Taphonomic Influences Research Articles

Putting the cart before the horse: An example of how the lack of taphonomical approaches can mislead paleobiological inferences for the late Ediacaran

The arrival of animals with hard parts at the end of the Ediacaran Period was an important evolutionary innovation. Biomineralized structures serve a number of biological functions and pose environmental challenges. Those same hard parts that once played a role in living organisms also affect their postmortem histories. Taphonomic scenarios may create biases that can impact perceptions on the systematic, morphological, biostratigraphic, and paleogeographic patterns in the fossil record. This is well exemplified by the taxonomic controversies regarding Cloudina, the most geographically widespread and abundant shelly fossil of the uppermost Ediacaran. In this study, we discuss new taphonomic data on Cloudina-bearing strata deposits from the Tamengo Formation (Corumbá Group, Brazil) and how influential this taphonomy is on a robust taxonomy of this fossil. Our observations suggest that allochthonous Cloudina deposits from the Tamengo Formation present evidence of taphonomic influences on the transporting/reworking of fragmentation and disarticulation of Cloudina tubes. Differences in size distributions between some of the localities have demonstrated that this trait is not reliable for defining or synonymizing species of Cloudina, and these differences probably reflect a myriad of taphonomic and paleobiological phenomena. Moreover, in some outcrops of the Tamengo Formation, shell walls are usually poorly preserved due to plastic deformations and diagenetic dissolution/recrystallization processes, which conceal morphological diagnostic features used in Cloudina taxonomy. Similar taphonomic biases may be of equal importance to the taxonomy of Cloudina preserved in other upper Ediacaran carbonates. Hence, earlier claims in favor of the synonymization of Cloudina species from the Tamengo Formation cannot currently be justified.

The botanical provenance and taphonomy of Late Cretaceous Chatham amber, Chatham Islands, New Zealand

Fossil resin (amber) has been recently reported as common, but small, sedimentary components throughout the lower Upper Cretaceous (Cenomanian; 99–94 Ma) strata of the Tupuangi Formation, Chatham Islands, eastern Zealandia. From these deposits, resin has also been identified and obtained from well-preserved, coalified specimens of the conifer fossil Protodammara reimatamorioriMays and Cantrill, 2018. Here, we employed attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) to both dispersed and in situ amber specimens. These resulted in very similar chemical signatures, indicating that these fossils are likely from the same or closely-related botanical sources. The FTIR data are typical of a conifer source within the ‘cupressaceous resins’ category of Tappert et al. (2011). Carbon-13 nuclear magnetic resonance spectroscopy (13C NMR) facilitated the probable identification of these ambers as ‘Class Ib' (sensu Anderson et al. 1992). Based on these spectral data sets, the likely botanical sources of the amber were either Araucariaceae or Cupressaceae; both of these conifer families were common and widespread in the Southern Hemisphere during the Cretaceous. However, the morphology and anatomy of P. reimatamoriori support an affinity to the latter family, thus indicating that the Cretaceous amber of the Chatham Islands was generally produced by members of the Cupressaceae. Comparing the FTIR data to the published spectra of modern resins, we also identify a band ratio which may aid in distinguishing between the FTIR spectra of Araucariaceae and Cupressaceae, and outline the limitations to this approach. A high concentration of ester bonds in Chatham amber specimens, which exceeds typical Cupressaceae resins, is probably caused by taphonomic alteration via thermal maturation. The source of thermal alteration was likely pre-burial wildfires, conditions for which P. reimatamoriori was adapted to as part of its life cycle. A comparison of ambers of the Chatham Islands with modern resins and amber from various localities in Australasia reveals that, taphonomic influences aside, Chatham amber has a unique signature, suggesting that members of the basal Cupressaceae (e.g., Protodammara) were not major contributors to other documented Australasian amber deposits. The closest analogy to Chatham amber deposits appears to be the Upper Cretaceous Raritan Formation, USA, which is characterised by its rich amber, charcoal and Cupressaceae fossil assemblages. This study further supports the hypotheses that the early Late Cretaceous south polar forests were dominated by Cupressaceae, and regularly disturbed by wildfires.

The Issue of Age Estimation in a Modern Skeletal Population: Are Even the More Modern Current Aging Methods Satisfactory for the Elderly?,

The main idea behind age assessment in adults is related to the analysis of the physiological degeneration of particular skeletal structures with age. The main issues with these procedures are due to the fact that they have not been tested on different modern populations and in different taphonomic contexts and that they tend to underestimate the age of older individuals. The purpose of this study was to test the applicability and the reliability of these methods on a contemporary population of skeletal remains of 145 elderly individuals of known sex and age. The results show that, due to taphonomic influences, some skeletal sites showed a lower survival. Therefore, the methods with the highest percentage of applicability were Lovejoy (89.6%) and Rougé-Maillart (81.3%), followed by Suchey-Brooks (59.3%), and those with the lowest percentage of applicability were Beauthier (26.2%) and Iscan (22.7%). In addition, this research has shown how for older adults the study of both acetabulum and auricular surface may be more reliable for aging. This is also in accordance with the fact that auricular surface and the acetabulum are the areas more frequently surviving taphonomic insult.

Reflectance - Current state of research and future directions for archaeological charcoal; Results from a pilot study on Irish Bronze Age cremation charcoals

‘Reflectance’ is a method that estimates the absolute burn temperature of charcoal from the ‘shininess’ of resin mounted samples. The method's usefulness for archaeological charcoal is yet to be comprehensively studied. This article details first results from reflectance testing of archaeological charcoals excavated from Irish Bronze Age cremations, which included calcined bone. As calcination of bone commences at 650 °C, it was expected that the charcoals would reflect at least this temperature. This was not the case for taxonomically identified charcoals >2 mm, nor for micro-charcoals of c. 250 μm, although measured temperatures rose slightly with decreasing fraction size of charcoal remains. Depositional practice, combustion completeness and taphonomic influences may have all played a part in this result, and these will need careful consideration in different archaeological circumstances. However, the greatest challenge for reflectance of archaeological materials lies in obtaining full agreement on the production and use of reflectance calibration curves. Current calibration curves differ substantially, by 100–150 °C ( ±50–75 °C) and in one instance up to as much as 180 °C ( ±90 °C). Without better agreement on calibration, the method's ultimate usefulness in archaeological research will be limited. At the level of refinement currently possible, it will still be useful for determining very high or very low temperature processes, and possibly the difference between charcoal fuel and raw wood fuel fires. The latter has distinct implications for estimating ancient forest wood consumption, since more wood is consumed in processes employing charcoal fuel. Proving the utility of reflectance for archaeological purposes may also require modification of normal practice for archaeological field collection of charcoal, to include collection and laboratory processing of un-sieved soil samples.

Spatial variability of recent macroscopic charcoal deposition in a small montane lake and implications for reconstruction of watershed-scale fire regimes

Sediment and subfossil deposition can vary spatially within a lake because of multiple taphonomic influences. Paleofire reconstructions are commonly based on stratigraphic analysis of macroscopic charcoal in a single core from the central basin of a lake. We investigated the influence of core location on paleofire interpretations. Our approach was to: (1) examine the spatial distribution of recent charcoal deposition in a lake, (2) evaluate the effects of different subsample volumes on charcoal counts, and (3) explore the influence of sediment water content on charcoal concentration values. We retrieved short sediment cores from eight locations, including central, profundal and sublittoral depths, across a small montane lake located in southeastern British Columbia, Canada, to examine the effect of core location on macroscopic charcoal-based reconstructions of fire history. A long sediment core was also collected from the centre of the lake. The pattern of charcoal accumulation in the short cores was compared to the record collected from the lake’s centre, which spans the Holocene. Each short core was stratigraphically matched with the long core using a discrete tephra marker to form a continuous record and examine the influence of core location on the interpretation of long-term fire regimes. We also examined how sample volume (1 vs. 5 cm3) from a single core affected macroscopic charcoal analysis and paleofire interpretation. Finally, we compared paleofire reconstructions generated from charcoal accumulation rates from wet sediment volume (CHAR) and dry sediment weight. Results were generally similar, but differed slightly in uppermost unconsolidated sediments. Even in small lakes with simple bathymetry, bulk sedimentation rates and charcoal accumulation rates may vary throughout the basin. The best record of past fires is preserved in sediment cores from the flattest and deepest area of the basin. These findings suggest that lake-bottom topography is an important consideration when targeting coring locations and interpreting charcoal data. Understanding how coring location, core sampling strategies and data processing affect paleofire inferences is important for generating robust quantitative paleoecological interpretations.

“Funerary bundles” in the PPNB at the archaeological site of Tell Halula (middle Euphrates valley, Syria): analysis of the taphonomic dynamics of seated bodies

This paper presents the results of the taphonomic analysis of the burials from Tell Halula (Middle Euphrates Valley, Syria). The numerous burials recovered from this Pre-Pottery Neolithic B (PPNB) settlement, in addition to the large volume of field documentation, have provided an opportunity to study burials in more depth than is usually allowed. This data set is important because of the unique mode of deposition, the exceptional preservation of the related assemblages (including fabrics, mats, and basketry) and the highly standardized nature of the funerary practices. Although the burials were found in various stages of preservation and articulation, we will show that they all represented the same type of funerary deposit, namely seated burials, often encased in bottle-shaped funerary bundles, and that the variability found during excavation can be attributed to post-depositional taphonomic effects. We provide a study of the different forms that result from these taphonomic influences and highlight the importance of doing this type of analysis. We hope that this paper will be a valuable contribution to the growing body of literature surrounding both seated burials and the taphonomy of burials.

Classification of Sex and Ancestry from Metatarsal Bones by Radiographic Analysis

It is difficult to accurately estimate sex and ancestry from incomplete skeletal remains; particularly when the skull and pelvis are absent. It is necessary to be able to accurately estimate a biological profile from multiple bones because skeletal remains are often found incomplete. Metatarsal bones are ideal candidates for estimation of sex and ancestry because they are more numerous than other post‐cranial bones and are usually found intact enclosed in shoes, protected from taphonomic influences. The goal of this study was to evaluate the presence of sexual and ancestral differences in metatarsal bones from a modern population. To evaluate these differences, we analyzed radiographs taken between 2003 and 2012, recording length and width measurements of metatarsal bones. We then performed discriminant function analysis to determine which measurements were most useful to classify sex and ancestry. We found that we could correctly classify sex and ancestry independently, 78.4% and 59.3% of the time, respectively; additionally 45.9% of individuals were correctly classified when sex and ancestry were pooled. In conclusion, our data suggests that there are sexual and ancestral differences present in metatarsal bones. Furthermore, our results suggest that a whole set of metatarsals is preferred to estimate sex and ancestry, with an emphasis placed on the first metatarsal bone.Grant Funding Source: LECOM Internal Grant

Chapter 25 Palaeogeographical distribution of Ordovician Radiolarian occurrences: patterns, significance and limitations

Abstract Over the past 15 years, significant progress has been achieved in our understanding of Lower Palaeozoic radiolarian faunas. However, description of biogeographical patterns of Ordovician Radiolaria is hampered by the paucity of known occurrences as well as possible taphonomic influences. The distribution of all known assemblages is analysed in time and space. Lower Ordovician (especially Tremadocian) Radiolaria are known from two distinct tropical localities of Laurentia. Geographical coverage is much better for the Middle Ordovician (Darriwilian). However, data are concentrated in tropical palaeolatitudes (between 30°N and 30°S). The absence of data from mid/high-latitude localities limits any biogeographical insights. In addition to this there are taphonomic and taxonomic biases. Data are also sparse for the Upper Ordovician. However, comparison between Australian and Nevadan material of Katian age shows strong similarities, suggesting the presence of a coherent tropical radiolarian bioprovince, as in the modern ocean.

Τesting models for the beginnings of the Aurignacian and the advent of figurative art and music: The radiocarbon chronology of Geißenklösterle

The German site of Geißenklösterle is crucial to debates concerning the European Middle to Upper Palaeolithic transition and the origins of the Aurignacian in Europe. Previous dates from the site are central to an important hypothesis, the Kulturpumpe model, which posits that the Swabian Jura was an area where crucial behavioural developments took place and then spread to other parts of Europe. The previous chronology (critical to the model), is based mainly on radiocarbon dating, but remains poorly constrained due to the dating resolution and the variability of dates. The cause of these problems is disputed, but two principal explanations have been proposed: a) larger than expected variations in the production of atmospheric radiocarbon, and b) taphonomic influences in the site mixing the bones that were dated into different parts of the site. We reinvestigate the chronology using a new series of radiocarbon determinations obtained from the Mousterian, Aurignacian and Gravettian levels. The results strongly imply that the previous dates were affected by insufficient decontamination of the bone collagen prior to dating. Using an ultrafiltration protocol the chronometric picture becomes much clearer. Comparison of the results against other recently dated sites in other parts of Europe suggests the Early Aurignacian levels are earlier than other sites in the south of France and Italy, but not as early as recently dated sites which suggest a pre-Aurignacian dispersal of modern humans to Italy by ∼45000 cal BP. They are consistent with the importance of the Danube Corridor as a key route for the movement of people and ideas. The new dates fail to refute the Kulturpumpe model and suggest that Swabian Jura is a region that contributed significantly to the evolution of symbolic behaviour as indicated by early evidence for figurative art, music and mythical imagery.

Radiocarbon dating & Bayesian modelling from the Grotte du Renne & a Neanderthal origin for the Châtelperronian

Hublin et al (2012) have published a new series of AMS determinations from the site of the Grotte du Renne at Arcy-sur-Cure, one of the key sites in discussions regarding late Neanderthal behavior and adaptation. The site is well known as one of the very few Châtelperronian sites that appear to contain evidence for the range of ornaments and objects that are usually found in sites of the Proto- or Early Aurignacian in Europe, and therefore associated with anatomically modern humans. For this reason it is important that we have an idea of the chronology of the sequence here, so that we may compare it with other contexts where similar cultural horizons have been excavated.Higham et al (2010) published a series of 31 AMS dates from well-selected humanly-modified material from several layers of the site. They found variation in the results that they ascribed to taphonomic influences, which implied strongly that there was some degree of mixing of material within the site. They recommended that caution was ther...

Why do foliar physiognomic climate estimates sometimes differ from those observed? Insights from taphonomic information loss and a CLAMP case study from the Ganges Delta

Palaeoclimate estimates derived from plant-based proxies are potentially subject to uncertainties arising from taphonomic filtering. In any given fossil assemblage it is possible to identify the kinds of likely taphonomic influences, but virtually impossible to quantify the uncertainties they introduce because filtering removes information. Because that information is missing it cannot be measured. An alternative approach is to measure the maximum uncertainty possible due to specific information loss within recognised analytical protocols. In respect of the multivariate foliar physiognomic technique known as CLAMP (Climate Leaf Analysis Multivariate Program) we have attempted to do this by experimentally degrading both the character state scores and the number and composition of taxa as subsets of the full range of character states and taxonomic diversity in the source vegetation. In this study a stand of protected vegetation on Green Island (23° 08′ 58″ N, 88° 26′ 59.19″ E) within the Ganges Delta was sampled following standard CLAMP protocols. The island is subject to annual flooding during the monsoon season and is typical of the kinds of naturally disturbed vegetation likely to be represented in ancient delta floodplain assemblages. A total of 56 woody dicot taxa were scored in the living vegetation. From this ‘complete’ sample leaf character states for lobing, margin, size, apex, base, length-to-width ratio and shape were removed in turn from all 56 taxa to give 7 analyses simulating worst case taphonomic loss of physiognomic data. Ten subsets of 20 randomly selected taxa were also analysed to simulate taphonomic diversity loss of almost two thirds of the potentially available taxa in the source vegetation. In all cases the completeness statistic remained above the CLAMP recommended minimum of 0.66. The results show that in all cases the uncertainties arising from taphonomic processes, either through taphonomic diversity or character state filtering, were not significantly different from the statistical CLAMP uncertainties associated with the most commonly used calibration dataset (Physg3brc), and gave similar climatic estimates as the source vegetation in its entirety. This suggests that stratigraphically well constrained museum collections lacking detailed sedimentary or taphonomic context can still be used with confidence for CLAMP analyses. Leaf margin analysis displayed a greater sensitivity to diversity loss. The Green Island estimates suggested a cooler, moister climate than that indicated by the observed regional climate as derived from a 0.5 × 0.5° gridded data set used in climate modelling evaluation. The likely cause for this disparity is the prevalence of a sub-canopy microclimate signal developed by the vegetation itself, and this is strongly dependant on the temperature and humidity characteristics of the regional climate as well as the proximity to water bodies. Within the sample size limitations of this study this disparity is larger than that introduced by taphonomic processes, but potentially can be corrected for.

Unusually preservedMetaconularia manni(Roy, 1935) from the Silurian of Iowa, and the systematics of the genus

The Welton Member of the Scotch Grove Formation at Shaffton Quarry, near Camanche, Iowa, is about 427 Ma old and contains numerous metaconulariid specimens, many of which are preserved in apex-downward orientation. Some of these show an unusual, splayed, “Maltese cross” configuration. Apex-downward configurations suggest rapid burial, consistent with the soft part preservation known in other taxa from this locality. The abundance ofMetaconulariaat Shaffton Quarry, and of topotype specimens ofM. aspersa, the generic type species, permits evaluation of the degree of individual and intracollectional variation in peridermal ornament. Variation within and among individuals precludes reliance on ornamental differences in species differentiation in most cases. In view of these results we assign all Shaffton specimens toMetaconularia manni(Roy, 1935), and reviseMetaconulariabased on its type material from Europe and other material from Europe and North America. An exploratory phylogenetic analysis highlights aspects of character distribution within the genus, but the small number of characters states and possible taphonomic influences upon them limit confidence in the clade topology. Subgroups within the genus are characterized by larger, discoidal papillae, and by strong transverse corrugation and sinuous rows of smaller papillae. The genus itself comprises those conulariids with an external ornamentation of simple, round, small papillae, paired internal septae along the midlines, and a thin periderm that was to some degree pliable during life.

Technical note: Applicability of tooth cementum annulation to an archaeological population

The use of tooth cementum annulations for age determination has been deemed promising, exhibiting high correlations with chronological age. Despite its apparent potential, to date, the tooth cementum annulations method has been used rarely for estimating ages in archaeological populations. Here we examine the readability of cementum annulations and the consistency of age estimates using a sample of 116 adults from the Iron Gates Gorge Mesolithic/Neolithic series. Our examination of the method pointed to several sources of error that call into question the use of this method for estimating the chronological ages of archaeologically derived dental samples. The poor performance of the method in our analysis might be explained by taphonomic influences, including the effect of chemical and biological agents on dental microstructures.

DNA Preservation in Skeletal Elements from the World Trade Center Disaster: Recommendations for Mass Fatality Management*,†

The World Trade Center (WTC) victim identification effort highlights taphonomic influences on the degradation of DNA from victims of mass fatality incidents. This study uses a subset of the WTC-Human Remains Database to evaluate differential preservation of DNA by skeletal element. Recovery location, sex, and victim type (civilian, firefighter, or plane passenger) do not appear to influence DNA preservation. Results indicate that more intact elements, as well as elements encased in soft tissue, produced slightly higher identification rates than more fragmented remains. DNA identification rates by element type conform to previous findings, with higher rates generally found in denser, weight-bearing bones. However, smaller bones including patellae, metatarsals, and foot phalanges yielded rates comparable to both femora and tibiae. These elements can be easily sampled with a disposable scalpel, and thus reduce potential DNA contamination. These findings have implications for DNA sampling guidelines in future mass fatality incidents.

Early Cambrian metazoan fossil record of South China: Generic diversity and radiation patterns

South China with its rich fossil record is an important region for studying Early Cambrian metazoan diversity patterns. Compilation of a database of metazoan genera from the traditional Lower Cambrian (Cambrian Series 1–2) of South China allows a quantitative analysis of biodiversity changes. The dataset shows that about 876 genus names have been reported from the Lower Cambrian of South China. Of these only about 582 genera are now considered valid after taxonomic scrutiny. Plotting generic diversity shows a two-part, first-order trend: 1, diversity increase through the most of the Meishucunian and Qiongzhusian stages (South China usage), but punctuated by a modest decline during the upper Meishucunian; followed by 2, diversity decline in the Canglangpuan and Longwangmiaoan stages (South China usage). About 155 genera of small shelly fossils (SSFs) occur in Meishucunian rocks. The Meishucunian fauna is dominated by helcionellids, orthothecimorph hyoliths and other enigmatic fossils and is very consistent with the pretrilobitic ‘Tommotian Fauna’. Diversity increases in the Qiongzhusian stage, reaching 304 genera, the peak value known for the Cambrian. The Qiongzhusian fauna is characterized mainly by the occurrence of dominant pan-arthropods and crown-group brachiopods, representing an initial phase of the Cambrian Evolutionary Fauna. A substantial decline in generic diversity through the Canglangpuan (ca 153 genera) and Longwangmiaoan (ca 69 genera) stages is due partly to a eustatic regression, and it approximates the global pattern, reflecting an extinction event at the end of the Lower Cambrian. The observed regional biodiversity through this interval has both evolutionary and taphonomic influences: the decline in SSF diversity beginning in the upper Meishucunian was not only related to the decimation of SSFs, but also to a reduction in phosphogenesis. An apparent peak in diversity during the Qiongzhusian was somewhat exaggerated by the exceptional Chengjiang Biota.

New Silurian cooksonias from dolostones of north-eastern North America

New specimens of Cooksonia and Hostinella are described from the Bertie Group of Ontario and New York State, which is dated by faunas as latest Silurian (Přídolí). The rare plant fossils are unusual in that they are preserved in fine-grained, slightly argillaceous dolostones (‘waterlime’) rather than clastic rocks. At least two species of Cooksonia are present, one with ± globular sporangial morphology close to C. hemisphaerica Lang. Those with ellipsoidal/discoidal sporangia are compared with C. pertoni Lang, C. paranensis Gerrienne et al. and C. bohemica Schweitzer, the latter represented by a single specimen from the Přídolí of the Czech Republic. However, the paucity of specimens, which prevents assessment of taphonomic influences on shape, combined with the absence of any anatomical features and the gross morphological simplicity of the fossils, precludes specific assignment. Specimens of Hostinella include one in which apices and a lateral basal structure resembling a root are preserved. It is concluded that the Laurentian assemblage of Ontario and New York State is less diverse and disparate than coeval assemblages, which are also preserved in marine rocks. Its preservation in limestones may have been facilitated by the hypersalinity inferred from various sedimentary features, which would restrict the activity of many decomposers.

Taphonomic influences on the interpretation of the palaeoecological record from Lynch’s Crater, northeastern Australia

Abstract Pollen and plant macrofossil analysis of a sediment core from the margin of Lynch’s Crater provides a discontinuous record of vegetation and environments on and around Lynch’s Crater through the last glacial cycle. A chronology for the sequence is provided by palynological correlation with an existing, more continuous record from the central part of the crater. A comparison of the two records provides insights into processes of pollen transport and deposition that allows clearer separation of regional vegetation from that growing on the swamp surface. There is evidence from both pollen and macrofossils for the existence of a previously unsuspected swamp forest which grew on the swamp margins within the early part of the last glacial. The records illustrate the extinction of components of this forest in the latter part of the last glacial period and its eventual demise in the Holocene.

Ecology and taphonomy of Dominican Republic amber and its inclusions

The taphonomic influences upon fossil faunas are generally assumed to be substantial, but in amber they have been little investigated. By comparing the inclusions in Tertiary amber from the Dominican Republic (Smithsonian Institution's Brodzinsky-Lopez Pena collection) with modern insect populations sampled using various methods and from different habitats, it is possible to test taphonomic hypotheses that bear on interpretations of amber faunas. The biota trapped in amber is here viewed as analogous to modem faunas sampled with man-made traps. Using cluster analysis (Manhattan and Euclidian distance measures -UPGMA clustering algorithm) to compare faunas, the amber-trap fauna is most closely reproduced by present day collection using emergence traps and also shows a strong similarity to the fauna of pitfall trap samples. Faunal dissimilarities indicate that the utility of Dominican Republic amber fossils is limited for ecological studies of the canopy and shrub layers of forests, or of the Orders Coleoptera, Diptera or Hymenoptera. Similarities between modern faunas and the amber fauna allow predictions about the ecological setting of Tertiary amber production: this is indicated as primary rain forest, with regenerating patches of secondary growth, in a low-altitude riparian location. □Amber, Dominican Republic, Palaeogene, ecology, taphonomy.

Taphonomic constraints on foliar physiognomie interpretations of Late Cretaceous and tertiary palaeoeclimates

Foliar physiognomic interpretations of Late Cretaceous and Tertiary palaeoclimates, such as those derived from Leaf Margin Analysis, usually rely on taxon-based observations from the forest canopy. In these analyses, Southern Hemisphere rainforests are sometimes considered analogues of North American Late Cretaceous vegetation. Past analyses have not considered taphonomic biases. Taphonomic influences on specimen-based and taxon-based approaches to foliar physiognomic analyses of palaeoclimate are assessed here using forest-floor and stream-bed leaf litter from modern Australian rainforests.Forest floor leaf litter is markedly local in origin and is taxonomically biased towards leaves from canopy trees. Litter has smaller leaves than expected from the canopy, using either specimen- or taxon-based observations. The Leaf Size Index (LSI) is moderately robust to taphonomic bias, with a correction factor of 3:2 for canopy LSI: forest-floor LSI. Leaf margin type is highly variable using specimens or when total species numbers are low. The accuracy of palaeotemperature interpretations based on leaf margin type alone (Leaf Margin Analysis) are therefore strongly affected by taphonomic biases and local floristics. Direct comparisons between canopy and fossil leaf assemblages may therefore misrepresent the palaeoclimate of the oriinal standing vegetation. Fluvially transported assemblages may exaggerate this bias. However, a “foliar physiognomic signature” is defined for these modern leaf beds using leaf-size, shape and margin type from specimen-, rather than taxon-based observations. Multivariate analysis (Discriminant Analysis) of the foliar physiognomic signature of these leaf beds can differentiate between leaf beds from each of the forest-types examined. Examination of modern leaf assemblages allow an a priori analysis of taphonomic influences on foliar physiognomic character, in contrast to ad hoc hypotheses used in comparisons based on canopy observations, and potentially offer more reliable reconstructions of Late Cretaceous and Tertiary palaeoclimates from leaf megafloras than have previously been shown.

Constraints on Siluran and Early Devonian phytogeographic analysis based on megafossils

Abstract The detection of phytogeographic patterns in Silurian and Early Devonian land vegetation is hampered by the dearth of occurrences of megafossils, the absence of consistently precise correlation, unreliability of identification, and the lack of sufficient detailed sampling and information on sediments to permit evaluation of taphonomic influences on composition of assemblages. Interpretation is further complicated by the exceptional evolutionary position of the plants themselves and the lack of extant representatives. There is little information on whole plants, their life histories, their ecological and climatic tolerances. The composition of Ludlow, Pridoli and Lochkovian/Gedinnian assemblages is analysed. Those from Kazakhstan and Siberia are particularly enigmatic. The assemblages are plotted on the appropriate continental reconstructions. Most are clustered on the southeast margin of Laurussia and very few occur at high latitudes. In Ludlow time, Baragwanathia dominated assemblages in Australia in contrast with the rhyniophytoid assemblages of Laurussia. New information from Kazakhstan and northwest China adds to the data base in the Pridoli. Differences in Gedinnian assemblages from South Wales, the Welsh Borderland and Scotland, where sediments have been intensively studied and correlation is based on fish faunas and, more usefully, on palynomorphs, are related to taphonomy, to local vegetation distribution pattern, and to evolutionary changes. World-wide analysis of occurrences shows four distinct assemblages, based on Laurussia, Kazakhstan, Australia and Siberia, the latter being a rare example of high latitude vegetation.