ternan (Kenya) and evolution of African grasslands. Paleobiology. 1992;18(4):383–400.
- 180. Collinson ME, Andrews P, Bamford MK. Taphonomy of the early Miocene flora, Hiwegi Formation, Rusinga Island, Kenya. J Hum Evol. 2009;57:149–162. pmid:19576619