Miocene Vegetation Research Articles

Woods from the Miocene Bakate Formation, Ethiopia: Anatomical characteristics, estimates of original specific gravity and ecological inferences

An assemblage of permineralized woods from the Miocene Bakate Formation, Fejej Plain, Ethiopia, is described. This assemblage of twelve wood types differs from other Miocene wood assemblages known from Ethiopia. Cell wall percentages of the woods were determined to estimate the original specific gravities of the woods in order to better understand the Miocene vegetation and environment of Fejej. The relatively high specific gravities (0.63 to 0.82) and numerous and narrow vessels of these Miocene woods are characteristics of dry deciduous forests or woodlands. The affinities of some of the Fejej woods could not be determined because critical diagnostic features could not be determined, but others have characteristics seen in the Sapotaceae, Leguminosae, Combretaceae, and Bignoniaceae (a ring porous wood). None of the families represented by a fruit and seed assemblage from Fejej are represented in the wood assemblage.

Late Miocene vegetation reconstruction with the CARAIB model

Climatic outputs from the atmospheric general circulation model ECHAM4 coupled to a mixed layer ocean model are used as inputs to the CARAIB global vegetation model to reconstruct the distribution of vegetation and the biosphere carbon stocks over the continents during the Late Miocene (Tortonian). The results show significant changes in the geographical distribution of vegetation during the Late Miocene compared to the present with a reduction of desert areas and an expansion of tropical seasonal forests, which reached temperate latitudes. These changes in vegetation distribution are accompanied by a moderate increase of the total biosphere carbon stock by 159 Gt. Sensitivity tests to atmospheric CO 2 have also been performed with the vegetation model only, i.e., while keeping constant all climatic variables to their reference Tortonian state. These tests point out the potential importance of CO 2 fertilization both regarding vegetation distribution and biosphere carbon storage. The impact of an atmospheric CO 2 decrease (from 280 to 200 ppmv) or increase (from 280 to 560 ppmv) on the vegetation distribution appears to be at least as large as that of the climate change between the Tortonian and the present, while in terms of carbon storage the impact of atmospheric CO 2 is far much larger than the climatic one. Although the actual response of vegetation to CO 2 fertilization may be much smaller than its theoretical response in the model, these results emphasize the need to consider atmospheric CO 2 as an important parameter for palaeovegetation reconstructions.

Evolution of hypsodonty in equids: testing a hypothesis of adaptation

The independent acquisition of high-crowned cheek teeth (hypsodonty) in several un- gulate lineages (e.g., camels, equids, rhinoceroses) in the early to middle Miocene of North America has classically been used as an indication that savanna vegetation spread during this time. Implicit in this interpretation is the untested assumption that hypsodonty was an evolutionary response to feeding in open habitats, either due to a change in food source (from browse to graze) or to in- creased incorporation of airborne grit in the diet. I examined the adaptive explanation for hypso- donty in equids using criteria pertaining to process and pattern of adaptations set up in the com- parative-methods literature. Specifically, I tested whether hypsodonty appeared coincident with or just after the spread of open, grass-dominated habitats in the Great Plains of North America. Phytolith (plant opal) analysis of 99 phytolith assemblages extracted from sediment samples from Montana/Idaho, Nebraska/Wyoming, and Colorado were used to establish the first contin- uous record of middle Eocene-late Miocene vegetation change in the northern to Central Great Plains. This record was compared with the fossil record of equids from the same area in a phy- logenetic framework. The study showed that habitats dominated by C 3 grasses were established in the Central Great Plains by early late Arikareean ($21.9 Ma), at least 4 Myr prior to the emergence of hypsodont equids (Equinae). Nevertheless, the adaptive hypothesis for hypsodonty in equids could not be rejected, because the earliest savanna-woodlands roughly co-occurred with members of the grade constituting the closest outgroups to Equinae (''Parahippus'') showing mesodont dentition. Expla- nations for the slow evolution of full hypsodonty may include weak and changing selection pres- sures and/or phylogenetic inertia. These results suggest that care should be taken when using func- tional morphology alone to reconstruct habitat change.

Late Miocene vegetation and palaeoenvironments of the Drygalski Formation, Heard Island, Indian Ocean: evidence from palynology

Well sorted, fine lithic sandstone within the Drygalski Formation at Cape Lockyer on the southern tip of Heard Island, preserves a diverse terrestrial palynoflora as well as marine diatoms and a few foraminifera. A combination of these elements suggests a Late Miocene age (10–5 Ma). The palaeovegetation was markedly different from that presently on the island, and appears to comprise at least two ecologically distinct communities: open heath or herbfield dominated by grasses and Asteraceae, and a more mesophytic community dominated by ferns but also including lycopods and angiosperms such as Gunnera. This may have represented a coastal flora similar to the ‘fern-bush’ community that exists now on Southern Ocean islands north of the Antarctic Polar Frontal Zone, and in Tierra del Fuego; however, there is no evidence of tree species in the local flora and trace amounts of tree pollen present may have blown in from other landmasses in the region.

Angiosperm fruit and leaf fossils from Miocene silcrete, Landslip Hill, northern Southland, New Zealand

Impressions of fruits and leaves of angiosperms recovered from Landslip Hill near Gore, eastern Southland, include some showing features attributable to Corynocarpus, others that may belong to Avicennia, Pomaderris, and Pouteria as well as the already described Fagaceae and Casuarinaceae. These, along with araucariacean fossils, allow the reconstruction of a warm temperate Early Miocene vegetation in eastern Southland, which may have been coastal.

Comparing Early to Middle Miocene floras and probable vegetation types of Oberdorf N Voitsberg (Austria), Bohemia (Czech Republic), and Wackersdorf (Germany)

The Early Miocene vegetation of western Styria, Austria, is reconstructed on the basis of detailed investigations of leaves and diaspores from the mining area Oberdorf N Voitsberg. In this paper, the flora and probable vegetation are compared with other assemblages of similar age from the Czech Republic and Germany to elucidate the diversity of wetland and mesophytic plant communities. The floristic composition and the vegetational units represented in Oberdorf are compared to the middle part of the Most Formation (M Most Fm), Cypris Shale, Mydlovary Formation (Mydlovary Fm) of Bohemia, and the Wackersdorf mining area of Bavaria. Among these sites, Oberdorf is extremely poor in hydrophytes and reed-like monocotyledons, indicating rare pond-like habitats as well as possibly more closed swamp forest conditions than, e.g. in the M Most Fm. In Oberdorf, relatively high pH-values in the lignite-forming swamps and the possible scarcity of acidic, nutrient-poor (sandy) soils have probably influenced the floristic composition of the azonal communities. The peat-forming associations in all regions share the abundance of Glyptostrobus europaeus. However, distinct differences in the accompanying elements, such as Taxodium dubium (present and abundant only in the M Most Fm) indicate even stronger floristic variability of Early(/Middle) Miocene peat-forming and riparian plant communities than previously expected. The virtual absence of Pinus, Engelhardia, Comptonia, and probably also of Quercus kubinyii/ Quercus drymeja in the megafossil record of Oberdorf can possibly be explained by the edaphic conditions. The abundance of Sequoia abietina (absent in all the other compared sites), which we assign to riparian (and mesophytic) forests in Oberdorf, may have been favoured by rich alluvial soils. In the mesophytic associations, thermophilous elements of the Lauraceae, Mastixiaceae, Symplocaceae, and Rutaceae are diverse. Usually they include Trigonobalanopsis rhamnoides/ Trigonobalanopsis exacantha, an evergreen Fagaceae. This assemblage type corresponds with the Younger Mastixioid Flora sensu Mai. The Younger Mastixioid Flora is best developed in Wackersdorf, less distinct in Oberdorf, and likely in the Cypris Shale and Mydlovary Fm. It is not traceable in the M Most Fm.

Miocene ungulates and terrestrial primary productivity: where have all the browsers gone?

Progressive changes are observed in both the composition of mammal faunas and vegetation during the Miocene epoch [24-5 mega-annum (Ma)]. These changes are usually interpreted as a response to climatic changes. In the traditional view, forests or woodlands gradually gave way to more open habitats, with grazing (grass-eating) ungulate (hoofed) mammal species replacing the browsing (leafy-vegetation-eating) species as grasslands expanded. However, data from fossil assemblages in the Great Plains region of North America show that this faunal change was not a one-for-one replacement of browsers by grazers, as usually thought. Typical late early Miocene (17 Ma) fossil communities included extraordinarily high numbers of browsing ungulate species, comprising a fauna that cannot be directly analogized with any present-day community. Both maximum species richness of all ungulates and the proportion of browsers declined steadily in ungulate communities through the middle Miocene, to levels comparable to those of the present by the late Miocene. The resulting dramatic, cumulative loss of browsing species constitutes one of the strongest faunal signals of the late Tertiary (but was not a single "event"). We suggest that the early Miocene browser-rich communities may reflect higher levels of primary productivity in Miocene vegetation, compared with equivalent present-day vegetation types. The observed decline in species richness may represent a gradual decline in primary productivity, which would be consistent with one current hypothesis of a mid-Miocene decrease in atmospheric CO2 concentrations from higher mid-Cenozoic values.

Reconstruction of a Czech Early Miocene vegetation

Methods used by some archaeological botanists to analyse their data can be successfully applied to certain aspects of geobotany. Presence/absence geobotanical records can be studied by multivariate statistical methods to yield lists of ecologicallyassociated taxa. A simple, parametrical, quantitative description of the samples at the more abstract level of plant associations can then be made, using the representation in the original samples of the elements of these lists. When applied to the macrobotanical evidence from the North Bohemian Basin, the relationships between the associations confirmed the patterns that had been suspected previously. As large-scale climatic changes did not seem to influence the fossil record, it was possible to treat the samples as though they were contemporary. The spatial distributions of the associations could therefore be represented as contoured maps. These maps identify which associations were autochthonous, which ones were allochthonous, and whence the allochthonous fossils came and how far they may have travelled.

Paleoecology of a Miocene flora from the Shanwang formation, Shandong province, northern East China

Abstract The Shanwang Formation, which is late Early to early Middle Miocene based on radiometric dates and vertebrate fossils, was deposited in a small intermontane lake basin (N. Lat. 36.5°) and contains a rich assemblage of plant and animal fossils. The chief plant families represented by pollen taxa are Fagaceae, Juglandaceae, Betulaceae, Ulmaceae, Hamamelidaceae and Pinaceae. The combined pollen and leaf data indicate that the Miocene vegetation of the Shanwang area was mixed deciduous and evergreen broad‐leaved forest with a humid warm‐temperate to subtropical climate. In contrast, the modern vegetation is a deciduous broadleaved forest, that contains very few subtropical elements. The average annual temperature at Shanwang was similar to that of today. The main difference between the modern and Miocene climates is that the annual temperature range has increased (colder winters), and precipitation which was evenly distributed is now highly seasonal (winter dry). A comparison between the fossil polle...

Late eocene to early Miocene vegetation and climate history of New Zealand

Abstract There were some major shifts in species dominance in the vegetation of the Late Eocene to Early Miocene in New Zealand. In the Middle Eocene (Bortonian) the vegetation was dominated by Casuarina and several species of Proteaceae. This association was replaced in the Late Eocene (Kaiatan) by one dominated by the Nothofagus fusca group, in which Casuarina was of minor importance. In the latest Eocene (late Kaiatan and Runangan), the Nothofagus fusca group was replaced by the Nothofagus brassii group, which remained dominant until the Early Miocene. The dominance of Nothofagus in the Late Eocene to Early Miocene indicates that the climate was predominantly cool-temperate. At the maximum cooling in the Early Oligocene, the Nothofagus brassii group was abundant. The vegetational data do not support the interpretation, based on oxygen isotope studies, that the climate was warm-temperate throughout much of the Late Eocene. Although there is no complete modern analogue of the Late Eocene to Early Miocene...

Intimations on the Tertiary vegetation of southern Africa

Fossil pollen sequences from the Cape Peninsula and the Saldanha region indicate that sub tropical vegetation and climates existed in these regions during the Miocene. The pollen record from the Cape Peninsula may point to the extinction of some taxa by the terminal Miocene/Early Pliocene with the subsequent strong development of macchia. This major change can probably be related to the maximum build-up of the Antarctic ice-cap in the latest Miocene and the accompanying profound palaeoceanographic changes such as the major cooling of the Benguela current with its effect on the aridification of the Namib desert, and the global glacio-eustatic sea level drop.Parallel palynological and lithological studies in the Saldanha region show that prominent Miocene vegetation shifts were linked to profound local changes in the palaeoenvironment associated with the northward migration of the Miocene Berg River. Such studies are of paramount importance for the possible assessment of the causes of changes in the palaeoenvironment and should first be carried out at many more sites over a wide region. It is to some extent premature to draw firm conclusions as to the origin and migration of some taxa in southern Africa. The record of very primitive angiosperms such as the ClavatipolleniteslAscarina complex and Winteraceae is of considerable phytogeographic interest.

LATE CENOZOIC EVOLUTION OF TROPICAL LOWLAND VEGETATION IN VERACRUZ, MEXICO.

Veracruz is physiographically the most diverse state in Mexico, with altitudes ranging from sea level to the highest peak in Mexico (Pico de Orizaba, 5747 m). This diversity in environments is reflected in a complex mosaic of vegetation estimated at 8000-10,000 species. Studies by GomezPompa (1973) have identified the principal plant communities of Veracruz and provide information on their ecology, composition and distribution. Recently paleobotanical data has become available that, with better understanding of present-day vegetation, reveal some trends in the Cenozoic evolution of lowland communities in Veracruz. An assemblage of 110 identified fossil pollen and spores has been recovered from lignites of the Paraje Solo formation near Coatzacoalcos, Veracruz, Mexico (Table 1). The age of the sediments is upper Miocene and the microfossils thus represent remnants of a vegetation occupying lowlands and adjacent slopes of the Sierra Madre Oriental approximately 10-12 million years ago. With the data available on modern vegetation, these fossils may be arranged into paleocommunities and a comparison made between fossil and modern biotas. Some similarities are evident, together with distinct differences, especially with regard to the Tropical Rain Forest, arid lowland vegetation, and communities suspected (but not proven) to result from anthropogenic influences. A summary of upper Miocene and modern vegetation from southeastern Veracruz is presented in Figure 1. The present-day communities are listed along the left and bottom of the chart with three east-west transects shown along the eastern escarpment from about 1700 m elevation to the Gulf Coast (Gomez-Pompa, 1973). Fossil taxa are placed according to known natural occurrences and may appear in more than one paleocommunity. In a few cases pollen of two genera could not consistently be distinguished in the fossil condition (Eugenia/Myrcia, Combretum/Terminalia, Hampea/Hibiscus). An occasional wellpreserved, critically oriented grain has indicated the probable presence of each genus, and all are included in reconstruction of the paleocommunities although estimates of the relative abundance of these taxa are not possible. The Palmae and Gramineae are listed only for palm stands and savannas but pollen of palms and grasses (and Compositae) are found in all samples, and the modern plants occur scattered throughout most types of vegetation in Veracruz. Pollen of the Lauraceae does not fossilize or survive processing techniques. The criteria used to estimate presence or absence and relative importance of various paleocommunities in the Miocene vegetation are a) occurrence of pollen of the dominants, b) presence of genera characteristically associated with a particular vegetation type, as opposed to wide-ranging genera occurring in several types of communities, and c) abundance of each pollen type, with compensation for distance from the depositional basin, differential pollen production, and nature of the pollination mechanisms (to the extent these data are available).

The Secondary Rocks of Scotland

General Introduction The Highlands of Scotland have long been recognized as an unrivalled field of study for the physical geologist; but to the stratigraphical geologist and the palæontologist, who seek for evidence to aid them in reconstructing the geographical features and determining the biological characteristics of successive geological periods, they have, till of late years, been regarded as comparatively barren of interest. An exception to this general statement must be made, however, in favour of the Old Red Sandstone of the district, which has yielded such admirable results to the studies of Murchison, Sedgwick, Malcolmson, Hugh Miller, Agassiz, and others. Charles Peach's discovery in 1854 of Silurian fossils in Sutherland has already borne the most important fruit, and, in the hands of Murchison, Ramsay, Geikie, Harkness, and Jamieson, has afforded the necessary clue for determining the age of the great Primary masses of the Highlands. Similarly the discovery by the Duke of Argyll of Miocene vegetation in beds intercalated with the basalts of Mull has been the starting-point in elucidating the history of the Tertiary period in the Highlands. Professor Geikie has already laid before this Society the first of a series of papers in which he proposes to treat this interesting subject. The Secondary strata of the same area were, at so early a period as 1826, made the object of an admirable general survey by the late Sir Roderick Murchison; but the progress of geological science since that date appears to create a demand, and at the same