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Late Miocene (late + miocene)
Selected AbstractsGeochronological evidence for pervasive Miocene weathering, Minas Gerais, BrazilEARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2004Isabela de O. Carmo Abstract 40Ar/39Ar laser incremental-heating analyses of 22 individual grains of supergene cryptomelane from three weathering pro,les, up to 400 km apart, in the Rio Doce valley and Barbacena regions at Minas Gerais, Brazil, show that the formation of weathering pro,les in these regions is contemporaneous, suggesting a strong weathering event in the Middle to Late Miocene (10,8 Ma). The preservation of these Miocene samples at or near the present surface suggests that either erosion rates have been very low in the region since the Miocene or that a much thicker weathering mantle was present in the region originally. Assuming a constant thickness of weathering pro,les in the region throughout the Tertiary, we may calculate weathering front propagation rates of 4,8 m Myr,1 during the past 10 Ma. Copyright © 2004 John Wiley & Sons, Ltd. [source] Tooth row counts, vicariance, and the distribution of the sand tiger shark Carcharias taurusECOGRAPHY, Issue 5 2003Luis O. Lucifora Geographic variation in tooth row counts among sand tiger sharks Carcharias taurus (Chondrichthyes), from the SW Atlantic, NW Atlantic and the East China Sea is analyzed in this paper. We found significant differences between sand tigers from the SW Atlantic (Southern Hemisphere population) and each of the other two (Northern Hemisphere) regions in the number of upper lateral tooth rows, and between individuals from the SW Atlantic and the East China Sea in the total number of upper tooth rows. Sand tiger sharks from the two Northern Hemisphere populations did not differ in any of the studied variables. Our results agree with comparisons of vertebral counts between sand tiger sharks from Southern and Northern Hemispheres. Both lines of evidence suggest that Southern and Northern Hemisphere populations of C. taurus were isolated to a larger extent than populations of the Northern Hemisphere. The fossil record of the genus Carcharias begins in the Early Cretaceous and C. taurus is certainly known since the Late Miocene. During the Miocene, the Tethys Sea separating northern and southern land masses was still present and it provided a continuous temperate shallow sea that could allow dispersal of sand tiger sharks along Northern Hemisphere seas. Independent observations on the distribution and evolutionary history of the genera Myripristis, Neoniphon, Sargocentron and Aphanius, and genetic studies on the temperate shark genus Mustelus that indicate a close relationship between the Indo-Pacific M. manazo and the Mediterranean M. asterias suggest that this hypothesis is plausible and deserves to be tested. [source] EVOLUTION OF SUBTERRANEAN DIVING BEETLES (COLEOPTERA: DYTISCIDAE HYDROPORINI, BIDESSINI) IN THE ARID ZONE OF AUSTRALIAEVOLUTION, Issue 12 2003Remko Leys Abstract Calcrete aquifers in arid inland Australia have recently been found to contain the world's most diverse assemblage of subterranean diving beetles (Coleoptera: Dytiscidae). In this study we test whether the adaptive shift hypothesis (ASH) or the climatic relict hypothesis (CRH) is the most likely mode of evolution for the Australian subterranean diving beetles by using a phylogeny based on two sequenced fragments of mitochondrial genes (CO1 and 16S-tRNA-ND1) and linearized using a relaxed molecular clock method. Most individual calcrete aquifers contain an assemblage of diving beetle species of distantly related lineages and/or a single pair of sister species that significantly differ in size and morphology. Evolutionary transitions from surface to subterranean life took place in a relatively small time frame between nine and four million years ago. Most of the variation in divergence times of the sympatric sister species is explained by the variation in latitude of the localities, which correlates with the onset of aridity from the north to the south and with an aridity maximum in the Early Pliocene (five mya). We conclude that individual calcrete aquifers were colonized by several distantly related diving beetle lineages. Several lines of evidence from molecular clock analyses support the CRH, indicating that all evolutionary transitions took place during the Late Miocene and Early Pliocene as a result of aridification. [source] Major neotectonic features of eastern Marmara region, Turkey: development of the Adapazar,,Karasu corridor and its tectonic significanceGEOLOGICAL JOURNAL, Issue 2 2004nç Yi Abstract Eastern Marmara region consists of three different morphotectonic units: Thrace,Kocaeli Peneplain (TKP) and Çamda,,Akçakoca Highland (ÇAH) in the north, and Armutlu,Almac,k Highland in the south of the North Anatolian Fault Zone (NAFZ). The geologic-morphologic data and seismic profiles from the Sakarya River offshore indicate that the boundary between the TKP in the west and ÇAH in the east is a previously unrecognized major NNE,SSW-trending strike-slip fault zone with reverse component. The fault zone is a distinct morphotectonic corridor herein named the Adapazar,,Karasu corridor (AKC) that runs along the Sakarya River Valley and extends to its submarine canyon along the southern margin of the Black Sea in the north. It formed as a transfer fault zone between the TKP and ÇAH during the Late Miocene; the former has been experiencing extensional forces and the latter compressional forces since then. East,West-trending segments of the NAFZ cuts the NE,SW-trending AKC and their activity has resulted in the formation of a distinct fault-bounded morphology, which is characterized by alternating E,W highlands and lowlands in the AKC. Furthermore, this activity has resulted in the downward motion of an ancient delta and submarine canyon of the Sakarya River in the northern block of the NAFZ below sea level so that the waters of the Black Sea invaded them. The NE,SW-trending faults in the AKC were reactivated with the development of the NAFZ in the Late Pliocene, which then caused block motions and microseismic activities throughout the AKC. Copyright © 2004 John Wiley & Sons, Ltd. [source] Insights into biaxial extensional tectonics: an examplefrom the Sand,kl, Graben, West Anatolia, TurkeyGEOLOGICAL JOURNAL, Issue 1 2003Mustafa Cihan Abstract West Anatolia, together with the Aegean Sea and the easternmost part of Europe, is one of the best examples of continental extensional tectonics. It is a complex area bounded by the Aegean,Cyprus Arc to the south and the North Anatolian Fault Zone (NAFZ) to the north. Within this complex and enigmatic framework, the Sand,kl, Graben (10,km wide, 30,km long) has formed at the eastern continuation of the Western Anatolian extensional province at the north-northwestward edge of the Isparta Angle. Recent studies have suggested that the horst,graben structures in West Anatolia formed in two distinct extensional phases. According to this model the first phase of extension commenced in the Early,Middle Miocene and the last, which is accepted as the onset of neotectonic regime, in Early Pliocene. However, it is controversial whether two-phase extension was separated by a short period of erosion or compression during Late Miocene,Early Pliocene. Both field observations and kinematic analysis imply that the Sand,kl, Graben has existed since the Late Pliocene, with biaxial extension on its margins which does not necessarily indicate rotation of regional stress distribution in time. Although the graben formed later in the neotectonic period, the commencement of extension in the area could be Early Pliocene (c. 5,Ma) following a severe but short time of erosion at the end of Late Miocene. The onset of the extensional regime might be due to the initiation of westward motion of Anatolian Platelet along the NAFZ that could be triggered by the higher rate of subduction at the east Aegean,Cyprus Arc in the south of the Aegean Sea. Copyright © 2003 John Wiley & Sons, Ltd. [source] The Romagna Apennines, Italy: an eroded duplexGEOLOGICAL JOURNAL, Issue 1 2001A. Cerrina Feroni Abstract The study of clast composition carried out on the alluvial gravels of the Romagna Apennines of northern Italy has provided evidence for an extensive covering of allochthonous units (Ligurian nappe and Epiligurian succession) above the Miocene foredeep deposits (Marnoso-Arenacea Formation), which has been subsequently eroded during the Late Miocene,Pleistocene uplift. This result is confirmed by the burial history outlined in the Marnoso-Arenacea Formation through vitrinite reflectance and apatite fission-track analyses. The Romagna Apennines represent, therefore, a regional tectonic window where the thrust system that displaced the Marnoso-Arenacea Formation crops out. The geometric relations between this thrust system and the basal thrust of the Ligurian nappe, exposed at the boundaries of the Romagna Apennines (Sillaro Zone and Val Marecchia klippe), are consistent with a duplex structure. Thus, the Romagna Apennines thrust system is an eroded duplex. The duplex roof-thrust corresponds to the surface of the synsedimentary overthrust of the Ligurian nappe on the Marnoso-Arenacea Formation; the floor-thrust is located in the pelagic pre-foredeep deposits (Schlier Formation). Copyright © 2001 John Wiley & Sons, Ltd. [source] Small mammal (rodents and lagomorphs) European biogeography from the Late Oligocene to the mid PlioceneGLOBAL ECOLOGY, Issue 4 2007Olivier Maridet ABSTRACT Aim, To analyse the fossil species assemblages of rodents and lagomorphs from the European Neogene in order to assess what factors control small mammal biogeography at a deep-time evolutionary time-scale. Location, Western Europe: 626 fossil-bearing localities located within 31 regions and distributed among 18 successive biochronological units ranging from c. 27 Ma (million years ago; Late Oligocene) to c. 3 Ma (mid Pliocene). Methods, Taxonomically homogenized pooled regional assemblages are compared using the Raup and Crick index of faunal similarity; then, the inferred similarity matrices are visualized as neighbour-joining trees and by projecting the statistically significant interregional similarities and dissimilarities onto palaeogeographical maps. The inferred biogeographical patterns are analysed and discussed in the light of known palaeogeographical and palaeoclimatic events. Results, Successive time intervals with distinct biogeographical contexts are identified. Prior to c. 18 Ma (Late Oligocene and Early Miocene), a relative faunal homogeneity (high interregional connectivity) is observed all over Europe, a time when major geographical barriers and a weak climatic gradient are known. Then, from the beginning of the Middle Miocene onwards, the biogeography is marked by a significant decrease in interregional faunal affinities which matches a drastic global climatic degradation and leads, in the Late Miocene (c. 11 Ma), to a marked latitudinal pattern of small mammal distribution. In spite of a short rehomogenization around the Miocene/Pliocene boundary (6,4 Ma), the biogeography of small mammals in the mid Pliocene (c. 3 Ma) finally closely reflects the extant situation. Main conclusions, The resulting biogeographical evolutionary scheme indicates that the extant endemic situation has deep historical roots corresponding to global tectonic and climatic events acting as primary drivers of long-term changes. The correlation of biogeographical events with climatic changes emphasizes the prevalent role of the climate over geography in generating heterogeneous biogeographical patterns at the continental scale. [source] Organic facies and geochemical aspects in Neogene neritic sediments of the Takafu syncline area of central Japan: Paleoenvironmental and sedimentological reconstructionsISLAND ARC, Issue 4 2006Ken Sawada Abstract Organic petrological observations of kerogen macerals and organic geochemical analyses of carbon isotopes of kerogen macerals and biomarkers were conducted on Neogene neritic sediments of the Takafu syncline area of central Japan. The Senmi, Sakainomiya and Lower Shigarami Formations in that area were deposited at the neritic provinces on the southern edge of the paleo-Japan Sea during the Late Miocene to Early Pliocene. Sedimentary organic matter in these formations was almost terrigenous in origin. Changes in kerogen maceral compositions reflect sedimentological and tectonic histories evaluated in previous studies from sedimentary facies and paleontology. It was found that carbon isotope ratios (,13C) of kerogen macerals increased from ,28, to ,25, from the Sakainomiya to the lower part of the Lower Shigarami Formations. The cause of that increase was presumably the expansion of C4 plants into southwest Japan. The timing was concordant with that of the expansion of C4 plant grasslands in East Asia. The oxicity (oxic to anoxic) conditions of sea bottoms evaluated from pristane/phytane ratios varied. Particularly, in the lower part of the Senmi Formation, layers in which no steroid biomarkers could be detected were found, and had presumably formed under oxic conditions when strong biodegradation had occurred. Concentrations of regular (C27,C29) steranes and dinosteranes were higher in the Sakainomiya and Lower Shigarami Formations. This indicates that dinoflagellates-dominant primary productions were higher at those stages. In addition, concentrations of diatomaceous biomarkers such as C26 norsterane increased from the Lower Shigarami Formation, thus adding diatoms to the major producers. Furthermore, similar associations between the increases of ,13C values of kerogen macerals and concentrations of diatomaceous biomarkers were observed in the Takafu syncline area. Thus, the expansion of C4 plants was possibly associated with the high production of diatom in the shallow-marine areas of the paleo-Japan Sea during the Neogene Period. [source] Pb, Nd, and Sr isotopic constraints on the origin of Miocene basaltic rocks from northeast Hokkaido, Japan: Implications for opening of the Kurile back-arc basinISLAND ARC, Issue 2 2000Yasuo Ikeda Abstract Late Miocene (7,9 Ma) basaltic rocks from the Monbetsu-Kamishihoro graben in northeast Hokkaido have chemical affinities to certain back-arc basin basalts (referred to herein as Hokkaido BABB). Pb-, Nd- and Sr-isotopic compositions of the Hokkaido BABB and arc-type volcanic rocks (11,13 Ma and 4,4.5 Ma) from the nearby region indicate mixing between the depleted mantle and an EM II-like enriched component (e.g. subducted pelagic sediment) in the magma generation. At a given 87Sr/86Sr, Hokkaido BABB have slightly lower 143Nd/144Nd and slightly less radiogenic 206Pb/204Pb compared with associated arc-type lavas, but both these suites are difficult to distinguish solely on the basis of isotopic compositions. These isotopic data indicate that while generation of the Hokkaido BABB involves smaller amounts of the EM II-like enriched component than do associated arc lavas, Hokkaido BABB are isotopically distinct from basalts produced at normal back-arc basin spreading centers. Instead, northeast Hokkaido BABB are more similar to basalts erupted during the initial rifting stage of back-arc basins. The Monbetsu-Kamishihoro graben may have developed in association with extension that formed the Kurile Basin, suggesting that opening of the basin continued until late Miocene (7,9 Ma). [source] Functional anatomy of the forelimb in Promegantereon* ogygia (Felidae, Machairodontinae, Smilodontini) from the Late Miocene of Spain and the origins of the sabre-toothed felid modelJOURNAL OF ANATOMY, Issue 3 2010Manuel J. Salesa Abstract We examine the functional anatomy of the forelimb in the primitive sabre-toothed cat Promegantereon ogygia in comparison with that of the extant pantherins, other felids and canids. The study reveals that this early machairodontine had already developed strong forelimbs and a short and robust thumb, a combination that probably allowed P. ogygia to exert relatively greater forces than extant pantherins. These features can be clearly related to the evolution of the sabre-toothed cat hunting method, in which the rapid killing of prey was achieved with a precise canine shear-bite to the throat. In this early sabre-toothed cat from the Late Miocene, the strong forelimbs and thumb were adapted to achieve the rapid immobilization of prey, thus decreasing the risk of injury and minimizing energy expenditure. We suggest that these were the major evolutionary pressures that led to the appearance of the sabre-toothed cat model from the primitive forms of the Middle Miocene, rather than the hunting of very large prey, although these adaptations reached their highest development in the more advanced sabre-toothed cats of the Plio-Pleistocene, such as Smilodon and Homotherium. Although having very different body proportions, these later animals developed such extremely powerful forelimbs that they were probably able to capture relatively larger prey than extant pantherins. [source] The effect of environmental diversification on species diversification in New Caledonian caddisflies (Insecta: Trichoptera: Hydropsychidae)JOURNAL OF BIOGEOGRAPHY, Issue 5 2010Marianne Espeland Abstract Aim, To test whether environmental diversification played a role in the diversification of the New Caledonian Hydropsychinae caddisflies. Location, New Caledonia, south-west Pacific. Methods, The phylogeny of the New Caledonian Hydropsychinae caddisflies was hypothesized using parsimony and Bayesian methods on molecular characters. The Bayesian analysis was the basis for a comparative analysis of the correlation between phylogeny and three environmental factors: geological substrate (ultrabasic, non-ultrabasic), elevation and precipitation. Phylogenetic divergence times were estimated using a relaxed clock method, and environmental factors were mapped onto a lineage-through-time plot to investigate the timing of environmental diversification in relation to species radiation. The correlation between rainfall and elevation was tested using independent contrasts, and the gamma statistic was calculated to infer the diversification pattern of the group. Results, The diversification of extant Orthopsyche,Caledopsyche species began in the Middle,Late Oligocene, when much of the island of New Caledonia was covered by ultrabasic substrate and mountain forming was prevalent. Most lineages originated in the Middle,Late Miocene, a period associated with long-term climate oscillation. Optimization of environmental factors on the phylogeny demonstrated that the New Caledonian Hydropsychinae group adapted to ultrabasic substrate early in its evolutionary history. The clade living mostly on ultrabasic substrate was far more species-rich than the clade living mostly on non-ultrabasic substrate. Elevation and rainfall were significantly correlated with each other. The lineage-through-time plot revealed that the main environmental diversification preceded species diversification. A constant speciation through time was rejected, and the negative gamma indicates that most of the diversification occurred early in the history of the clade. According to the inferred phylogeny, the genus Orthopsyche McFarlane is a synonym under Caledopsyche Kimmins, and Abacaria caledona Oláh & Barnard should also be included in Caledopsyche. Main conclusions, The age of the radiation does not support a vicariance origin of New Caledonian Hydropsychinae caddisflies. Environmental diversification pre-dates lineage diversification, and thus environmental heterogeneity potentially played a role in the diversification of the group, by providing a variety of fragmented habitats to disperse into, promoting speciation. The negative gamma indicates that the speciation rate slowed as niches started to fill. [source] Australian biogeographical connections and the phylogeny of large genera in the plant family MyrtaceaeJOURNAL OF BIOGEOGRAPHY, Issue 7 2003Pauline Y. Ladiges Abstract Aim To compare the phylogeny of the eucalypt and melaleuca groups with geological events and ages of fossils to discover the time frame of clade divergences. Location Australia, New Caledonia, New Guinea, Indonesian Archipelago. Methods We compare published molecular phylogenies of the eucalypt and melaleuca groups of the plant family Myrtaceae with geological history and known fossil records from the Cretaceous and Cenozoic. Results The Australasian eucalypt group includes seven genera, of which some are relictual rain forest taxa of restricted distribution and others are species-rich and widespread in drier environments. Based on molecular and morphological data, phylogenetic analyses of the eucalypt group have identified two major clades. The monotypic Arillastrum endemic to New Caledonia is related in one clade to the more species-rich Angophora, Corymbia and Eucalyptus that dominate the sclerophyll vegetation of Australia. Based on the time of rifting of New Caledonia from eastern Gondwana and the age of fossil eucalypt pollen, we argue that this clade extends back to the Late Cretaceous. The second clade includes three relictual rain forest taxa, with Allosyncarpia from Arnhem Land the sister taxon to Eucalyptopsis of New Guinea and the eastern Indonesian archipelago, and Stockwellia from the Atherton Tableland in north-east Queensland. As monsoonal, drier conditions evolved in northern Australia, Arnhem Land was isolated from the wet tropics to the east and north during the Oligocene, segregating ancestral rain forest biota. It is argued also that the distribution of species in Eucalyptopsis and Eucalyptus subgenus Symphyomyrtus endemic in areas north of the stable edge of the Australian continent, as far as Sulawesi and the southern Philippines, is related to the geological history of south-east Asia-Australasia. Colonization (dispersal) may have been aided by rafting on micro-continental fragments, by accretion of arc terranes onto New Guinea and by land brought into closer proximity during periods of low sea-level, from the Late Miocene and Pliocene. The phylogenetic position of the few northern, non-Australian species of Eucalyptus subgenus Symphyomyrtus suggests rapid radiation in the large Australian sister group(s) during this time frame. A similar pattern, connecting Australia and New Caledonia, is emerging from phylogenetic analysis of the Melaleuca group (Beaufortia suballiance) within Myrtaceae, with Melaleuca being polyphyletic. Main conclusion The eucalypt group is an old lineage extending back to the Late Cretaceous. Differentiation of clades is related to major geological and climatic events, including rifting of New Caledonia from eastern Gondwana, development of monsoonal and drier climates, collision of the northern edge of the Australian craton with island arcs and periods of low sea level. Vicariance events involve dispersal of biota. [source] Late Miocene,Pliocene eclogite facies metamorphism, D'Entrecasteaux Islands, SE Papua New GuineaJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2007B. D. MONTELEONE Abstract The D'Entrecasteaux Islands of south-eastern Papua New Guinea are active metamorphic core complexes that formed within a region where the plate tectonic regime has transitioned from subduction to rifting. While rapid, post 4 Myr exhumation and cooling of amphibolite and greenschist facies rocks that constitute the footwall of the crustal scale detachment fault system have been previously documented on Fergusson and Goodenough Islands of the D'Entrecasteaux chain, the timing of eclogite facies metamorphism in rocks of the footwall was unknown. Recent work revealed that at least one of the eclogite bodies formed during the Pliocene. We present combined in situ ion microprobe U,Pb age analyses of zircon from five variably retrogressed eclogite samples from Fergusson and Goodenough Islands that document Late Miocene,Pliocene (8,2 Ma) eclogite formation on these islands. Textural relationships and zircon,garnet rare earth element partition coefficients indicate that U,Pb ages constrain zircon crystallization under eclogite facies conditions in all samples. Results suggest westward younging of eclogite facies metamorphism from Fergusson to Goodenough Island. Present-day exposure of Late Miocene,Pliocene eclogites requires exhumation rates > 2.5 cm yr,1. [source] TIMING AND MODES OF DEFORMATION IN THE WESTERN SICILIAN THRUST SYSTEM, SOUTHERN ITALYJOURNAL OF PETROLEUM GEOLOGY, Issue 2 2001L. Tortorici Imbricate units in the western Sicilian fold-and-thrust belt originated on the southern continental margin of Neotethys, and were deformed during the Neogene-Recent in response to convergence between the African and European Plates. Neogene-Pleistocene synorogenic sediments, deposited in flexural foredeeps and satellite piggy-back basins, contain a record of the belt's evolution. Progressive migration of the thrust front southwards into the foreland has been documented, beginning in the Tortonian and continuing to the present-day particularly in western parts of the belt. In the eastern part, activity on Quaternary strike-slip fault zones has produced asymmetric flower structures and other interference structures. In this paper, we present two regional sections across the western Sicilian foreland-thrust belt system. These structural cross-sections extend down as far as the top of the Hercynian basement and integrate our field observations with previously-acquired well log, magnetic and seismic data. We show that complex interactions between the foreland-migrating thrust belt, which developed between the Late Miocene and the Pleistocene, and Pleistocene strike-slip faults led to the development of structural traps which constitute potential targets for hydrocarbon exploration. [source] Colonization by barnacles on fossil Clypeaster: an exceptional example of larval settlementLETHAIA, Issue 4 2008ANA G. SANTOS The presence of c. 1450 individuals of the balanid barnacle Balanus crenatus Bruguière encrusting the test of a clypeasteroid sea urchin from the Late Miocene of the Guadalquivir Basin (southwestern Spain) allows proposing a settlement pattern linked to the growth of the encrusting organism. The possible influence of dip angle was controlled by dividing the test into four concentric zones ranging from lowest margin to apex (0,15°, 15,30°, 30,50° and 0°). Contour diagrams were prepared to identify areas of highest barnacle density as well as size categories distribution in relationship to the pitch of the sea urchin test. The orientation of balanid tests was recorded and plotted on rose diagrams from 0° to 180°. Four size categories of barnacles were distinguished: (1) < 1 mm, (2) 1,2 mm, (3) 2,3 mm and (4) 3,4 mm; these correspond to a growth sequence ranging from post-larval forms to juveniles. Two areas of maximum settlement density are situated on the posterior margin of the test, on aboral as well as oral surfaces. The aboral surface shows the maximum number of barnacles. Two groups of individuals are defined on the basis of their location, that is, those encrusting the posterior medium part of the urchin, and those located on the anterior half. The results suggest that larval settlement was initially controlled by the availability of free space and afterwards by an intensification effect. Orientation and dip of the test may have played a secondary role in the settlement of the larvae. Substrate colonization seems to have been closely related to the biostratinomic history of the sea urchin test and although several scenarios are possible, our data are congruent with a synchronous settlement of both surfaces (aboral and oral) by one spat or several. [source] Comparative phylogeography of Ponto-Caspian mysid crustaceans: isolation and exchange among dynamic inland sea basinsMOLECULAR ECOLOGY, Issue 10 2006ASTA AUDZIJONYTE Abstract The distributions of many endemic Ponto-Caspian brackish-water taxa are subdivided among the Black, Azov and Caspian Sea basins and further among river estuaries. Of the two alternative views to explain the distributions, the relict school has claimed Tertiary fragmentation of the once contiguous range by emerging geographical and salinity barriers, whereas the immigration view has suggested recolonization of the westerly populations from the Caspian Sea after extirpation during Late Pleistocene environmental perturbations. A study of mitochondrial (COI) phylogeography of seven mysid crustacean taxa from the genera Limnomysis and Paramysis showed that both scenarios can be valid for different species. Four taxa had distinct lineages related to the major basin subdivision, but the lineage distributions and depths of divergence were not concordant. The data do not support a hypothesis of Late Miocene (10,5 Myr) vicariance; rather, range subdivisions and dispersal from and to the Caspian Sea seem to have occurred at different times throughout the Pleistocene. For example, in Paramysis lacustris each basin had an endemic clade 2,5% diverged from the others, whereas Paramysis kessleri from the southern Caspian and the western Black Sea were nearly identical. Species-specific ecological characteristics such as vagility and salinity tolerance seem to have played important roles in shaping the phylogeographic patterns. The mitochondrial data also suggested recent, human-mediated cryptic invasions of P. lacustris and Limnomysis benedeni from the Caspian to the Sea of Azov basin via the Volga-Don canal. Cryptic species-level subdivisions were recorded in populations attributed to Paramysis baeri, and possibly in P. lacustris. [source] Geology, Wall-rock Alteration and Vein Paragenesis of the Bilimoia Gold Deposit, Kainantu Metallogenic Region, Papua New GuineaRESOURCE GEOLOGY, Issue 3 2007Joseph Onglo Espi Abstract The Bilimoia deposit (2.23 Mt, 24 g/t Au), located in the eastern Central Mobile Belt of mainland Papua New Guinea, is composed of fault-hosted, NW,NNW-trending Irumafimpa,Kora and Judd,Upper Kora Au-quartz veins hosted by Middle,Late Triassic basement that was metamorphosed to medium-grade greenschist facies between Middle,Late Triassic and Early,Middle Jurassic. Mineralizing fluids were introduced during crustal thickening, rapid uplift, change of plate motions from oblique to orthogonal compression, active faulting and S3 and S4 events in an S1,S4 deformation sequence. The Bilimoia deposit is spatially and temporally related to I-type, early intermediate to felsic and late mafic intrusions emplaced in Late Miocene (9,7 Ma). Hydrothermal alteration and associated mineralization is divided into 10 main paragenetic stages: (1) chlorite,epidote-selvaged quartz,calcite,specularite vein; (2) local quartz,illite,pyrite alteration; (3) quartz,sericite,mariposite,fuchsite,pyrite wall-rock alteration that delimits the bounding shears; (4) finely banded, colloform-, crustiform- and cockade-textured and drusy quartz ± early wolframite ± late adularia; (5) hematite; (6) pyrite; (7) quartz ± amethyst-base metal sulfides; (8) quartz,chalcopyrite,bornite,Sn and Cu sulfides,Au tellurides and Te ± Bi ± Ag ± Cu ± Pb phases; (9) Fe ± Mn carbonates; and (10) supergene overprint. Fluid inclusions in stage 4 are characterized by low salinity (0.9,5.4 wt% NaCl equivalent), aqueous,carbonic fluids with total homogenization temperatures ranging from 210 to 330°C. Some of the inclusions that homogenized between 285 and 330°C host coexisting liquid- and vapor-rich (including carbonic) phases, suggesting phase separation. Fluid inclusions in quartz intergrown with wolframite have low salinity (0.9,1.2 wt% NaCl equivalent), aqueous,carbonic fluids at 240,260°C, defining the latter's depositional conditions. The ore fluids were derived from oxidized magmatic source initially contaminated by reduced basement rocks. Wall-rock alteration and involvement of circulating meteoric waters were dominant during the first three stages and early part of stage 4. Stage 5 hematite was deposited as a result of stage 4 phase separation or entrainment of oxygenated groundwater. Gold is associated with Te- and Bi-bearing minerals and mostly precipitated as gold-tellurides during stage 8. Gold deposition occurred below 350°C due to a change in the sulfidation and oxidation state of the fluids, depressurization and decreasing temperature and activities of sulfur and tellurium. Bisulfides are considered to be the main Au-transporting complexes. The Bilimoia deposit has affinities that are similar to many gold systems termed epizonal orogenic and intrusion-related. The current data allow us to classify the Bilimoia deposit as a fault-controlled, metamorphic-hosted, intrusion-related mesothermal to low sulfidation epithermal quartz,Au,Te,Bi vein system. [source] Tectonic vs. climate forcing in the Cenozoic sedimentary evolution of a foreland basin (Eastern Southalpine system, Italy)BASIN RESEARCH, Issue 6 2009N. Mancin ABSTRACT This paper discusses the Cenozoic interaction of regional tectonics and climate changes. These processes were responsible for mass flux from mountain belts to depositional basins in the eastern Alpine retro-foreland basin (Venetian,Friulian Basin). Our discussion is based on the depositional architecture and basin-scale depositional rate curves obtained from the decompacted thicknesses of stratigraphic units. We compare these data with the timing of tectonic deformation in the surrounding mountain ranges and the chronology of both long-term trends and short-term high-magnitude (,aberrant') episodes of climate change. Our results confirm that climate forcing (and especially aberrant episodes) impacted the depositional evolution of the basin, but that tectonics was the main factor driving sediment flux in the basin up to the Late Miocene. The depositional rate remained below 0.1 mm year,1 on average from the Eocene to the Miocene, peaking at around 0.36 mm year,1, during periods of maximum tectonic activity in the eastern Southern Alps. This dynamic strongly changed during the Pliocene,Pleistocene, when the basin-scale depositional rate increased to an average of 0.26 mm year,1 (Pliocene) and 0.73 mm year,1 (Pleistocene). This result fits nicely with the long-term global cooling trend recorded during this time interval. Nevertheless, we note that the timing of the observed increase may be connected with the presumed onset of major glaciations in the southern flank of the Alps (0.7,0.9 Ma), the acceleration of the global cooling trend (since 3,4 Ma) and climate variability (in terms of magnitude and frequency). All these factors suggest that combined high-frequency and high-magnitude cooling,warming cycles are particularly powerful in promoting erosion in mid-latitude mountain belts and therefore in increasing the sediment flux in foreland basins. [source] Cenozoic Stratigraphy Deformation History in the Central and Eastern of Qaidam Basin by the Balance Section Restoration and its ImplicationACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2009Dongliang LIU Abstract: The Qaidam Basin, located in the northern margin of the Qinghai,Tibet Plateau, is a large Mesozoic,Cenozoic basin, and bears huge thick Cenozoic strata. The geologic events of the Indian-Eurasian plate,plate collision since ,55 Ma have been well recorded. Based on the latest progress in high-resolution stratigraphy, a technique of balanced section was applied to six pieces of northeast-southwest geologic seismic profiles in the central and eastern of the Qaidam Basin to reconstruct the crustal shortening deformation history during the Cenozoic collision. The results show that the Qaidam Basin began to shorten deformation nearly synchronous to the early collision, manifesting as a weak compression, the deformation increased significantly during the Middle and Late Eocene, and then weakened slightly and began to accelerate rapidly since the Late Miocene, especially since the Quaternary, reflecting this powerful compressional deformation and rapid uplift of the northern Tibetan Plateau around the Qaidam Basin. [source] Characteristics of Overpressure Systems and Their Significance in Hydrocarbon Accumulation in the Yinggehai and Qiongdongnan Basins, ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2003XIE Xinong Abstract Overpressure systems are widely developed in the central depression and palco-uplift in the Yinggehai and Qiongdongnan basins. They can be divided into three types according to the origin of abnormally high formation pressure in the reservoirs, i.e. the autochthonous, vertically-transmitted and laterally-transmitted types. The autochthonous overpressure system results from rapid disequilibrium sediment loading and compaction. In the allochthonous overpressure system, the increase of fluid pressure in sandstone originates from the invasion of overpressured fluid flowing vertically or laterally through the conduit units. The autochthonous overpressure system occurs in the deep-lying strata of Neogene age in the central depression of the Yinggehai and Qiongdongnan basins. The vertically transmitted overpressure system is developed in the shallow strata of Late Miocene and Pliocene ages in the diapiric zone of the central Yinggehai basin, and the laterally transmitted overpressure system occurs in the Oligocene strata of paleo-uplifts, such as the structure of Ya-211 in the Qiongdongnan basin. The results indicate that the autochthonous overpressure system is generally a closed one, which is unfavorable for the migration and accumulation of hydrocarbons. In the allochthonous overpressure system, hydrocarbon accumulation depends on the relationship between the formation of overpressure systems and the spatial location and duration of hydrocarbon migration. The interval overlying the overpressure system is usually a favorable hydrocarbon accumulation zone if the duration of fluid expulsion coincides with that of hydrocarbon accumulation. [source] Climate cooling promoted the expansion and radiation of a threatened group of South American orchids (Epidendroideae: Laeliinae)BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2010ALEXANDRE ANTONELLI The Brazilian Cerrado is the most species-rich tropical savanna in the world. Within this biome, the Campos Rupestres (,rocky savannas') constitute a poorly studied and highly threatened ecosystem. To better understand how plants characteristic of this vegetation have evolved and come to occupy the now widely-separated patches of rocky formations in eastern Brazil, we reconstruct the biogeographical history of the rare orchid genus Hoffmannseggella. We apply parsimony and Bayesian methods to infer the phylogenetic relationships among 40 out of the 41 described species. Absolute divergence times are calculated under penalized likelihood and compared with estimates from a Bayesian relaxed clock. Ancestral ranges are inferred for all nodes of the phylogeny using Fitch optimization and statistical dispersal vicariance analysis. In all analyses, phylogenetic uncertainty is taken into account by the independent analysis of a large tree sample. The results obtained indicate that Hoffmannseggella underwent rapid radiation around the Middle/Late Miocene (approximately 11,14 Mya). The region corresponding today to southern Minas Gerais acted as a main source area for several independent range expansions north- and eastwards via episodic corridors. These results provide independent evidence that climate cooling following the Middle Miocene Climatic Optimum (approximately 15 Mya) led to important vegetational shifts in eastern Brazil, causing an increase in the dominance of open versus closed habitats. Polyploidy following secondary contact of previously isolated populations may have been responsible for the formation of many species, as demonstrated by the high ploidy levels reported in the genus. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 597,607. [source] Rudabánya: A late miocene subtropical swamp deposit with evidence of the origin of the African apes and humansEVOLUTIONARY ANTHROPOLOGY, Issue 2 2002László Kordos Abstract Rudabánya, a rich late Miocene fossil site in northern central Hungary, has yielded an abundant record of fossil primates, including the primitive catarrhine Anapithecus and the early great ape Dryopithecus. While the affinities of Anapithecus are not clear, Dryopithecus is clearly a great ape sharing numerous characteristics of its dental, cranial and postcranial anatomy with living great apes. Like all Miocene hominids (great apes and humans), Dryopithecus is more primitive in a number of ways than any living hominid, which is probably related to the passage of time since the divergence of the various lineages of living hominids, allowing for similar refinements in morphology and adaptation to take place independently. On the other hand, Dryopithecus (and Ouranopithecus) share derived characters with hominines (African apes and humans), and Sivapithecus (and Ankarapithecus) share derived characters with orangutans, thus dating the split between pongines and hominines to a time before the evolution of these fossil great apes. Pongines and hominines follow similar fates in the late Miocene, the pongines moving south into Southeast Asia from southern or eastern Asia and the hominines moving south into East Africa from the Mediterranean region, between 6 to 9 Ma. [source] SYNTHESIS: Evolutionary history of Pacific salmon in dynamic environmentsEVOLUTIONARY APPLICATIONS (ELECTRONIC), Issue 2 2008Robin S. Waples Abstract Contemporary evolution of Pacific salmon (Oncorhynchus spp.) is best viewed in the context of the evolutionary history of the species and the dynamic ecosystems they inhabit. Speciation was complete by the late Miocene, leaving c. six million years for intraspecific diversification. Following the most recent glacial maximum, large areas became available for recolonization. Current intraspecific diversity is thus the product of recent evolution overlaid onto divergent historical lineages forged during recurrent episodes of Pleistocene glaciation. In northwestern North America, dominant habitat features have been relatively stable for the past 5000 years, but salmon ecosystems remain dynamic because of disturbance regimes (volcanic eruptions, landslides, wildfires, floods, variations in marine and freshwater productivity) that occur on a variety of temporal and spatial scales. These disturbances both create selective pressures for adaptive responses by salmon and inhibit long-term divergence by periodically extirpating local populations and creating episodic dispersal events that erode emerging differences. Recent anthropogenic changes are replicated pervasively across the landscape and interrupt processes that allow natural habitat recovery. If anthropogenic changes can be shaped to produce disturbance regimes that more closely mimic (in both space and time) those under which the species evolved, Pacific salmon should be well-equipped to deal with future challenges, just as they have throughout their evolutionary history. [source] Ribosomal RNA gene fragments from fossilized cyanobacteria identified in primary gypsum from the late Miocene, ItalyGEOBIOLOGY, Issue 2 2010G. PANIERI Earth scientists have searched for signs of microscopic life in ancient samples of permafrost, ice, deep-sea sediments, amber, salt and chert. Until now, evidence of cyanobacteria has not been reported in any studies of ancient DNA older than a few thousand years. Here, we investigate morphologically, biochemically and genetically primary evaporites deposited in situ during the late Miocene (Messinian) Salinity Crisis from the north-eastern Apennines of Italy. The evaporites contain fossilized bacterial structures having identical morphological forms as modern microbes. We successfully extracted and amplified genetic material belonging to ancient cyanobacteria from gypsum crystals dating back to 5.910,5.816 Ma, when the Mediterranean became a giant hypersaline brine pool. This finding represents the oldest ancient cyanobacterial DNA to date. Our clone library and its phylogenetic comparison with present cyanobacterial populations point to a marine origin for the depositional basin. This investigation opens the possibility of including fossil cyanobacterial DNA into the palaeo-reconstruction of various environments and could also be used to quantify the ecological importance of cyanobacteria through geological time. These genetic markers serve as biosignatures providing important clues about ancient life and begin a new discussion concerning the debate on the origin of late Miocene evaporites in the Mediterranean. [source] A complex, young subduction zone imaged by three-dimensional seismic velocity, Fiordland, New ZealandGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001Donna Eberhart-Phillips Summary The Fiordland subduction zone, where subduction developed in the late Miocene, has been imaged with P and S,P arrival-time data from 311 earthquakes in a simultaneous inversion for hypocentres and 3-D VP and VP/VS models. The three-month microearthquake survey, recorded with 24 portable seismographs, provides excellent coverage, and, since earthquakes to depths of 130 km are included, parts of the model are well-resolved to depths of 100 km. The crustal features are generally consistent with geology. The low velocity in the upper 10 km is associated with the Te Anau and Waiau basins. The Western Fiordland Orthogneiss is associated with a prominent feature from near-surface to over 40 km depth, which includes the residue from the basaltic source rocks. It is defined by high VP (7.4 km s,1 at 15 km depth) and slightly low VP/VS, and has distinct boundaries on its southern and eastern margins. Adjacent to the deepest earthquakes, there is high-velocity Pacific mantle below 80 km depth, inferred to be the mantle expression of ongoing shortening since the early Miocene. As the subducting slab moves down and northeast, it is hindered by the high-velocity body and bends to near-vertical. Bending is accommodated by distributed fracturing evidenced by high VP/VS and persistent deep earthquake activity. Buckling of the subducted plate pushes up the Western Fiordland Orthogneiss. In the transition to the Alpine fault in northern Fiordland, a prominent low-velocity crustal root is consistent with ductile thickening in combination with downwarp of the subducted plate. [source] Tectonic control of erosion and sedimentation in the Amazon Basin of BoliviaHYDROLOGICAL PROCESSES, Issue 22 2009Patrice Baby Abstract The western Amazon drainage basin, which extends from southern Colombia to northern Bolivia, comprises the Cordillera Oriental of the Andes and its adjacent foreland basin system. In northern Bolivia, the orogenic wedge of the eastern Andes is very large, and its forward propagation controls the morphology of the Madeira drainage basin. We consider here the erosion and sedimentation mass balance in this part of the Amazon Basin, estimated on the basis of recent sediment yield data, within the current tectonic and geomorphic framework. The total suspended sediment (TSS) flux exported from the present orogenic wedge of northern Bolivia has been estimated at 500,600 million t year,1. More than 50% of the total sediment load crossing the Madeira foreland basin system is deposited. The rest of the sediments (less than 46%) reaches the eastern Amazon Basin, bypassing the Brazilian craton to the north. The average mass of sediment that has been deposited from the late Miocene to the present in the Madeira foreland basin sedimentation system is less than that intercepted today, by a factor of about 2·4. These results can be interpreted as an increase in Bolivian foreland basin flexural subsidence over time, associated with crust thickening and orogenic loading, and accentuated by the growing mass of retained sediments. They are consistent with the uplift rates of the Cordillera Oriental, obtained from fission-track dating, which began increasing significantly around 10,15 Ma. Copyright © 2009 John Wiley & Sons, Ltd. [source] Long-term changes in distribution and chemistry of middle Miocene to Quaternary volcanism in the Chokai-Kurikoma area across the Northeast Japan ArcISLAND ARC, Issue 1 2004Hirofumi Kondo Abstract To understand the characteristics of long-term spatial and temporal variation in volcanism within a volcanic arc undergoing constant subduction since the cessation of back-arc opening, a detailed investigation of middle Miocene to Quaternary volcanism was carried out within the Chokai-Kurikoma area of the Northeast Japan Arc. This study involved a survey of available literature, with new K,Ar and fission track dating, and chemical analyses. Since 14 Ma, volcanism has occurred within the Chokai-Kurikoma area in specific areas with a ,branch-like' pattern, showing an east,west trend. This is in marked contrast to the widespread distribution of volcanism with a north,south trend in the 20,14 Ma period. The east,west- trending ,branches' are characterized by regular intervals (50,100 km) of magmatism along the arc. These branches since 14 Ma are remarkably discrepant to the general northwest,southeast or north-northeast,south-southwest direction of the crustal structures that have controlled Neogene to Quaternary tectonic movements in northeast Japan. In addition, evidence indicating clustering and focusing of volcanism into smaller regions since 14 Ma was verified. Comparison of the distribution and chemistry of volcanic rocks for three principal volcanic stages (11,8, 6,3 and 2,0 Ma) revealed that widely but sparsely distributed volcanic rocks had almost the same level of alkali and incompatible element concentrations throughout the area (with the exception of Zr) in the 11,8 Ma stage. However, through the 6,3 Ma stage to the 2,0 Ma stage, the concentration level in the back-arc cluster increased, while that in the volcanic front cluster remained almost constant. Therefore, the degree of partial melting has decreased, most likely with a simultaneous increase in the depth of magma segregation within the back-arc zone, whereas within the volcanic front zone, the conditions of magma generation have changed little over the three stages. In conclusion, the evolution of the thermal structure within the mantle wedge across the arc since 14 Ma has reduced the extent of ascending mantle diapirs into smaller fields. This has resulted in the tendency for the distribution of volcanism to become localized and concentrated into more specific areas in the form of clusters from the late Miocene to Quaternary. [source] Pb, Nd, and Sr isotopic constraints on the origin of Miocene basaltic rocks from northeast Hokkaido, Japan: Implications for opening of the Kurile back-arc basinISLAND ARC, Issue 2 2000Yasuo Ikeda Abstract Late Miocene (7,9 Ma) basaltic rocks from the Monbetsu-Kamishihoro graben in northeast Hokkaido have chemical affinities to certain back-arc basin basalts (referred to herein as Hokkaido BABB). Pb-, Nd- and Sr-isotopic compositions of the Hokkaido BABB and arc-type volcanic rocks (11,13 Ma and 4,4.5 Ma) from the nearby region indicate mixing between the depleted mantle and an EM II-like enriched component (e.g. subducted pelagic sediment) in the magma generation. At a given 87Sr/86Sr, Hokkaido BABB have slightly lower 143Nd/144Nd and slightly less radiogenic 206Pb/204Pb compared with associated arc-type lavas, but both these suites are difficult to distinguish solely on the basis of isotopic compositions. These isotopic data indicate that while generation of the Hokkaido BABB involves smaller amounts of the EM II-like enriched component than do associated arc lavas, Hokkaido BABB are isotopically distinct from basalts produced at normal back-arc basin spreading centers. Instead, northeast Hokkaido BABB are more similar to basalts erupted during the initial rifting stage of back-arc basins. The Monbetsu-Kamishihoro graben may have developed in association with extension that formed the Kurile Basin, suggesting that opening of the basin continued until late Miocene (7,9 Ma). [source] Phylogeographic analysis detects congruent biogeographic patterns between a woodland agamid and Australian wet tropics taxa despite disparate evolutionary trajectoriesJOURNAL OF BIOGEOGRAPHY, Issue 8 2010Danielle L. Edwards Abstract Aim, To test the congruence of phylogeographic patterns and processes between a woodland agamid lizard (Diporiphora australis) and well-studied Australian wet tropics fauna. Specifically, to determine whether the biogeographic history of D. australis is more consistent with a history of vicariance, which is common in wet tropics fauna, or with a history of dispersal with expansion, which would be expected for species occupying woodland habitats that expanded with the increasingly drier conditions in eastern Australia during the Miocene,Pleistocene. Location, North-eastern Australia. Methods, Field-collected and museum tissue samples from across the entire distribution of D. australis were used to compile a comprehensive phylo-geographic dataset based on c. 1400 bp of mitochondrial DNA (mtDNA), incorporating the ND2 protein-coding gene. We used phylogenetic methods to assess biogeographic patterns within D. australis and relaxed molecular clock analyses were conducted to estimate divergence times. Hierarchical Shimodaira,Hasegawa tests were used to test alternative topologies representing vicariant, dispersal and mixed dispersal/vicariant biogeographic hypotheses. Phylogenetic analyses were combined with phylogeographic analyses to gain an insight into the evolutionary processes operating within D. australis. Results, Phylogenetic analyses identified six major mtDNA clades within D. australis, with phylogeographic patterns closely matching those seen in many wet tropics taxa. Congruent phylogeographic breaks were observed across the Black Mountain Corridor, Burdekin and St Lawrence Gaps. Divergence amongst clades was found to decrease in a north,south direction, with a trend of increasing population expansion in the south. Main conclusions, While phylogeographic patterns in D australis reflect those seen in many rain forest fauna of the wet tropics, the evolutionary processes underlying these patterns appear to be very different. Our results support a history of sequential colonization of D. australis from north to south across major biogeographic barriers from the late Miocene,Pleistocene. These patterns are most likely in response to expanding woodland habitats. Our results strengthen the data available for this iconic region in Australia by exploring the understudied woodland habitats. In addition, our study shows the importance of thorough investigations of not only the biogeographic patterns displayed by species but also the evolutionary processes underlying such patterns. [source] The antiquity of Madagascar's grasslands and the rise of C4 grassy biomesJOURNAL OF BIOGEOGRAPHY, Issue 10 2008William J. Bond Abstract Aim, Grasslands and savannas, which make up > 75% of Madagascar's land area, have long been viewed as anthropogenically derived after people settled on the island c. 2 ka. We investigated this hypothesis and an alternative , that the grasslands are an insular example of the post-Miocene spread of C4 grassy biomes world-wide. Location, Madagascar, southern Africa, East Africa. Methods, We compared the number of C4 grass genera in Madagascar with that in southern and south-central African floras. If the grasslands are recent we would expect to find fewer species and genera in Madagascar relative to Africa and for these species and genera to have very wide distribution ranges in Madagascar. Secondly, we searched Madagascan floras for the presence of endemic plant species or genera restricted to grasslands. We also searched for evidence of a grassland specialist fauna with species endemic to Madagascar. Plant and animal species endemic to C4 grassy biomes would not be expected if these are of recent origin. Results, Madagascar has c. 88 C4 grass genera, including six endemic genera. Excluding African genera with only one or two species, Madagascar has 86.6% of southern Africa's and 89.4% of south-central Africa's grass genera. C4 grass species make up c. 4% of the flora of both Madagascar and southern Africa and species : genus ratios are similar (4.3 and 5.1, respectively). Turnover of grasses along geographical gradients follows similar patterns to those in South Africa, with Andropogoneae dominating in mesic biomes and Chlorideae in semi-arid grassy biomes. At least 16 monocot genera have grassland members, many of which are endemic to Madagascar. Woody species in frequently burnt savannas include both Madagascan endemics and African species. A different woody flora, mostly endemic, occurs in less frequently burnt grasslands in the central highlands, filling a similar successional niche to montane C4 grasslands in Africa. Diverse vertebrate and invertebrate lineages have grassland specialists, including many endemic to Madagascar (e.g. termites, ants, lizards, snakes, birds and mammals). Grassland use of the extinct fauna is poorly known but carbon isotope analysis indicates that a hippo, two giant tortoises and one extinct lemur ate C4 or CAM (crassulacean acid metabolism) plants. Main conclusions, The diversity of C4 grass lineages in Madagascar relative to that in Africa, and the presence of plant and animal species endemic to Madagascan grassy biomes, does not fit the view that these grasslands are anthropogenically derived. We suggest that grasslands invaded Madagascar after the late Miocene, part of the world-wide expansion of C4 grassy biomes. Madagascar provides an interesting test case for biogeographical analysis of how these novel biomes assembled, and the sources of the flora and fauna that now occupy them. A necessary part of such an analysis would be to establish the pre-settlement extent of the C4 grassy biomes. Carbon isotope analysis of soil organic matter would be a feasible method for doing this. [source] | ||||||||||||||||||||||||||||