Premise
The Fagaceae comprise around 1000 tree species in the Northern Hemisphere. Despite an extensive fossil pollen record, reconstructing biogeographic patterns is hampered because it is difficult ...to achieve good taxonomic resolution with light microscopy alone. We investigate dispersed pollen of Fagaceae from the Miocene Søby flora, Denmark. We explore the latitudinal gradient in Fagaceae distribution during the Miocene Climatic Optimum (MCO) in Europe and the Northern Hemisphere to compare it with the Eocene Warmhouse and the present.
Methods
We investigated dispersed pollen using light and scanning electron microscopy. We assessed biogeographic patterns in Fagaceae during two warm periods in Earth history (MCO, Eocene) and the present.
Results
Eight species of Fagaceae were recognized in the Søby flora. Of these, Fagus had a continuous Mediterranean to subarctic distribution during MCO; Quercus sect. Cerris and castaneoids had northern limits in Denmark, and evergreen Quercus sect. Ilex in Central Europe. In a northern hemispheric context, Fagus and sections of Quercus had more northerly distribution limits during Eocene and MCO with maximum northward extensions during Eocene (Fagus, castaneoids) or Oligo‐Miocene (Quercus sects. Cerris and Ilex). The known distribution of the extinct Tricolporopollenites theacoides during MCO included Central Europe and East China, while this taxon thrived in South China during Eocene.
Conclusions
More northerly distributions during MCO and Eocene probably were determined by temperature. In contrast, fossil occurrences in areas that are arid or semi‐humid today were determined by maritime conditions in these areas (western North America, Central Asia) during the Cenozoic.
As the third part of an ongoing investigation of middle Miocene palynofloras in the Yatağan Basin (YB), southwestern Anatolia, the palynofloras of the Salihpaşalar lignite mine in the main YB were ...studied. Seven types of algal spores, aplanospores/zygospores or cysts, six types of lycophyte and fern spores, 12 types of gymnosperm pollen and 90 types of angiosperm pollen were identified. Of a total of ca. 140 plant taxa described from the YB, over 10% are confined to the Salihpaşalar assemblage. Differences between coeval palynofloras of the Sekköy Member might reflect changing or prograding depositional environments. A number of rare accessorial taxa reflect these local differences:
Pilularia
,
Valeriana
,
Drosera
and
Persicaria
aff.
amphibia
only occur at Salihpaşalar and are typical of shallow water or temporary ponds associated with a lake shore. Apart from this, all the palynofloras, originating from the lignite seams and overlying limnic limestones (uppermost Turgut and Sekköy Member), of the YB are strongly indicative of extensive woody vegetation with a dominance of diverse Fagaceae and Pinaceae. In addition, a list comparing the well-documented YB palynomorphs to morphologically similar palynomorphs of published late early to middle Miocene plant assemblages of western Anatolian was compiled. Such a comparison reveals that in many instances different taxon names have been used to denote the same taxa. Hence, resolving these synonymies is a prerequisite of any meaningful comparison of palynofloras in the region.
Diospyros is a large genus of woody flowering plants with a predominantly subtropical and tropical modern distribution. Fossils attributed to Diospyros are mainly leaf impressions from Cretaceous and ...Cenozoic strata across the Northern Hemisphere. However, it is difficult to assign such fossils to Diospyros because genus-diagnostic leaf characteristics remain to be identified. Unequivocal fossil records of Diospyros are few, including staminate flowers with in situ pollen from the late Eocene of South Australia and dispersed pollen from Cenozoic strata in the Northern Hemisphere. Here, we investigated dispersed pollen and calyx remains from Miocene deposits of Denmark using a combined scanning electron/light microscopy approach. Tricolporate, relatively large pollen with lalongate pori and long bow-shaped colpi and a distinctive micro/nanorugulate exine ornamentation together with persistent 4-lobed flower calyces allow unambiguous identification of the genus. Based on the large size of the calyx, we describe a new fossil-species of Diospyros. Further, a review of the fossil pollen record of Diospyros shows that, in addition to the Australian record, the genus was present in South China, western North America and Europe during the Eocene and in East and South Africa and Central Asia during the Oligo-Miocene. Although still scanty, the pollen record can contribute vital information for time-calibrated molecular phylogenies to resolve conflicting biogeographic inferences. A thorough description of the historical biogeography of Diospyros is still in its infancy. While we initiate such a study here, development of a comprehensive picture will require further studies of dispersed pollen grains with high taxonomic resolution.
The former family Taxodiaceae is currently treated as nine genera in five subfamilies of the family Cupressaceae. Pollen of the 'taxodiaceous' Cupressaceae typically has a papilla in the leptoma area ...and is common in Cenozoic strata because some of its genera were key elements in lignite forming swamp forests. Dispersed fossil pollen of this group are often assigned to particular genera and, based on the modern ecologies of these taxa, to particular palaeoenvironments. In this study, we investigated pollen of all nine genera of the former Taxodiaceae using light and scanning electron microscopy to evaluate whether pollen morphology can be used to discriminate modern genera of this paraphyletic group. We found few genus- or subfamily-diagnostic characters among members of taxodiaceous Cupressaceae. Features such as orbiculae and pollen and leptoma size cannot be used to discriminate subfamilies. However, three basal subfamilies share short papillae, whereas in two more derived clades (Sequoioideae and Taxodioideae) papillae are markedly longer. In the generally non-papillate core Cupressaceae, the leptoma (aperture) area may or may not possess a distinct circular thinning as also found in the basal grade of taxodiaceous Cupressaceae. Our results show that it is difficult if not impossible to distinguish genera of the ecologically distinct Taxodioideae and Sequoioideae based on pollen morphology. In view of a much wider ecological amplitude of many taxodiaceous Cupressaceae during large parts of the Cenozoic, we conclude that it is not recommendable to infer particular palaeoenvironments on the basis of dispersed taxodiaceous pollen grains alone.
Middle Eocene interbasaltic deposits of Hareø, West Greenland, have yielded a rich leaf and fruit record, which was described in the second half of the nineteenth century. In this study, we describe ...dispersed spores and pollen from the Aumarûtigssâ Member of the Hareøen Formation in order to obtain a more comprehensive picture of the late middle Eocene vegetation of West Greenland. The spore/pollen assemblage, derived from a resinite-rich coal bed, comprises 123 taxa, of which 14 belong to mosses, ferns and fern-allies, 14 to gymnosperms, and 95 to angiosperms. The most diverse groups of angiosperms are Fagales, comprising 27 taxa, and Rosales, represented by nine taxa. Along with conifers belonging to Pinaceae, these groups reflect the temperate character of the Hareø flora. In addition, a few 'exotic' elements include cycads probably belonging to an extinct temperate lineage that was widespread across the Northern Hemisphere during the Paleogene, palm trees, members of Mastixioideae and Santalaceae, both of which were characteristic elements of more southern warm temperate floras of Europe. A detailed comparison with macrofossil and spore/pollen assemblages of roughly coeval sites from Axel Heiberg Island (Canada), Spitsbergen (Arctic Ocean), and ODP site 151-913B in the Norwegian-Greenland Sea, show a highly consistent picture of the vegetation during this time.
Summary
Previous paleobotanical work concluded that Paleogene elements of the sclerophyllous subhumid vegetation of western Eurasia and western North America were endemic to these disjunct regions, ...suggesting that the southern areas of the Holarctic flora were isolated at that time. Consequently, molecular studies invoked either parallel adaptation to dry climates from related ancestors, or long‐distance dispersal in explaining disjunctions between the two regions, dismissing the contemporaneous migration of dry‐adapted lineages via land bridges as unlikely.
We report Vauquelinia (Rosaceae), currently endemic to western North America, in Cenozoic strata of western Eurasia. Revision of North American fossils previously assigned to Vauquelinia confirmed a single fossil‐species of Vauquelinia and one of its close relative Kageneckia.
We established taxonomic relationships of fossil‐taxa using diagnostic character combinations shared with modern species and constructed a time‐calibrated phylogeny.
The fossil record suggests that Vauquelinia, currently endemic to arid and subdesert environments, originated under seasonally arid climates in the Eocene of western North America and subsequently crossed the Paleogene North Atlantic land bridge (NALB) to Europe. This pattern is replicated by other sclerophyllous, dry‐adapted and warmth‐loving plants, suggesting that several of these taxa potentially crossed the North Atlantic via the NALB during Eocene times.
See also the Commentary on this article by Hill & Kahn, 238: 2261–2263.
Abstract
Background and Aims
Cork oaks (Quercus section Cerris) comprise 15 extant species in Eurasia. Despite being a small clade, they display a range of leaf morphologies comparable to the largest ...sections (>100 spp.) in Quercus. Their fossil record extends back to the Eocene. Here, we explore how cork oaks achieved their modern ranges and how legacy effects might explain niche evolution in modern species of section Cerris and its sister section Ilex, the holly oaks.
Methods
We inferred a dated phylogeny for cork and holly oaks using a reduced-representation next-generation sequencing method, restriction site-associated DNA sequencing (RAD-seq), and used D-statistics to investigate gene flow hypotheses. We estimated divergence times using a fossilized birth–death model calibrated with 47 fossils. We used Köppen profiles, selected bioclimatic parameters and forest biomes occupied by modern species to infer ancestral climatic and biotic niches.
Key Results
East Asian and Western Eurasian cork oaks diverged initially in the Eocene. Subsequently, four Western Eurasian lineages (subsections) differentiated during the Oligocene and Miocene. Evolution of leaf size, form and texture was correlated, in part, with multiple transitions from ancestral humid temperate climates to mediterranean, arid and continental climates. Distantly related but ecologically similar species converged on similar leaf traits in the process.
Conclusions
Originating in temperate (frost-free) biomes, Eocene to Oligocene ranges of the primarily deciduous cork oaks were restricted to higher latitudes (Siberia to north of Paratethys). Members of the evergreen holly oaks (section Ilex) also originated in temperate biomes but migrated southwards and south-westwards into then-(sub)tropical southern China and south-eastern Tibet during the Eocene, then westwards along existing pre-Himalayan mountain ranges. Divergent biogeographical histories and deep-time phylogenetic legacies (in cold and drought tolerance, nutrient storage and fire resistance) thus account for the modern species mosaic of Western Eurasian oak communities, which are composed of oaks belonging to four sections.
The continued investigation of the middle Miocene palynoflora from the Lavanttal Basin reveals numerous additional angiosperm taxa. The Myrtales to Ericales pollen record documented here comprises 46 ...different taxa belonging to Onagraceae (Ludwigia), Ericaceae (Craigia, Reevesia, Tilia), Anacardiaceae (Pistacia), Rutaceae (Zanthoxylum), Sapindaceae (Acer), Santalaceae (Arceuthobium), Amaranthaceae, Caryophyllaceae, Polygonaceae (Persicaria, Rumex), Cornaceae (Alangium, Cornus, Nyssa), Ebenaceae (Diospyros), Ericaceae (Andromeda, Arbutus, Empetrum, Erica), Sapotaceae (Pouteria, Sideroxylon), Styracaceae (Rehderodendron) and Symplocaceae (Symplocos). Köppen signatures of potential modern analogues of the additional fossil woody elements confirm the hypothesis of a subtropical (Cfa, Cwa) climate at lower elevations and subsequent transition into a temperate climate with altitudinal succession (Cfa → Cfb/Dfa → Dfb; Cwa → Cwb → Dwb-climate). The fossil plants represent different vegetation units, from wetland lowlands to well-drained montane forests. Many of the fossil taxa have potential modern analogues that can be classified as nemoral and/or meridio-nemoral and/or semihumid-meridional vegetation elements. New is the recognition of oreotropical elements, which are direct indicators for a substantial altitudinal gradient.
Fig. 10 LM overview (a, d, g, j, m), SEM overview (b, e, h, k, n) and SEM detail (c, f, i, l, o, p) micrographs of Amaranthaceae, Droseraceae, Polygonaceae, Sapotaceae and Oleaceae pollen.
a–c
...Drosera
sp. (S153636). d–f
Persicaria
sp./
Persicarioipollenites pliocenicus
(S153634). g–i Amaranthaceae gen. Indet. 3 (S153636)
We investigated a palynological section from middle Miocene sediments at Eskihisar (south‐western Anatolia) to establish biogeographic links of the palynoflora and to infer the palaeoenvironment. ...Four algal palynomorphs, nine spore taxa, eight gymnosperms, three monocots and 67 dicot pollen types were encountered and investigated using the ‘single grain method’ that combines light microscopy and scanning electron microscopy. Two pollen zones reflect different phases of basin development. Zonal vegetation remained fairly stable across the section and reflects heterogeneous environments including broad‐leaved deciduous forest, subtropical forest and sclerophyllous and semi‐evergreen oak forest. Conifers were accessory elements in the broad‐leaved deciduous forest communities and replaced these at higher elevations. Some herbaceous taxa (Plumbaginaceae) indicate scattered occurrences of sandy and/or rocky soils. Biogeographic affinities are general Northern Hemisphere, North American and East Asian, as also suggested by the macrofossil record. Only two taxa provide potential biogeographic links with the African flora. This suggests that biome shifts of plant taxa between African subtropical/tropical biomes and Anatolian (western Eurasian) temperate forests and shrublands may have been rare in the middle Miocene.
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