foot posture in a primitive pterosaur the nature of the hindlimb posture and gait of pterosaurs has been controversial1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 partly because most of the pterosaur skeletons that have been found were flattened in thin bedded rocks therefore obscuring three dimensional anatomy a major controversy concerns the extent to which pterosaurs move on the ground they have been variously interpreted as ranging from sprawling quadrupedal walkers to erect bird like bipedal cursors1 study of pelvis and femur material from the derived group pterodactyloidea11 12 13 has resolved which movements are possible at the hip but the lack of three dimensional articulated pterosaur feet has prevented examination of all of the movements that are possible within the foot we have found a large uncrushed partial skeleton of a new species of the basal pterosaur dimorphodon in thick bedded deposits of tamaulipas mexico this material includes such a three dimensional foot the nature of this skeleton contradicts an important part of the cursorial interpretation that is that only the toes contacted the ground during terrestrial locomotion2 3 4 5 6 7 the flattened metatarsal phalangeal joint at the base of the first four toes of this specimen would not allow such a digitigrade posture without separating most of the joints a flat footed stance is consistent with presumed footprints of pterosaurs8 9 10 that show impressions of the entire sole of the foot

an analysis of the ice sheet surface and subsurface topography above the vostok station subglacial lake central east antarctica radio echo sounding res and satellite radar altimeter data were analyzed in order to identify the surface and subsurface topography around the largest known subglacial lake at vostok station east antarctica named here as lake vostok in doing so a data set was established from which a qualitative description of the flow of ice across the lake was developed patterns of ice flow were constructed through consideration of 1 the ice sheet surface from the satellite altimeter and 2 internal layering from res it is concluded that lake vostok influences the dynamics of the overriding ice specifically although the flow of ice across the lake is dominated by the general eastward flow of the grounded ice sheet a southward velocity component caused by an ice shelf type ice flow mechanism is also present over the subglacial lake a further 67 smaller subglacial lakes exist within central regions of the antarctic ice sheet occupying 5 10 of the ice sheet base subglacial lakes may therefore exert a significant control on ice dynamics within central antarctica

ichnological evidence for quadrupedal locomotion in pterodactyloid pterosaurs trackways from the late jurassic of crayssac southwestern france abstract more than 30 well preserved pterosaurian trackways have been excavated from the site of crayssac lower tithonian southwestern france along with hundreds of isolated imprints the general pattern of pterosaurian trackways is described and corresponds to the morphology of the ichnogenus pteraichnus stokes 1957 a crocodilian origin for pteraichnus is rejected the morphology of the pes and manus prints is described and discussed and exhibits a great dynamic variability the three manus digit prints are confirmed as the marks of digits i iii but the high angle of divarication may reflect strong digit abduction as well as a backward folding of the digit iii the manus gait width is as much as 3 the pes gait width the narrowest manus trackways corresponds to low velocity walking in a semi erect stance whereas the widest manus trackways corresponds to higher velocity walking perhaps even running with a subhorizontal body

the hydrochemistry of lake vostok and the potential for life in antarctic subglacial lakes our understanding of lake vostok the huge subglacial lake beneath the east antarctic ice sheet has improved recently through the identification of key physical and chemical interactions between the ice sheet and the lake the north of the lake where the overlying ice sheet is thickest is characterized by subglacial melting whereas freezing of lake water occurs in the south resulting in 210 m of ice accretion to the underside of the ice sheet the accreted ice contains lower concentrations of the impurities normally found in glacier ice suggesting a net transfer of material from meltwater into the lake the small numbers of microbes found so far within the accreted ice have dna profiles similar to those of contemporary surface microbes microbiologists expect however that lake vostok and other subglacial lakes will harbour unique species particularly within the deeper waters and associated sediments the extreme environments of subglacial lakes are characterized by high pressures low temperatures permanent darkness limited nutrient availability and oxygen concentrations that are derived from the ice that provides the meltwater copyright 2002 john wiley sons ltd

a large deep freshwater lake beneath the ice of central east antarctica in 1974 75 an airborne radio echo survey of ice depths over central east antarctica led to the discovery of a sub ice lake of unknown depth and composition with an area of about 10 000km2 and lying beneath 4km of ice1 in 1993 altimetric data from satellite measurements2 provided independent evidence of the lake s areal extent thus confirming it to be the largest known sub ice lake by an order of magnitude here we analyse new altimetric and radio echo data along with existing seismic data3 to show that the lake is deep mean depth of 125 m or more and fresh and that it has an area that exceeds previous estimates by about 50 dimensions comparable with those of lake ontario we estimate that the residence time of the water in the lake is of the order of tens of thousands of years and that the mean age of water in the lake since deposition as surface ice is about one million years regional ice dynamics can be explained in terms of steady state ice flow along and over the lake

identification of subglacial lakes using ers 1 radar altimeter radar altimeter data from ers 1 allow detailed topographic mapping of antarctica to 82 degrees s to be carried out revealing several notable surface features among these is the large subglacial lake near vostok which is mapped here in detail the central part of the lake is found to have an exceptionally smooth surface with r m s elevation variations of less than 0 2 m a search for other large antarctic lakes in the data is made based on the smoothness and low gradient of the surface a number of other flat areas are identified with lake locations previously determined from radio echo sounding observations however radar altimeter observations show that a minimum lake size of 20 km is required for a surface above a lake to become flat numerous bowl like features can be seen in the surface topography and these may be associated with intermediate sized subglacial lakes it is determined that high spatial resolution radar altimetery could be used to identify subglacial lakes greater than 10 km in lateral extent flat regions of the ice sheet are particularly useful as they may be used as height reference surfaces to help fix the orbits of radar altimeter satellites

sordes pilosus and the nature of the pterosaur flight apparatus it is now generally accepted that pterosaurs mesozoic reptiles were true fliers but the nature of their flight apparatus is still much disputed evidence has been presented in favour of bird like reconstructions with narrow stiff wings free of the legs1 6 and bat like reconstructions with extensive wings incorporating both fore and hind limbs7 10 but the solnhofen limestone pterosaurs upon which these models are based are not sufficiently well preserved to resolve these conflicting interpretations here we present a new model founded on sordes pilosus from the jurassic of middle asia ref 11 and n n b and d m u manuscript submitted in which exceptionally well preserved wing membranes show that the hind limbs of pterosaurs were intimately involved in the flight apparatus connected externally to the main wing membrane and internally by a uropatagium controlled by the fifth toe sordes also reveals that uniquely among flying vertebrates pterosaurs had a structurally non homogenous flight surface with a stiffened outer half and a softer more extensible inner region

a comparison of the performance of the ice and ocean tracking modes of the ers 1 radar altimeter over non ocean surfaces the european space agency s ers 1 radar altimeter is the first to include separate operating modes to optimise performance over both ocean and non ocean surfaces as part of the ers 1 commissioning activities we have carried out a study of the tracking performance of this instrument over non ocean surfaces statistics for land ice sea ice arid lands and inland water are presented performance in both operating modes is shown to be better than that of previous missions

seismic modelling study of a subglacial lake we characterize the seismic response of lake vostok an antarctic subglacial lake located at nearly 4 km depth below the ice sheet this study is relevant for the determination of the location and morphology of subglacial lakes the characterization requires the design of a methodology based on rock physics and numerical modelling of wave propagation the methodology involves rock physics models of the shallow layer firn the ice sheet and the lake sediments numerical simulation of synthetic seismograms ray tracing p transforms and ava analysis based on the theoretical reflection coefficients the modelled reflection seismograms show a set of straight events refractions through the firn and top ice layer and the two reflection events associated with the top and bottom of the lake theoretical ava analysis of these reflections indicates that at near offsets the pp wave anomaly is negative for the ice water interface and constant for the water sediment interface this behaviour is shown by ava analysis of the synthetic data set this study shows that subglacial lakes can be identified by using seismic methods moreover the methodology provides a tool for designing suitable seismic surveys

modeling the densification of polar firn including heat diffusion application to close off characteristics and gas isotopic fractionation for antarctica and greenland sites 1 modeling the densification of polar firn is essential to estimate variations of close off characteristics density close off depth delta age in relation with past climate parameters temperature and accumulation rates furthermore the air composition in the firn is modified by gravitational and thermal fractionation and stable isotope measurements of permanent gases like nitrogen or argon can provide information on the amplitude of these fractionations in this work we propose a new model coupling firn densification and heat diffusion in addition to the determination of the firn thickness and gas ice age differences the model allows a reconstruction of the time evolution of the temperature for different sites in antarctica vostok and greenland gisp2 and therefore the evolution of gravitational and thermal isotopic fractionations in firn under present day conditions the modeled profiles are in good agreement with the available temperature measurements in firn for sites with low accumulation rates such as vostok the results show the existence of temperature gradients in the firn column even when no rapid climatic changes occur the comparison of the modeled 15n results to measurements allows to better constrain the 18o temperature relationship used to infer the surface temperature history and for gisp2 the model validates the long term borehole based temperature

a new three dimensional higher order thermomechanical ice sheet model basic sensitivity ice stream development and ice flow across subglacial lakes 1 a new three dimensional thermomechanically coupled ice sheet model is developed contrary to the majority of three dimensional ice sheet models shallow ice approximation higher order stress gradients longitudinal and transverse are accounted for in the force balance equations the horizontal velocity field is determined from the force balance equations in their derivative form elliptical equation using the method presented by pattyn 2000 2002a the model is solved on a regular grid in the horizontal and an irregular grid in the vertical and is numerically stable basic experiments include the european ice sheet modeling initiative eismint benchmarks for largescale ice sheet models and a comparison with the saito blatter ice sheet model including higher order stress gradients saito et al 2003 detailed calculations of ice flow over three dimensional bedrock perturbations showed the validity of the higher order solution the model is capable of simulating the evolution of an ice stream within the ice sheet and shows important aspects of observed ice stream features such as the surface flattening and the importance of side drag the simulation of the ice flow over a subglacial lake results in a flattening of the surface a local velocity increase over the lake and a deviation of the ice flow from the main flow direction features which are also observed at lake vostok antarctica index terms 1827 hydrology glaciology 1863 1863 hydrology snow and ice 1827 3230 mathematical geophysics numerical solutions keywords higher order ice sheet model thermomechanical ice stream subglacial lake citation pattyn f a new three dimensional higher order thermomechanical ice sheet model basic sensitivity ice stream development and ice flow across subglacial lakes j geophys res 108 b8 2382 doi 10 1029 2002jb002329 2003

exceptionally well preserved pterosaur wing membrane from the cretaceous of brazil fossilized impressions of pterosaur wing membranes are known from a number of localities1 2 but true soft tissue preservation is extremely rare3 4 we present the first description of the internal anatomy of the wing membrane based on exceptionally well preserved soft tissues from the forearm of a lower cretaceous brazilian pterosaur a thin epidermis overlies a dermis composed successively of a stratum vasculosum stratum spongiosum and a layer of striated muscle this exceptional specimen provides important new insights into pterosaur biology incipient wrinkles and an apparent lack of stiffening fibres suggest the proximal region of the wing membrane was thin extensible and tensioned by the hind limb5 6 excess metabolic heat resulting from rigorous activity could be lost by vasodilation of the vascular layer a mechanism consistent with active flight in pterosaurs7 9

modelling accreted ice in subglacial lake vostok antarctica 1 the distribution and thickness of accreted ice at the ice lake interface of subglacial lake vostok east antarctica is calculated conflating various sources 1 the modelled basal mass balance at the ice lake interface based on two different bathymetry models 2 different ice flow trajectories obtained from satellite interferometry and ice penetrating radar measurements and 3 reasonable ice flow velocity our results show that the accreted ice distribution is highly sensitive to the ice draft and to the used flow line directions the volume and thickness of the accreted ice depends significantly on the ice flow velocity according to our modelling we estimate the accreted ice area volume and mean thickness to be 10 800 500 km2 980 200 km3 and 90 45 m respectively for an ice flow velocity of 3 6 m a only about 36 2 of lake vostok s surface is in contact with meteoric ice melted by about 2 65 0 10 cm a this has impacts on the sedimentation rate and the supply of nutrients oxygen and or other components only present in meteoric ice but not in accreted lake ice we estimate the residence time of the lake water at about 32 000 4000 years

airborne radar survey above vostok region east central antarctica ice thickness and lake vostok geometry during the 1999 2000 italian expedition an airborne radar survey was performed along 12 transects across lake vostok antarctica and its western and eastern margins ice thickness subglacial elevation and the precise location of lake boundaries were determined radar data confirm the geometry derived from previous surveys but with some slight differences we measured a length of up to 260 km a maximum width of 81 km and an area of roughly 14 000 km 2 along the major axis from north to south the ice thickness varies from 3800 to 4250 m with a decreasing gradient from west to east the ice thickness is fairly constant except for two narrow strips located on the western and eastern margins where it increases with high thickening rate over the lake the surface elevation increases from 3476 m a s l south to 3525 north with a decreasing gradient while the lake surface elevation decreases from 315 to 750 m a s l with a decreasing gradient absolute value the ice surface and lake ceiling slopes suggest that the lake is in a state of hydrostatic equilibrium

pterosaur track assemblages from the upper jurassic lower kimmeridgian intertidal deposits of poland linking ichnites to potential trackmakers abstract two distinct tetrapod track assemblages dominated by pterosaur traces are reported from upper jurassic lower kimmeridgian hypselocyclum zone tidal flat carbonate deposits exposed in wierzbica quarry 20 km south of radom poland the pterosaur tracks tentatively assigned to pteraichnus isp are well preserved as a positive hyporelief in intertidal facies some are preserved with anatomical details e g skin claw or digital pad impressions and quality sufficient to make preliminary ichnotaxonomic assignment nearly all collected specimens are larger than most other pterosaurian ichnites of the late jurassic age thus adding to the growing diversity of pterosaur traces known from this time period morphometrical and anatomical analyses show that ctenochasmatoids or possibly non pterydactyloid monofenestratans or rhamphorhynchids were most likely the trackmakers anatomical comparisons give new insights into the morphology of the pes of pterydactyloids and the most closely related non pterodactyloids which may be correlated with a niche expansion into marginal marine and lacustrine environments by middle and late jurassic pterosaurs the palaeoenvironmental interpretation as tidal flat is confirmed by presence of vertically accreted tidal bundles each representing deposition in one tidal cycle most likely then this was one of the environments frequented by these pterosaurs and other small tetrapods the wider palaeoecological significance of the tracks is evaluated in the context of other similar reports from the late jurassic of europe africa and north america

determining basal ice sheet conditions in the dome c region of east antarctica using satellite radar altimetry and airborne radio echo sounding large subglacial lakes manifest themselves as flat regions on the ice surface ers 1 satellite radar altimetry of the dome c region of east antarctica was analyzed to correlate unusually flat areas on the ice surface with known locations of subglacial lakes identified from airborne radio echo sounding res data the mean length of subglacial lakes which have an expression in the ice sheet surface was 8 3 km whilst those that did not exhibit a surface morphological manifestation had a mean length of 3 3 km thus lakes up to about 4 km in length are unlikely to be detected from satellite radar altimetry of the ice surface given that the spacing of radio echo flight tracks within the spri nsf tud antarctic database is 50 100 km in many areas a number ofsubglacial lakes probably lie undetected beneath the ice sheet res information from two large flat surface regions within dome c and a further flat area located at 80 s 127 e indicates the absence ofsubglacial lakes beneath the ice surface features however these areas are characterised by relatively strong radio echo returns which may indicate the presence of water saturated basal sediments we suggest that 1 blankets of water saturated basal sediments may cause similar surface morphological features to those produced by subglacial lakes and 2 misidentification ofsubglacial lakes from satellite altimeter observations of the ice sheet surface is possible without the support of res information relating to the ice sheet base furthermore our study indicates a lack of sub glacial lake signals from res data over relatively thick regions of east antarctica such as the adventure subglacial trough we conclude that subglacial water produced in such regions may be transported by a basal hydrological system driven by overburden pressure to less thick regions of the ice sheet where subglacial lakes have been identified

distribution of isolated volcanoes on the flanks of the east pacific rise 15 3 s 20 s volcanic constructions not associated with seamount or volcano chains are abundant on the flanks of the east pacific rise epr but are rare along the axial high the distribution of isolated volcanoes based on multibeam bathymetric maps is approximately symmetric about the epr axis this symmetry contrasts with the asymmetries in the distribution of volcano chains more abundant on the west flank the seafloor subsidence rates slower on the west flank and the distribution of plate motion parallel gravity lineaments more prominent on the west flank most of the isolated volcanoes complete their growth within 14 km of the axis on crust younger than 0 2 ma while seamount chain volcanoes continue to be active on older crust volcanic edifices within 6 km of the ridge axis are primarily found adjacent to axial discontinuities suggesting a more sporadic magma supply and stronger lithosphere able to support volcanic constructions near axial discontinuities the volume of isolated near axis volcanoes correlates with ridge axis cross sectional area suggesting a link between the magma budget of the ridge and the eruption of near axis volcanoes within the study area off axis volcanic edifices cover at least 6 of the seafloor and contribute more than 0 2 to the volume of the crust the inferred width of the zone where isolated volcanoes initially form increases with spreading rate for the mid atlantic ridge 4 km northern epr 20 km and southern epr 28 km so that isolated volcanoes form primarily on lithosphere younger than 0 2 ma 4 6 km brittle thickness independent of spreading rate this suggests some form of lithospheric control on the eruption of isolated off axis volcanoes due to brittle thickness increased normal stresses across cracks impeding dike injection or thermal stresses within the newly forming lithosphere

the response of the subglacial lake vostok antarctica to tidal and atmospheric pressure forcing summary lake vostok is the largest subglacial lake in antarctica we show that as a result of its size tidal and atmospheric pressure forcings are large enough to induce vertical displacements of the ice surface above the lake these effects have been modelled assuming equilibrium tides and an inverse barometer response based on mass conservation differences in the tidal potential on the area of the lake result in height changes with amplitudes of a few millimetres for the largest diurnal and semidiurnal tides with maximum values at the southern end of the lake air pressure differences above the lake cause a differential inverse barometer effect ibe with resulting height changes of up to 40 mm on timescales from days to weeks both effects could be verified by differential global positioning system gps observations in the southern part of the lake during the 2001 2002 and 2002 2003 summer seasons the measured amplitudes and phases of the main constituents correspond to the respective values of the differential equilibrium tides ers 1 2 tandem interferograms of 1996 were used to analyse the spatial pattern of the surface displacement for the southern part of the lake these measurements reveal a bulge with a wide flexure zone of varying amplitude but a similar geometry a quasi simultaneous pair of interferograms from the northern and the southern part of the lake respectively demonstrates surface height changes of opposite sign in both areas therefore it can be concluded that the associated water redistribution as a result of tides and changing atmospheric pressure forms an additional component of the overall water circulation in the lake

radio echo layering in polar ice sheets and past volcanic activity a recent study1 has shown how acidity profiles along dated greenland ice cores can reveal large volcanic eruptions in the northern hemisphere during the past 10 000 yr it has been suggested that these layers of acidic ice in the polar ice sheets may also be detected by airborne radio echo sounding res techniques as stratification echoes2 4 explosive volcanic eruptions eject large amounts of so2 into the stratosphere5 where it forms an h2so4 aerosol6 studies of antarctic snow7 and greenland ice cores2 show that this material can be deposited in layers of large areal extent on polar ice sheets calculations based on observations of these slightly acidic layers show that they should give rise to radar reflections of similar magnitude to those observed for stratification echoes new res data from the antarctic enables the present comparison to be made between observed layer power reflection coefficients prcs and calculated values for reflections from acidic ice layers and from layers of ice of changed density a gap in layering has been identified which seems to coincide with a similar gap reported in greenland at crete8 profiles of layer prc against age show a common pattern for many sites on the antarctic ice sheet this prc age profile may provide a record of explosive volcanic activity for the southern hemisphere over the past 150 000 yr

the origin of endothermy in synapsids and archosaurs and arms races in the triassic abstract birds and mammals are key elements of modern ecosystems and many biologists explain their great success by their endothermy or warm bloodedness new palaeontological discoveries point to the origins of endothermy in the triassic and that birds archosaurs and mammals synapsids likely acquired endothermy in parallel here a further case is made that the emergence of endothermy in a stepwise manner began in the late permian but accelerated in the early triassic the trigger was the profound destruction wrought by the permian triassic mass extinction ptme in the oceans this was the beginning of the mesozoic marine revolution mmr and a similar revolution occurred on land termed here the triassic terrestrial revolution ttr among tetrapods both synapsids and archosaurs survived into the triassic but numbers were heavily depleted however the survivors were marked by the acquisition of endothermy as shown by bone histology isotopic analyses and the acquisition of insulating pelage both groups before the ptme had been sprawlers after the event they adopted parasagittal erect gait the new posture and the new physiology enabled both groups to compete in their ecosystems at a faster rate than before the ptme the new world of the triassic was characterised by a fast paced arms race between synapsids and archosauromorphs in which the latter as both dinosaurs and pterosaurs initially prevailed

water exchange between the subglacial lake vostok and the overlying ice sheet it has now been known for several years that a 200 km long lake called lake vostok lies beneath the ice sheet on which sits vostok station in antarctica the conditions at the base of the ice sheet above this subglacial lake can provide information about the environment within the lake including the likelihood that it supports life here we present an analysis of the ice sheet structure from airborne 60 mhz radar studies which indicates that distinct zones of basal ice loss and accretion occur at the ice water interface subglacial melting and net ice loss occur in the north of the lake and across its 200 km long western margin whereas about 150 m of ice is gained by subglacial freezing in the south this indicates that significant quantities of water are exchanged between the base of the ice sheet and the lake waters which will enrich the lake with gas hydrates cause sediment deposition and encourage circulation of the lake water