the terrestrial permian triassic boundary event bed is a nonevent comment we welcome the fact that gastaldo et al 2009 1 have been continuing research in the karoo of south africa those of us who have worked there know how important new research in this area is if we are to ever understand the causes of the permian triassic mass extinction on land however here

changing fluvial environments across the permian triassic boundary in the karoo basin south africa and possible causes of tetrapod extinctions abstract the karoo supergroup is a 12 km thick succession of sedimentary rocks that accumulated in a large intracratonic retroarc foreland basin in southwestern gondwana the strata record 100 million years of almost continuous sediment accumulation from the permo carboniferous 300 ma through to the early jurassic 190 ma under a range of climatic regimes and within several tectonically controlled sub basins alluvial sediments dominate the succession from the late permian onwards fossils of synapsid reptiles and early dinosaurs are sufficiently common to be used in a ten fold biostratigraphic subdivision of these strata the permian triassic boundary in the karoo succession is marked by a major extinction of the herbivorous dicynodonts which co incides with a rapid change in fluvial facies this study uses field observations of the sedimentary facies palaeosols and in situ fossils of well exposed p tr boundary sequences in the southern karoo basin to provide evidence of environmental changes that may have caused the tetrapod extinctions in the main karoo basin below the p tr boundary sequence the sediments comprise drab greenish grey mudrocks with a few thick 3 12 m multistoried laterally accreted fine grained sandstone bodies the mudrocks host hydromorphic palaeosols with palustrine carbonate horizons and mostly disarticulated skeletal remains of dicynodon assemblage zone fauna above a transition zone of approximately 20 m thickness these strata change into reddish brown mudrocks with numerous thin 0 5 5 m ribbon sandstone bodies and more continuous sheet sandstones calcic palaeosols with rhizocretions nodular horizons and pervasive calcareous encrustation of articulated skeletons of lystrosaurus and associated fauna of the lystrosaurus assemblage zone within a 20 m thick interval of the transitional strata fossils of dicynodon and lystrosaurus occur together the facies transition that co incides with the latest permian dicynodont extinction is interpreted as a change in fluvial style from meandering to low sinuosity channels with general drying of the floodplain habitats and redistribution of vegetation belts the horsetails in particular became significantly reduced in areal distribution the changes in fluvial style in the karoo basin at the end of the permian were triggered by a pulse of thrusting in the southerly source area dated at 247 ma 2 ma which brought about rapid progradation of a large sandy braided fan system the katberg sandstone fm into the central parts of the basin a concomitant basinward migration of depositional environments allowed the lystrosaurus communities that were adapted to dry floodplains to colonise the entire basin to the detriment of most of the wet floodplain dicynodon fauna that lived there

fungal abundance spike and the permian triassic boundary in the karoo supergroup south africa the most severe mass extinction of marine species and terrestrial vertebrates and plants is associated with the permian triassic boundary 251 ma the extinction interval is also marked by the disappearance of most late permian gymnosperm palynomorphs at a layer containing solely the abundant remains of fungi this fungal spike apparently represents widespread devastation of arboreous vegetation stratigraphic and palynological study of the carlton heights section in the southern karoo basin of south africa revealed a 1 m thick fungal spike zone that occurs simultaneously with the last appearance of typically late permian gymnosperm pollen the plant extinction and fungal spike zone are found above the last occurrence of late permian mammal like reptiles of the dicynodont zone at other karoo sections using the fungal event as a time line in marine and non marine sections allows placement of the marine extinctions and the extinction of terrestrial plants and reptiles within a brief crisis interval of less than about 40 000 years at the end of the permian

stability of polar frosts in spherical bowl shaped craters on the moon mercury and mars following svitek martian water frost control of global distribution by small scale processes ph d thesis california institute of technology 1992 analytic solutions are presented for the effective albedo the effective emissivity and the radiative equilibrium temperature in the shadowed portions of a spherical bowl shaped crater the model assumes that the surface is a lambert scatterer with visual albedo and infrared emissivity each independent of wavelength across their respective spectral ranges absorption emission and multiple scattering from the walls of the crater are treated rigorously to all orders for airless bodies whose surfaces are in radiative equilibrium all shadowed portions of any individual crater have the same temperature whose value depends on four quantities the insolation product of the solar constant and the sine of the solar elevation angle the depth diameter ratio of the crater the visual albedo and the infrared emissivity as long as the crater is deep enough to have shadows the lowest temperatures are for the shallowest crater those with the smallest depth diameter ratio the model is applied first to the moon and mercury using a depth diameter ratio of 0 2 which is typical of the lunar highlands according to pike geophys res lett 1 291 294 1974 in impact and explosion cratering roddy et al eds pp 489 509 pergamon new york 1977 for mercury and the moon temperatures in shadows in polar craters are below 102 k so the sublimation rate of water ice calculated according to the model of watson et al j geophys res 66 3033 3015 1961 is less than 1 cm per byr the latitudinal extent of the cold zone on the moon is greater than that on mercury although temperatures at the poles of the two planets are similar the other application is to polar frosts on mars illuminated water frosts in radiative equilibrium grow rougher because the average temperature of a depression is greater than that of flat ground subliming co 2 frosts which are always at the same temperature grow rougher at low solar elevation angles because the heat flux absorbed by a depression is greater than that for a flat surface at high insolation rates high sun near perihelion the average heat flux to a depression is less than for a flat surface the latter evaporates faster which makes the average surface smoother and leads to a high average albedo this behavior helps explain the fact that the south co 2 cap which receives its greatest insolation near perihelion has a higher effective albedo and therefore can survive the summer whereas the north co 2 cap has a lower effective albedo and disappears each year around summer solstice

geochemistry and age of timiskaming alkali volcanics and the otto syenite stock abitibi ontario tephrites and trachytes of the timiskaming volcanics from the kirkland lake area ontario and syenites and a granite from the nearby otto stock are characterized by extreme enrichment of incompatible elements coupled with relative depletion of nb ti and to a lesser extent zr and y the volcanic rocks have a whole rock sm nd isochron age of 2740 117 ma 2 error and minerals separated from the otto stock a sm nd age of 2544 50 ma conventional and ion probe u pb analyses of zircons from the otto stock yielded an upper intercept age of 2700 19 ma whereas the more concordant ion probe analyses had a mean 207 pb 206 pb age of 2671 8 ma 2 the latter is interpreted as the age of emplacement of both the volcanics and the pluton and the sm nd mineral isochron age is thought to reflect a period of later disturbance probably during regional metamorphism a high initial e nd of 2 5 1 5 for kirkland lake volcanics indicates long term isotopic depletion of their source this value is the same as that for volcanic rocks throughout the abitibi belt and indicates that any chemically enriched material in the source cannot have been much older than the volcanics themselves an environment remote from older continents is inferred

high resolution u pb ages from the upper triassic chinle formation new mexico usa support a diachronous rise of dinosaurs abstract though the late triassic preserves major paleoenvironmental fluctuations and is key for understanding the evolution of mesozoic and modern terrestrial ecosystems comparisons of late triassic non marine sedimentary and fossil records are difficult because global correlations lack precise radioisotopic ages and have instead been based upon unconstrained biostratigraphic ranges of palynomorph and vertebrate fossils the chinle formation in southwestern north america preserves a major late triassic record of paleoenvironmental and biotic change including significant early dinosaur fossils previous high resolution radioisotopic age constraints for the formation are limited to a single u pb zircon age from the upper third of the formation the extraction of a geologically meaningful age is challenging from these redeposited units and preference is given to considering the youngest age of a deposit as a maximum age and closest approximation of the depositional age because calculating a weighted mean age or median age from a group of ages from such deposits is often not adequate the precision of our two new ca tims single crystal zircon u pb ages from the chinle formation of new mexico is limited to ca 0 3 or 0 7 ma of the youngest crystal age our 206 pb 238 u age of 218 ma from the blue mesa member in six mile canyon western new mexico demonstrates that strata palynomorphs and vertebrate fossils previously considered to be late carnian in age are actually middle norian in age our new age of 212 ma from the hayden quarry within the petrified forest member at ghost ranch northern new mexico provides the first maximum age for important vertebrate assemblages from this area that record the rise of dinosaurs and demonstrates that basal dinosauromorphs dinosaur precursors co existed with dinosaurs for at least 18 ma these new radioisotopic data allow a new correlation of the chinle formation to the late triassic timescale suggesting that most if not all of the lower chinle is norian in age this new correlation has global implications as it allows us to make more precise comparisons with early dinosaur assemblages from the ischigualasto formation of argentina indicating that chinle dinosaur assemblages are significantly younger than those from south america the revised age of the chinle formation also demonstrates that dinosaurs were much rarer in north america at a time when they were abundant in south america supporting hypotheses of paleolatitudinal variation during the rise of dinosaurs

the clementine mission to the moon scientific overview in the course of 71 days in lunar orbit from 19 february to 3 may 1994 the clementine spacecraft acquired just under two million digital images of the moon at visible and infrared wavelengths these data are enabling the global mapping of the rock types of the lunar crust and the first detailed investigation of the geology of the lunar polar regions and the lunar far side in addition laser ranging measurements provided the first view of the global topographic figure of the moon the topography of many ancient impact basins has been measured and a global map of the thickness of the lunar crust has been derived from the topography and gravity

fluxes of fast and epithermal neutrons from lunar prospector evidence for water ice at the lunar poles maps of epithermal and fast neutron fluxes measured by lunar prospector were used to search for deposits enriched in hydrogen at both lunar poles depressions in epithermal fluxes were observed close to permanently shaded areas at both poles the peak depression at the north pole is 4 6 percent below the average epithermal flux intensity at lower latitudes and that at the south pole is 3 0 percent below the low latitude average no measurable depression in fast neutrons is seen at either pole these data are consistent with deposits of hydrogen in the form of water ice that are covered by as much as 40 centimeters of desiccated regolith within permanently shaded craters near both poles

a geographical information system gis study of triassic vertebrate biochronology geographical information systems gis have been applied extensively to analyse spatial data relating to varied environmental issues but have not so far been used to address biostratigraphical or macroevolutionary questions over extended spatial and temporal scales here we use gis techniques to test the stability validity and utility of proposed middle and late triassic land vertebrate faunachrons lvfs a global biostratigraphical framework based upon terrestrial freshwater tetrapod occurrences a database of tetrapod and megafloral localities was constructed for north america and western europe that also incorporated information on relevant palaeoenvironmental variables this database was subjected to various spatial analysis techniques our gis analysis found support at a global level for eocyclotosaurus as an anisian index taxon and probably aetosaurus as a norian indicator other tetrapod taxa are useful biostratigraphical biochronological markers on a regional basis such as longosuchus and doswellia for late carnian time other potential index fossils are hampered however by taxonomic instability mastodonsaurus metoposaurus typothorax paleorhinus pseudopalatus redondasaurus redondasuchus and or are not clearly restricted in temporal distribution paleorhinus angistorhinus stagonolepis metoposaurus and rutiodon this leads to instability in lvf diagnosis we found only in the western northern hemisphere is there some evidence for an anisian ladinian biochronological unit amalgamating the perovkan and berdyankian lvfs and a possible late carnian unit integrating the otischalkian and adamanian megaplants are generally not useful for biostratigraphical correlation in the middle and upper triassic of the study area but there is some evidence for a carnian age floral assemblage that corresponds to the combined otischalkian and adamanian lvfs environmental biases do not appear to strongly affect the spatial distribution of either the tetrapods or megaplants that have been proposed as index taxa in biostratigraphical schemes though several examples of apparent environmental bias were detected by the analysis consequently we argue that further revision and refinement of middle and late triassic lvfs is needed before they can be used to support global or multi regional biostratigraphical correlations caution should therefore be exercised when using the current scheme as a platform for macroevolutionary or palaeoecological hypotheses finally this study demonstrates the potential of gis as a powerful tool for tackling palaeontological questions over extended timescales

assessing relative abundances in fossil assemblages abstract the relative abundances of taxa or skeletal elements in a fossil assemblage can provide important information concerning the palaeoecology and taphonomy of the assemblage however these relative abundances must be estimated from samples of the assemblage rather than measured directly the sampling error this produces decreases the accuracy with which relative abundances can be estimated from the fossil record using the multinomial distribution it is possible to place constraints on the accuracy of estimation of relative abundance provided that two out of three key parameters sample size required degree of similarity and confidence level are known applying this methodology to the fossil record it can be shown that in order to be 95 confident the taxon relative abundances of a fossil assemblage lie within 5 of those found in a sample 534 individuals must be collected this methodology enables the assessment of published relative abundance estimates and the development of sampling protocols for future studies

altered river morphology in south africa related to the permian triassic extinction the permian triassic transition in the karoo basin of south africa was characterized by a rapid and apparently basin wide change from meandering to braided river systems as evidenced by preserved sedimentary facies this radical changeover in river morphology is consistent with geomorphic consequences stemming from a rapid and major die off of rooted plant life in the basin evidence from correlative nonmarine strata elsewhere in the world containing fluvial permian triassic boundary sections suggests that a catastrophic terrestrial die off of vegetation was a global event producing a marked increase in sediment yield as well as contributing to the global 13 c excursion across the permian triassic boundary

the middle permian capitanian mass extinction on land and in the oceans abstract a middle permian mass extinction first discovered in 1994 has become known as the end guadalupian event in the literature however recent studies of foraminifera and brachiopod range truncations in conodont dated sections on the south china block have shown that the losses occur below this level in the middle of the capitanian stage extinctions were suffered by several other groups notably the corals whilst the mollusc record is more enigmatic a major bivalve crisis has been reported in some studies the giant alatoconchids being notable victims but not others gastropods were unaffected by the crisis whilst a roughly contemporaneous ammonoid mass extinction may have occurred in the early wuchiapingian a few million years after the main marine losses compilation of data from plant species in south china reveals a significant 24 loss suggesting that the capitanian crisis also occurred on land an intra capitanian extinction of 56 of plant species in north china block sequences may also have coincided with these losses correlation of these marine and terrestrial extinction events using the palaeomagnetic record provides two alternatives either turnover amongst plant species is contemporaneous with the marine extinction and the eruption of the emeishan flood basalt province in southwest china or plant losses post date the marine extinction and instead coincide with the waning phase of the igneous province current understanding of the major dinocephalian extinction suggests this event occurred during the preceding stage the wordian but future improvements in both sampling and dating this tetrapod crisis may reveal a synchronicity of plant animal and marine invertebrate extinctions the clear temporal link of the capitanian marine extinction with emeishan volcanism suggests that these flood basalt eruptions triggered the crisis a contemporaneous major negative c isotope excursion suggests that like many other mass extinction events methane release from hydrates may also be implicated however in the best dated chinese sections the main excursion is found to slightly post date the extinction which occurs at the end of an unusual and unexplained interval of exceptionally heavy 13c values other usual suspects for mass extinctions either lack geological and palaeontological evidence e g marine anoxia and global cooling or do not precisely correlate with the extinction e g major eustatic regression

marine diversity through the phanerozoic problems and prospects the fossil record provides direct evidence of how diversity has changed over time but cannot be taken at face value diversity curves constructed from counting taxa in the rock record are seriously biased by unevenness of geographical and stratigraphical sampling effort inequality in the rock record available for sampling and inconsistent taxonomic practice sample standardization removes some bias but does not overcome more general incompleteness problems modelling that accounts for potential biases is a newer approach but needs accurate estimates of rock record and consistent taxonomic data uncertainty remains over whether the steep rise in diversity over the last 100 ma is real or reflects sampling bias the repeated rise and fall of marine diversity over time correlates closely with the areal extent of sedimentary deposits and independent estimates of the quality of the fossil record implying a common driving factor namely tectonically mediated sea level change however whether changes in diversity are primarily biological in origin or reflect sampling artefact remains contentious there is a distinct possibility that many of the apparent rises and falls in diversity over the phanerozoic including most of the mass extinctions arise either partially or entirely from rock record bias

on the possibility of clathrate hydrates on the moon one of the most important inferences of the lunar prospector mission data was the existence of subsurface water ice in the permanently shadowed craters near both lunar poles feldman et al 1998 we propose and substantiate an alternative explanation that hydrogen can exist in the shallow lunar subsurface in the form of clathrate hydrates ch4 6h2o and or co2 6h2o the clementine mission in 1994 nozette et al 1994 was the first to suggest the possible existence of subsurface water ice near the poles of the moon the lunar prospector neutron spectrometer data showed near surface deposits enriched in hydrogen near both lunar poles under at least 40 cm of lunar regolith with the assumed density of 2 g cm 3 feldman et al 1998 scientists estimated that as much as 6 billion metric tons of water ice may be buried in these craters under lunar soil in more concentrated deposits than originally thought however the evidence was indirect they cautioned based on reasonable scientific assumptions given the levels of hydrogen detected from which water ice was inferred this conclusion was based on the measurements of the fast and epithermal neutrons by the neutron spectrometer reflected by lunar soil with the source being cosmic rays we propose that the neutron spec trometer data are also consistent with the existence of clathrate hydrates i e g ch4 6h2o and or co2 6h2o in the shallow subsurface of the moon in clathrate hydrates the gas molecule is trapped in a cage by electrical van der waals bonding the controlled crash of nasa s lunar prospector space craft into a crater near the south pole of the moon on july 31 1999 produced no observed signature of water according to scientists analyzing the data from earth based observatories and spacecraft such as the hubble space telescope although the chances of positive detection of water were judged to be 10 worldwide observations of the impact were focused primarily on using sensitive spectrometers tuned to look for the ultraviolet emission lines expected from the hydroxyl oh molecules that should be a by product of any icy rock and dust kicked up by the impact of the spacecraft this lack of physical evidence leaves open the question of whether ancient cometary impacts delivered ice that remains buried in permanently shad owed regions of the moon as suggested by the large amounts of hydrogen measured indirectly from lunar orbit by lunar prospector during its main mapping mission nasa 1999 several possible explanations why any water signature was not detected include the following the spacecraft might have missed the target area the spacecraft might have hit a rock or dry soil at the target site water molecules may have been firmly bound in rocks as a hydrated mineral as opposed to existing as free ice crystals and the impact lacked enough energy to sep arate water from hydrated minerals no water exists in the crater and the hydrogen detected by the lunar prospector spacecraft earlier is simply pure hydrogen studies of the im pact s physical outcome were inadequate the parameters used to model the plume that resulted from the impact were inad equate the telescopes used to observe the impact which have very small fields of view may not have been pointed correctly and water and other materials may not have risen above the crater wall or otherwise were directed away from the tele

timing and magnitude of tetrapod extinctions across the permo triassic boundary a review of the tetrapod amphibian and amniote record across the permo triassic boundary ptb indicates a global evolutionary turnover of tetrapods close to the ptb there is also a within guadalupian tetrapod extinction here called the dinocephalian extinction event probably of global extent the dinocephalian extinction event is a late wordian or early capitanian extinction based on biostratigraphic data and magnetostratigraphy the extinction precedes the illawara reversal so it is not synchronous with the end guadalupian marine extinction the russian ptb section documents two tetrapod extinction events one just before the dinocephalian extinction event and the other at the base of the lystrosaurus assemblage however generic diversity across the latter extinction remains essentially the same despite a total evolutionary turnover of tetrapod genera the chinese and south african sections document the stratigraphic overlap of dicynodon and lystrosaurus in the karoo basin the lowest occurrence of lystrosaurus is in a stratigraphic interval of reversed magnetic polarity which indicates it predates the marine defined ptb so as previously suggested by some workers the lowest occurrence of lystrosaurus cannot be used to identify the ptb in nonmarine strata correlation of the marine ptb section at meishan southern china to the karoo basin based primarily on magnetostratigraphy indicates that the main marine extinction preceded the ptb tetrapod extinction event the ecological severity of the ptb tetrapod extinction event has generally been overstated and the major change in tetrapod assemblages that took place across the ptb was the prolonged and complex replacement of therapsids by archosaurs that began before the end of the permian and was not complete until well into the triassic the tetrapod extinctions are not synchronous with the major marine extinctions at the end of the guadalupian and just before the end of the permian so the idea of catastrophic causes of synchronous ptb extinctions on land and sea should be reconsidered

near surface temperatures on mercury and the moon and the stability of polar ice deposits abstract in order to assess the thermal stability of polar ice deposits we present model calculated temperatures of flat surfaces and surfaces within bowl shaped and flat floored polar impact craters on mercury and the moon our model includes appropriate insolation cycles realistic crater shapes multiple scattering of sunlight and infrared radiation and depth and temperature dependent regolith thermophysical properties unshaded water ice deposits on the surface of either body are rapidly lost to thermal sublimation a subsurface water ice deposit is stable within 2 latitude of the moon s poles meter thick water ice deposits require billions of years to sublime if located in the permanently shaded portions of flat floored craters within 10 latitude of the poles of mercury and 13 latitude of the poles of the moon results for craters associated with radar features on mercury are consistent with the presence of stable water ice deposits if a thin regolith layer thermally insulates deposits at lower latitudes and within smaller craters a regolith cover would also reduce losses from diffusion ion sputtering impact vaporization and h ly and is implied independently by the radar observations permanently shaded areas near the moon s poles are generally colder than those near mercury s poles but the moon s obliquity history its orbit through earth s magnetospheric tail and its radar opaque regolith may limit the volume and radar detectability of ice deposits there

covariation in macrostratigraphic and macroevolutionary patterns in the marine record of north america students of earth history have long recog nized the correlation between the quantity of preserved sedimentary rock and the diversity of life recorded as fossils but paleontologists have yet to determine whether this pattern refl ects a causal relationship or a unidirec tional sampling bias in fossil data imposed by preserved rock quantity distinguishing between these two alternatives has been com plicated by the fact that many of the basic patterns of paleontologic and lithologic co variation have yet to be quantifi ed rigorously here we present the fi rst analyses of the co variation between the macrostratigraphic and macroevolutionary histories of north america based on geographically and tem porally explicit co occurrences of rocks and fossils the analyses use independent quan titative summaries of the stratigraphic and fossil records by integrating the paleobiology database paleodb and macrostrat a mac rostratigraphy database for north america which allows a more direct comparison of the stratigraphic and biological histories of the continent than has heretofore been possible within the macrostrat database the rock re cord is divided into discrete packages of sedi ment that are bound by hiatuses resolvable at the stage level using per interval per pack age rates of sediment package initiation and truncation and genus fi rst and last appear ances herein regional origination and extinc tion we fia substantially stronger positive correlation between sediments and biology for extinction like parameters than we do for origination like parameters four of the largest coincident pulses of regional extinc tion and sediment truncation occur during the widely recognized end ordovician late permian end triassic and end cretaceous mass extinction intervals a further compari son of the global ranges of north american genera to north american macrostratigra phy indicates that the regional and global extinction of genera are more likely to oc cur in the same stage than are global and regional originations together these results suggest that our general understanding of biodiversity dynamics from the fossil record may not be strongly biased by the preserva tion of sediments and leaves open the pos sibility that certain large perturbations to the earth system are responsible for major changes of state in both the sedimentary and biological systems

abrupt and gradual extinction among late permian land vertebrates in the karoo basin south africa the karoo basin of south africa exposes a succession of upper permian to lower triassic terrestrial strata containing abundant terrestrial vertebrate fossils paleomagnetic magnetostratigraphic and carbon isotope data allow sections to be correlated across the basin with this stratigraphy the vertebrate fossil data show a gradual extinction in the upper permian punctuated by an enhanced extinction pulse at the permian triassic boundary interval particularly among the dicynodont therapsids coinciding with negative carbon isotope anomalies

helical burrow casts of therapsid origin from the beaufort group permian of south africa abstract large helical burrow casts of vertebrate origin have been discovered at several localities in the lowermost strata of the teekloof formation of the beaufort group permian in the southwestern karoo basin south africa they are not only the oldest but also the first vertebrate burrows of helical geometry to be found in rocks of pre mammalian age the burrow casts are vertically disposed spiralling tubes filled with fine grained sandstone or siltstone often with a calcareous cement tube diameters gradually increase from 60 mm in the upper entrance decline through two non contacting dextral coils to about 160 mm at the base of the spiral whereupon the tube straightens and widens into a horizontal terminal chamber burrow depths range from 0 5 0 75 m and the ramp angle ranges from 10 to 32 although within any single spiral it is constant articulated skeletons of the small dicynodont diictodon have been found within the terminal chambers and spirals of three sand filled burrows linear ridges preserved on the outer walls and floor of some of the terminal chambers resemble scratch marks possibly made by the claws and beak of diictodon during burrow excavation the sedimentary sequences at two separate localities are interpreted as having been deposited by episodic sheet floods and distributary splay fans in the proximal floodbasin areas flanking an aggrading meanderbelt rise comparison is drawn between helical burrow casts in the lower beaufort and other recorded occurrences in particular daimonelix a beaver burrow from the miocene of nebraska fundamental similarities far outweigh differences to the extent that the beaufort helical burrows may be grouped with the daimonelices it is concluded that the excavation of large helical burrows an activity usually attributed to rodents was pre empted by mammal like reptiles some 50 million years before the first anatomical mammals evolved

non biotic controls of observed diversity in the paleontologic record an example from the permo triassic karoo basin of south africa paleodiversity trends through geologic time can be affected by a number of geologic taphonomic and anthropogenic biases that obscure or prejudice paleoecological patterns in the fossil record although much work has concentrated on the relationship between geologic exposure sample size and taxonomic richness i e number of taxa few studies have investigated the potential effects of dataset quality and changing taxonomy we use four different specimen level datasets of permo triassic tetrapods from the karoo basin of south africa to investigate how sample size geologic outcrop dataset quality and taxonomic revision all affect observed estimates of generic richness evenness and relative abundance our results indicate that large scale patterns of richness evenness and abundance such as the effects of the end permian mass extinction are generally robust to these potential biases across the four different datasets in contrast absolute values vary significantly as do finer scale patterns in agreement with past studies taxonomic errors revised taxonomy and new taxa have little effect on patterns of richness and evenness instead the addition of large numbers of new specimens to the dataset has the largest effect on these paleodiversity metrics despite application of sample standardization we conclude that although large specimen datasets hundreds to thousands of specimens are robust to various potential biases and can recover large scale paleobiologic trends they are still affected by many non biotic controls and workers should strive to improve dataset quality and understand the underlying reasons for observed paleodiversity patterns

vertebrate extinction across permian triassic boundary in karoo basin south africa distinct assemblages of paleosols above and below the permian triassic boundary in the karoo basin of south africa are evidence for reorganization of ecosystems following this greatest of all mass extinctions the permian triassic boundary is recognized from the last appearance of dicynodon and from a series of negative excursions in the isotopic composition of carbon within therapsid tusks pedogenic carbonate nodules and organic matter the boundary is also marked by laminated beds with very weakly developed paleosols a change from purple 10r to brownish red 2 5yr paleosols and a thin 10 cm claystone breccia of reworked soil clasts paleoclimatic changes include a shift from arid and highly seasonal paleoclimate inferred from diffuse and shallow calcareous nodules in permian paleosols to semiarid and less seasonal paleoclimate inferred from deep and well focused calcic horizons in triassic paleosols an earliest triassic shift to warmer and wetter paleoclimate is also indicated by increased chemical weathering abundance of lycopsids and diversity of labyrinthodonts permian paleosols have root traces comparable to those of open shrubland and riparian woodland whereas triassic paleosols have root traces and profile forms like soils of open woodland this is a significant paleoenvironmental change but not as dramatic a change as would be expected from the devastating extinctions of 88 of fossil vertebrate genera latest permian therapsid reptiles were diverse and ecologically specialized in contrast the principal earliest triassic therapsid lystrosaurus was a burrower with no specific habitat preference its short internal nares barrel chest and high neural spines would have given it greater aerobic scope than preexisting therapsids and may have been an advantage under conditions of hypercapnia and hypoxia these adaptations and associated ecosystem changes are compatible with widespread vertebrate mortality by acidosis and pulmonary edema in a post apocalyptic greenhouse created by the voluminous release of methane from shallow marine and permafrost clathrates

methane and carbon dioxide hydrates on mars potential origins distribution detection and implications for future in situ resource utilization 1 there is high probability for the long term crustal accumulation of methane and carbon dioxide on mars these gases can arise from a variety of processes including deep biosphere activity and abiotic mechanisms or like water they could exist as remnants of planetary formation and by products of internal differentiation ch4 and co2 would tend to rise buoyantly toward the planet s surface condensing with water under appropriate conditions of temperature and pressure to form gas hydrate gas hydrates are a class of materials created when gas molecules are trapped within a crystalline lattice of water ice the hydrate stability fields of both ch4 and co2 encompass a portion of the martian crust that extends from within the water ice cryosphere from a depth as shallow as 10 20 m to as great as a kilometer or more below the base of the martian cryosphere the presence and distribution of methane and carbon dioxide hydrates may be of critical importance in understanding the geomorphic evolution of mars and the geophysical identification of water and other volatiles stored in the hydrates of critical importance martian gas hydrates would ensure the availability of key in situ resources for sustaining future robotic and human exploration and the eventual colonization of mars

mapping hydrate stability zones offshore scotland one practical method to reduce environmentally damaging greenhouse gas emissions is through the geological storage of carbon dioxide deep warm storage of carbon dioxide is currently taking place at sleipner north sea and weyburn canada it is however also possible to store carbon dioxide as a liquid and hydrate in cool sub seabed sediments offshore north and west of scotland seafloor pressures and temperatures are suitable for hydrate formation in addition to the possibility of natural methane hydrate being present in this region conditions may also be favourable for carbon dioxide storage as a liquid and hydrate a computer program has been developed to calculate the depth to the base of the carbon dioxide and methane hydrate stability zones in two offshore regions the faeroe shetland channel and the northern rockall trough results predict that methane hydrate remains stable to a maximum depth of 650 m below the seabed in the faeroe shetland channel and 600 m below the seabed in the northern rockall trough the carbon dioxide hydrate stability zone extends below the seabed to a depth of 345 and 280 m respectively no physical evidence for the existence of natural hydrate in these regions has been confirmed suitable conditions for carbon dioxide storage as a liquid and hydrate exist and should this storage method be developed further a more refined program and greater offshore investigations to improve data sets would be necessary to scope the full potential