Kynlega stór aldin úr síðtertíerum setlögum á Íslandi / Unusually large samaras from late Miocene sediments in Iceland
... Also, the Miocene floras of Iceland, both macrofloras and microfloras, have been studied in detail and yield no records of Arceuthobium, but Viscum is present (e.g. Grímsson et al. 2005Grímsson et al. , 2007aGrímsson et al. , 2007bDenk et al. 2005Denk et al. , 2010Denk et al. , 2011Grímsson & Símonarson 2008). The earliest American fossil records of Arceuthobium are from the Miocene (summarised by Hawksworth & Wiens 1996). ...
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.
This chapter reviews Cenozoic plant assemblages from the sub-arctic North Atlantic region and their biogeographic implications. Engler's hypothesis about the ‘Arcto-Tertiary element’ remains a fundamental hypothesis about the origin of northern temperate tree genera. The book reviews previous work on the plant fossil record from Paleocene to Pleistocene sedimentary formations of the sub-arctic North Atlantic region. This includes Paleogene plant assemblages from Greenland, the Faroe Islands and Scotland, as well as Neogene floras from Iceland. The Faroe Islands are patchy sub-aerial remnants of a extensive Paleogene lava sequence that is considered part of the Brito-Arctic Igneous Province. In his classic paper from 1985, Tiffney mentions plant genera that are shared between the early Miocene Brandon Lignite Flora of eastern North America and Paleogene and Neogene floras of western Eurasia to illustrate the importance of the North Atlantic Land Bridge. The improved understanding of the history of the NALB is crucial for basic biogeographic assumptions.
Here we describe fossil Bibionidae (Diptera) insects from the late Miocene Hrútagil locality (part of the 9–8 Ma Skarðsströnd–Mókollsdalur formation) in Iceland. This material offers a rare chance to study a fossil insect fauna from a North Atlantic oceanic island. The material includes three species, one from each genera of Bibio, Dilophus and Penthetria, but only the former is sufficiently well preserved to warrant description as a new taxon, Bibio edda sp. nov., most superficially similar to B. brevis Heer, 1849 but differs in wing and tibial characters, among others. Finally, we compare the species to other fossil Bibionidae known from the Miocene of continental Europe.
Well-preserved arthropods are reported from Miocene sedimentary rocks of the Skarðsströnd-Mókollsdalur (9–8 Ma) and Hreðavatn-Stafholt (7–6 Ma) Formations in Iceland. Fossil remains of terrestrial and/or freshwater animals have rarely been reported from the island before. Here we provide the first overview of the surprisingly rich Tortonian fauna from the Hrútagil locality and additional Messinian-aged trichopteran larval cases from the Stafholt locality. The Hrútagil fauna includes representatives of Cladocera (Crustacea: Branchiopoda) and seven insect orders, including several morphotypes of the orders Plecoptera, Dermaptera, Hemiptera (Cercopoidea, Aphididae), Coleoptera, Hymenoptera, Trichoptera (Drusinae), and Diptera (Bibionidae). Previous studies on the Miocene of Iceland have been based principally on pollen analysis and the macrobotanical record with little attention paid to other aspects of the island’s palaeontology. This study provides the first comprehensive systematic description of Miocene arthropods from the northern North Atlantic region and offers the opportunity for a rare glimpse into the late Cenozoic arthropod fauna of Iceland in the context of transatlantic migration and palaeobiogeography and the onset of major global cooling events.
Terrestrial fossils from Late Miocene sediments in the Mókollsdalur area are mainly known for their insect fauna. Plant fossils
and the sedimentological context suggest that most of the macrofossils deposited at Mókollsdalur originate from trees and
shrubs that grew on the slopes around a caldera lake in the highlands. Abundant fossils of aquatic crustaceans, insects, and
plants suggest that the lake and adjacent areas were a diverse ecosystem at the time of deposition. Forests covering the slopes
were dominated by Fagus with a few evergreen elements in the understorey (Ilex, Rhododendron). In contrast, the palynological record points to the presence of mixed oak forests in areas behind the mountain ridge surrounding
the caldera. The poor representation of herbaceous elements in the pollen record may point to a filter effect against pollen
influx from surrounding areas into the lake. Slope exposure may have determined the presence of Fagus or Quercus as is also seen today in cool temperate regions of the northern hemisphere. Overall, the climate appears to be more diversified
than in the older floras with relatively warmer humid conditions windward of the mountains or in sheltered areas close to
the lake and cooler more continental conditions leeward of the mountains.
This chapter provides morphological descriptions including remarks on nomenclatural problems for the macrofossil (M) and palynological (P) record from Iceland. The systematic section starts with Bryophyta (mosses), Lycopodiophyta (clubmosses and spikemosses),
and Pteridophyta (horsetails and true ferns), followed by Gnetophyta, Ginkgophyta, Pinophyta (conifers), and Magnoliophyta
(flowering plants). Families and genera appear in alphabetical order. Incertae sedis are listed at the end of each large taxonomic
group. For each taxon described, stratigraphic and geographic occurrences are provided. Remarks regarding systematic affinities
to coeval and extant taxa are added as well. Most taxa described here are illustrated in the plates accompanying Chaps. 4–11. Macrofossils are stored in the Swedish Museum of Natural History (S), the Icelandic Institute (Museum) of Natural History
(IMNH), and the Geological Museum, Copenhagen (GM). Pollen samples are kept at the Department of Palaeobotany, University
of Vienna. A table summarizing all (morpho)taxa recorded from Iceland with their stratigraphic ranges is provided at the end
of Chap. 12 (Appendix 12.1).
During the past 125 years the history of early angiosperms, interpreted through the fossil leaf record has been largely an
exercise in paleofloristic studies, ignoring evolution. Imprecise identifications of ancient leaves “matched” to extant genera
and families have been used as the basis for reconstructions of paleocommunities and paleoclimates. However, as the result
of careful morphological studies of leaf form, venation and cuticular features new insights into the evolution of angiosperms
are now available. In this paper considerations are given to the usefulness and shortcomings of leaf form, venation and cuticular
analysis as diagnostic tools of plant identification. Many techniques for the study of the morphology of modern and fossil
leaves are included in this paper as well as tables outlining features of leaf venation and the epidermis. Careful morphological
studies of leaf form (such as the venation and epidermal characters emphasized in this paper) will provide better understanding
of the relationships of living angiosperms and transform the fossil leaf record into useful data that can be used to study
the evolution of the angiosperms.
Seed mass is correlated with a number of other plant traits, including dispersal mode, growth form and specific leaf area. Specific leaf area is the main determinant of potential relative growth rate and an indicator of the site quality to which a species is adapted. The relationships with dispersal mode and growth form have consistent form in five datasets from three continents, and each account for about 20-30% of variation in log seed mass. Thus, there is also very substantial variation within growth form and dispersal categories. Much, but not all, of the 20-30% is associated with shifted family composition between growth forms or dispersal modes. Experiments have shown that seedlings of larger-seeded species are better able to survive hazards including deep shade, drought, physical damage and the presence of competing vegetation. If there is a common mechanism under these different hazards, it seemingly must be a `reserve effect', whereby during deployment and early growth larger-seeded species hold a bigger percentage of seed reserves uncommitted to seedling structure and available to support respiration or repair damage. A reserve effect has not yet been demonstrated directly. It remains possible that different mechanisms operate under different hazards. Under a reserve effect, advantages of larger seed size should be temporary, and temporary advantage has indeed been observed with regard to seedling survival under dense shade. Although larger seed mass confers benefits on seedlings, larger seeds must necessarily be produced in smaller numbers per unit of resource allocated. Seed mass is presumed to have evolved as a compromise between these counterposed pressures. Yet there has proved to be surprisingly little difference in average seed mass between very different vegetation regions, at least in temperate climates. Rather, there is startlingly wide variation in seed mass among species growing interspersed with each other. Recent applications of game theory may be capable of accounting for this wide variation between coexisting species, but at present these models are driven by competition among seedling species (as opposed to between seedlings and adults). It remains unclear whether competition among seedlings is a decisive influence on species composition in most of the world's vegetation types.
A new genus and species of fossil angiosperm (Appomattoxia ancistrophora) is established based on well-preserved fruiting units and associated pollen from the Early Cretaceous (Early or Middle Albian) Puddledock locality in the Potomac Group sequence of Virginia, eastern North America. Fruiting units are small, unilocular, and with a single, pendulous, orthotropous seed. The fruit surface is characterized by densely spaced unicellular spines with hooklike tips, which probably functioned in biotic dispersal. Pollen grains adhering to the stigmatic area of many specimens are monocolpate and tectate with granular to columellate infratectal structure, and are similar to dispersed grains assigned to Tucanopollis and Transitoripollis. Comparison of fossil Appomattoxia ancistrophora with extant plants reveals an unusual combination of characters that includes similarities with some magnoliid taxa, particularly Piperales (Piperaceae, Saururaceae) and Laurales (Chloranthaceae), as well as the monotypic ranunculid family Circaeasteraceae. Appomattoxia ancistrophora differs from extant Piperales in having a pendulous rather than erect ovule, and differs from extant Circaeaster in details of the fruit wall, as well as the presence of monosulcate rather than tricolpate pollen.
A new genus and species of fossil angiosperm (Appomattoxia ancistrophora) is established based on well-preserved fruiting units and associated pollen from the Early Cretaceous (Early or Middle Albian) Puddledock locality in the Potomac Group sequence of Virginia, eastern North America. Fruiting units are small, unilocular, and with a single, pendulous, orthotropous seed. The fruit surface is characterized by densely spaced unicellular spines with hooklike tips, which probably functioned in biotic dispersal. Pollen grains adhering to the stigmatic area of many specimens are monocolpate and tectate with granular to columellate infratectal structure, and are similar to dispersed grains assigned to Tucanopollis and Transitoripollis. Comparison of fossil Appomattoxia ancistrophora with extant plants reveals an unusual combination of characters that includes similarities with some magnoliid taxa, particularly Piperales (Piperaceae, Saururaceae) and Laurales (Chloranthaceae), as well as the monotypic ranunculid family Circaeasteraceae. Appomattoxia ancistrophora differs from extant Piperales in having a pendulous rather than erect ovule, and differs from extant Circaeaster in details of the fruit wall, as well as the presence of monosulcate rather than tricolpate pollen.
A new angiosperm genus, Anacostia, with four species (A. marylandensis, A. virginiensis, A. portugallica, A. teixeirae) is described from Early Cretaceous floras in North America and Portugal. Anacostia comprises small, unilocular and one‐seeded fruiting units (each derived from a single carpel) with a sessile and indistinct stigmatic area. There are indications that a fleshy layer was originally present in the fruit wall. The seeds are anatropous, testai, and apparently derived from a bitegmic ovule. Pollen grains adhering to the stigmatic area and fruit wall are monoaperturate and trichotomocolpate or monocolpate. The pollen tectum is distinctly graded, reticulate to foveolate with the size of lumina decreasing towards the aperture and towards the proximal pole. The four species show substantial similarities in morphology, and in the anatomy of fruit, seed, and pollen, but can be distinguished by size and shape, as well as details of the fruit and seed wall. The Anacostia fruiting units are similar in several respects to those of the chloranthoid fossil Couperites described from mid‐Cretaceous sediments in eastern North America, but differ in details of fruit wall, seed wall, and associated pollen. The combination of separate fruiting units (carpels) containing a single anatropous, testai seed and trichotomocolpate/monocolpate pollen indicates a relationship between Anacostia and certain extant magnoliids and monocotyledons.
The major diversification of flowering plants (angiosperms) in the Early
Cretaceous, between about 130 and 90 million years ago, initiated
fundamental changes in terrestrial ecosystems and set in motion
processes that generated most of the extant plant diversity. New
palaeobotanical discoveries, combined with recent phylogenetic analyses
of morphological and molecular data, have clarified the initial phases
of this radiation and changed our perspective on early angiosperm
evolution, though important issues remain unresolved.
The known fossil fruits and leaves of Acer from western North America represent 91 species and 28 sections, 12 of which are extinct and are described as new sections of Acer. Sixty-four species are described as new, 2 new combinations are proposed, and 6 species are left unnamed; 21 have been previously described. The most diverse sections of Acer in the Tertiary of western North America are the extinct Glabroidea (at least 13 species), Negundo (9 species), Macrophylla (8 species), and Eriocarpa (8 species), Descriptions of almost all the species are presented, and all species are illustrated. Although Aceraceae are considered to be derivatives of an early, extinct group of Sapindaceae, Paullinieae (rather than Harpullieae) are considered 10 be the extant tribe of Sapindaceae most closely related 10 Aceraceae. A cladistic analysis of Aceraceae and of Acer includes Sapindaceae, Dipteronia, and the "Acer" arcticum complex, which is thought to represent an extinct genus of Aceraceae. The cladistic analysis based on extant Acer results in the subdivision of Acer into 4 informal groups: Spicata Group, Macrantha Group, Macrophylla Group (including section Acer and allies), and the Platanoidea Group. Timing of first appearances of the various groups and sections in the fossil record generally parallel the cladistic analysis. The Spicata Group is the oldest (latest Paleocene); this group includes three extinct sections in the early middle Eocene, all of which became extinct by the late middle Eocene. First known in the early middle Eocene are extinct sections of the Macrantha and Macrophylla groups; extant sections of these groups appear by the late middle to early late Eocene. The Platanoidea Group appeared in the late middle Eocene, and extant sections appeared by the latest Eocene. A fifth group, the Orba Group, is known only as fossil and represents sections that diverged between the divergences of the Macrantha and Macrophylla groups. Diversification of Acer at the sectional level appears to have taken place in a volcanic upland region in western North America during the Eocene. Although possibly a mesothermal genus during the late Paleocene and early Eocene, Acer diversified greatly during the middle and late Eocene as microthermal climates increased in area. During the early middle Eocene, 10 sections (all extinct) and 11 species of Acer are known. During the late middle to late Eocene, Acer reached maximal diversity in western North America: at least 34 species and 15 sections are known, and occurrences of other species and sections can be inferred. Acer, however, was apparently a very minor element in Eocene microthermal vegetation. Sectional diversification of Acer was largely completed by the end of the Eocene, although a few derivative sections may be of post-Eocene age. Acer reached maximum abundance in western North America during the early and middle Miocene: at least 29 species and 10 sections are known. Following the middle Miocene, Acer underwent a major decline in diversity and abundance in western North America; this decline was due primarily to declining summer temperatures at high latitudes and increasing aridity at middle latitudes. Present distributions of sections and species of Acer have resulted from a complex history of dispersals and vicariant events, most of which are related to climate. Probable origin of many extant Asian sections of Acer in western North America during the Eocene implies many dispersals from North America to Asia during the Eocene. Many extinct and extant sections of Acer became extinct on North America during the late Eocene and early Oligocene; some of these extant sections re-entered North America during the late Oligocene and Miocene but again became extinct during the Miocene. Cladistic relationships of series Saccharodendron strongly indicate an origin in western Eurasia. Appearance of this section in North America during the early Miocene and absence of a Beringian fossil record indicate long-distance dispersal across the Atlantic Ocean. Absence of a Tertiary record in western North America of Palmata indicates a long-distance dispersal from eastern Asia.
Seeds and fruits of Early Cretaceous (Barremian-Aptian) angiosperms from the Famalicão locality in Portugal were analyzed to establish seed and fruit size (volume) distributions and to infer the proportion of animal-dispersed fruits. On the basis of a sample of 106 angiosperm fruit and seed taxa, the average seed size was 0.78 mm3 (range 0.02-6.86 mm3), whereas the average fruit size was 2.06 mm3 (range 0.12-8.34 mm3). Variation in seed size among taxa is smaller than in modern plant communities, but within-taxon variation is similar to that known for extant plants. No significant difference in the size of "fleshy" versus other fruits was observed. The proportion of fleshy fruits was 24.5%. This high figure was surprising and indicates that the significance of animal dispersal during an early stage in angiosperm evolution has been underestimated. We suggest that reptiles and multituberculates, and perhaps other mammals and birds as well, were the likely seed dispersers and that the early angiosperms from Famalicão probably were herbs or small shrubs that inhabited a semiopen coniferous woodland.