Comparing amber fossil assemblages across the Cenozoic

To justify faunistic comparisons of ambers that differ botanically, geographically and by age, we need to determine that resins sampled uniformly. Our pluralistic approach, analysing size distributions of 671 fossilized spider species from different behavioural guilds, demonstrates that ecological information about the communities of two well-studied ambers is retained. Several lines of evidence show that greater structural complexity of Baltic compared to Dominican amber trees explains the presence of larger web-spinners. No size differences occur in active hunters. Consequently, we demonstrate for the first time that resins were trapping organisms uniformly and that comparisons of amber palaeoecosystem structure across deep time are possible.     

The relationship between fossil diatom assemblages and limnological conditions

Fossil diatom assemblages from the sediment/water interface in 105 Minnesota lakes were compared with measurements of alkalinity, sulphate, total phosphorus, transparency, and water depth at the sample site. Similar assemblages were placed together using cluster analysis and comparisons of environmental variables between diatom clusters were made using an analysis of variance. Total alkalinity and transparency showed the greatest difference among clusters. Samples from shallow eutrophic prairie lakes were dominated by Melosira granulata, Stephanodiscus niagarae and, occasionally, by Stephanodiscus hantzschii. Deep oligotrophic lakes had modest percentages of Cyclotella comta. Dilute acid lakes were dominated either by Melosira distans and M. italica or by Tabellaria fenestrata, Cyclotella stelligera, and in some cases C. glomerata. Assemblages with Cyclotella glomerata and Synedra nana were found in naturally meromictic lakes. Stephanodiscus hantzschii showed a preference for extremely eutrophic lakes. The relationships between recently deposited diatom assemblages and the lake environmental conditions studied here can be used to evaluate the extent of past environmental change in lakes.     

A method for reconstructing climate from fossil beetle assemblages

Fossil beetle remains have been used to reconstruct temperatures. One method by which these reconstructions are made--the Mutual Climatic Range method--is based on the overlap of the observed modern climatic ranges of the beetles present in a fossil sample. A limitation of this method is that it does not exploit variations in the rate of occurrence of a species within its climatic range. We present an alternative method that uses observed variations in this rate in modern data for climate reconstruction. The method is shown to perform well in an experiment using modern data from North America.     

Influence of transportation and time-averaging in fossil assemblages from the Pennsylvanian of Oklahoma

The relative effects of shell destruction, transportation, and time-averaging have been assessed in seventeen soft-bottom, benthic fossil collections from the Pennsylvanian Wewoka Formation in Hughes County, Oklahoma. Invertebrates were identified to species level, and each was subject to a taphonomic evaluation to determine whether it was in place. Species that were not deemed parautochthonous (living at the location of collection shortly before final burial) were eliminated from the faunal lists to reduce the effects of time-averaging and transportation in the fossil assemblages. Both reciprocal averaging and non-metric multidimensional scaling ordinations revealed two biofacies. These were distinguished using both presence/absence data and numerical counts of species despite an overwhelming number of taxa occurring in both biofacies. Comparison between ordinations based on entire faunal lists with those based on parautochthonous faunal lists indicates that the two biofacies faithfully reproduce differences in the living distributions of member taxa but that the two biofacies underwent different degrees of time-averaging and transportation. Time-averaging leads to accumulation of taxa over time, thereby making presence/absence composition of collections more similar. Transportation, on the other hand, homogenizes originally patchy population distributions and makes relative abundances more uniform. Based on differences in abundances and presence/absence patterns, the stratigraphically lower biofacies underwent more transportation and more time-averaging than the upper biofacies.     

Comparison of contemporary and fossil diatom assemblages from the western Antarctic Peninsula shelf

During the past ten years, the Antarctic Peninsula has been identified as the most rapidly warming region of the Southern Hemisphere and it is important to place this warming in the context of the natural climate and oceanographic variability of the recent geological past. Many biological proxies, such as marine diatom assemblages, have been used to determine Southern Ocean palaeoceanographic conditions during the Late Quaternary, however, few investigations have attempted to link observations of modern floras with the fossil record. In this study we examine a suite of modern austral spring (December 2003) and summer (February 2002) surface water samples from along the western Antarctic Peninsula (WAP) continental shelf and compare these to core-top, surface sediment samples. Using detrended correspondence analysis (DCA) and principal component analysis (PCA) of diatom abundance data we investigate the relationship of contemporary diatom floras with the fossil record. This multivariate analysis reveals that our modern assemblages can be divided into three groups: summer southern WAP sites, summer northern WAP sites, and spring WAP sites. Sea surface temperature (SST) is an important environmental variable for explaining seasonal differences in diatom assemblages between spring and summer, but sea surface salinity (SSS) is more important for understanding temporally-equivalent regional variations in assemblage. Our summer diatom samples are more reminiscent of early season assemblages, reflecting the unusually late sea ice retreat from the region that year. When the modern assemblages are compared to the fossil record, it is clear that most of the important diatoms from the summer assemblage are not preserved into the sediments, and that the fossil record more closely reflects spring assemblages. This observation is important for any future attempts to quantitatively reconstruct palaeoceanographic conditions along the WAP during the Late Quaternary and highlights the need for many more such studies in order to address longer timescales, such as interannual variability, in the context of the fossil record.     

BioDeepTime: A database of biodiversity time series for modern and fossil assemblages

Motivation

We have little understanding of how communities respond to varying magnitudes and rates of environmental perturbations across temporal scales. BioDeepTime harmonizes assemblage time series of presence and abundance data to help facilitate investigations of community dynamics across timescales and the response of communities to natural and anthropogenic stressors. BioDeepTime includes time series of terrestrial and aquatic assemblages of varying spatial and temporal grain and extent from the present-day to millions of years ago.

Main Types of Variables Included

BioDeepTime currently contains 7,437,847 taxon records from 10,062 assemblage time series, each with a minimum of 10 time steps. Age constraints, sampling method, environment and taxonomic scope are provided for each time series.

Spatial Location and Grain

The database includes 8752 unique sampling locations from freshwater, marine and terrestrial ecosystems. Spatial grain represented by individual samples varies from quadrats on the order of several cm² to grid cells of ~100 km².

Time Period and Grain

BioDeepTime in aggregate currently spans the last 451 million years, with the 10,062 modern and fossil assemblage time series ranging in extent from years to millions of years. The median extent of modern time series is 18.7 years and for fossil series is 54,872 years. Temporal grain, the time encompassed by individual samples, ranges from days to tens of thousands of years.

Major Taxa and Level of Measurement

The database contains information on 28,777 unique taxa with 4,769,789 records at the species level and another 271,218 records known to the genus level, including time series of benthic and planktonic foraminifera, coccolithophores, diatoms, ostracods, plants (pollen), radiolarians and other invertebrates and vertebrates. There are to date 7012 modern and 3050 fossil time series in BioDeepTime.

Software Format

SQLite, Comma-separated values.     

Application of trophic transfer efficiency and age structure in the trophic analysis of fossil assemblages

We evaluate onshore-offshore trends in age-frequency distributions and trophic transfer efficiencies using 11 modern death assemblages off the Texas coast. Trophic transfer efficiencies within trophic levels offer little insight over that achieved by a size-frequency distribution. Production/biomass ratios will always be 1 in the fossil record. Within trophic-level estimates of paleogrowth efficiency, the ratio of paleoproduction to paleoingestion (Pⁱ_glt/Iⁱ_lt where i indicates the i^th trophic level and lt indicates the time-averaged value) follow the expected ecological trend precisely in that paleogrowth efficiency is consistently higher in primary consumers than in predators in all 11 death assemblages. Paleoutilization efficiency, the ratio of predator paleoingestion to prey paleoproduction, I²_lt^°/P¹_glt^°, may provide information on the degree of bias in the preservation of primary (1 °) and secondary (2 °) consumer trophic groups. I²_lt^°/P¹_glt^° fell below 0.1 in most cold-seep and bay assemblages, indicating a large surplus of primary consumers. In sharp contrast, I²_lt^°/P¹_glt^°     

Application of the Wagner's Parsimony Method in fossil plant assemblages from the Cretaceous of Europe

Wagner's Parsimony Method, a grouping method used in phylogeny and synecology, is applied for the first time to taxon lists of fossil plant assemblages from the Albian–Cenomanian of Europe. When compared to a “classical” Correspondence Analysis, WPM allows for a higher resolution, using taxa named in “cf.” or “aff.” and points out both clusters and gradients. WPM results in a tree in which localities order according to their species content and minimizes the number of changes of character states (presence/absence), whereas Correspondence Analysis plots the localities along axes and maximizes the inertia (“variance” explaining most differences between localities). Close relationships exist between the plant palaeobiocenoses and palaeobiotopes, the latter being inferred from taphonomical data (especially the salinity and the clastic size). The space/time working scale can be very fine, up to the landscape ecology level.     

A novel approach for predicting the probability of ignition of palaeofires using fossil leaf assemblages

Many metrics are used to predict and manage wildfires today but it is difficult to directly apply these to past wildfires histories. Developing an approach that enables estimation of these fire metrics in the past would provide significant power in our ability to compare past fire risk with that of the modern day. We use the Climate Leaf Analysis Multivariate Program (CLAMP) to estimate warm month mean temperature and annual mean relative humidity for a modern day leaf dataset and establish a novel methodology by which we can generate ‘pseudo‐daily’ meteorological parameters to calculate the probability of ignition (p(I)), an aspect of the North American Fire Danger Rating System. We test this methodology on Tortonian aged fossil leaves (11.62–7.25 Ma) from five sites across California, which reveal that the Tortonian was cooler and considerably more humid and that p(I) was lower during this time than in the region today.     

Gradient versus cluster analysis of fossil assemblages: a comparison from the Ordovician of southwestern Virginia

Studies in modern ecology indicate that most species are distributed independently along environmental gradients according to their individual requirements. Steep gradients often produce species associations separated by discontinuities; gradual gradients produce broadly-overlapping distributions. Approaching the distribution of species populations as a continuum, using gradient analysis, avoids artificial subdivision of totally intergrading distributions, yet permits discontinuities to emerge where present. Faunas of the Martinsburg Formation (Ordovician) in southwestern Virginia offer an excellent opportunity to test the applicability of gradient analysis in a paleoecological setting. A broad spectrum of environments, from nearshore to open-marine, clastic to carbonate-dominated facies, provide both temporal and geographic variation against which to evaluate changes in species distributions. Variations of five classical, Petersen-type communities were recognized in the Martinsburg using cluster analysis: (1) Lingula, (2) bivalve, (3) Rafinesquina, (4) Onniella, and (5) Sowerbyella-dominated communities. Two gradient analysis techniques, ordination and Markov analysis, revealed the same basic associations. However, ordination and Markov analysis permit arrangement of these associations along one or more interpreted environmental gradients. Factors related to water depth and distance from clastic source areas, particularly bottom stability and disturbance frequency, appear to have been the most important of a complex of interrelated physical parameters. The high-stress, nearshore end of the Martinsburg gradient complex was occupied by a Lingula association, followed seaward by an association of bivalves adapted to less-stressed environments. Low-stress, open-shelf environments were occupied by Rafines-quina, Onniella, or Sowerbyella-dominated associations. Broad overlaps among these articulate brachio-pod associations reflect variations in the open-shelf habitat.     

Topography and tectonics of the Taconic outer trench slope as revealed through gradient analysis of fossil assemblages

Similarities in stratigraphic sequence, syndepositional topography and tectonics, and regional tectonic setting between the Mohawk Valley, New York, in the Middle Ordovician and the Australian flank of the Timor Trough today support the idea that the Taconic Foreland Basin orginated in an arc-continent collision. The Trenton Group strata studied - a roughly four million year long sequence correlated by bentonite beds along an 83 km downslope transect in the central Mohawk Valley - represent the continental shelf and outer trench slope. Bank limestones pass upward and downslope into deep water black shales in a manner reminiscent of the lateral and vertical sedimentary sequence on the Sahul Shelf and Australian flank of the Timor Trough. In studying topography, relative depth was measured through reciprocal averaging ordination of benthic macroinvertebrate fossil assemblages. Downslope bathymetric profiles show the development of a horst and graben topography coincident with regional tilting and transgression - a pattern associated with downward flexure of the Australian Plate approaching Timor. The net rate of transgression corresponds to an arc-continent convergence rate on the order of 2 cm per year.     

Taphonomy and compositional fidelity of Quaternary fossil assemblages of terrestrial gastropods from carbonate-rich environments of the Canary Islands

Quaternary aeolian deposits of the Canary Islands contain well‐preserved terrestrial gastropods, providing a suitable setting for assessing the taphonomy and compositional fidelity of their fossil record over ~13 kyr. Nine beds (12, 513 shells) have been analysed in terms of multivariate taphonomic and palaeoecological variables, taxonomic composition, and the stratigraphic and palaeontological context. Shells are affected by carbonate coatings, colour loss and fragmentation. Shell preservation is size‐specific: juveniles are less fragmented and show colour preservation more commonly than adults. In palaeosols, the adult shell density correlates negatively with the proportion of fragmented adults, negatively with the proportion of juveniles, and positively with the proportion of adults with coatings. High bioturbation intensity in palaeosols is associated with low shell fragmentation and high proportion of shells with coatings. These relationships imply that high adult density in palaeosols was driven by an increase in shell production rate (related to a decrease in predation rates on adults and a decrease in juvenile mortality) and a decrease in shell destruction rate (related to an increase in durability enhanced by carbonate precipitation). In dunes, the relationships between taphonomic alteration, shell density and bioturbation are insignificant. However, dune assemblages are characterized by a lower frequency of shells with coatings and higher rates of colour loss, indicating lower shell durability in dunes than in palaeosols. Additionally, non‐random differences in the coating proportion among palaeosols imply substantial temporal variation in the rate of carbonate crust formation, reflecting long‐term changes in bioturbation intensity that covaries positively with shell preservation. Dunes and palaeosols do not differ in species abundances despite differences in the degree of shell alteration, suggesting that both weakly and strongly altered assemblages offer data with a high compositional fidelity. Carbonate‐rich terrestrial deposits originating in arid conditions can enhance the preservation of gastropods and result in fossil assemblages that are suitable for palaeoecological and palaeoenvironmental studies of terrestrial ecosystems.     

Intrinsic qualities of primate bones as predictors of skeletal element representation in modern and fossil carnivore feeding assemblages

Plio-Pleistocene faunal assemblages from Swartkrans Cave (South Africa) preserve large numbers of primate remains. Brain, C.K., 1981. The Hunters or the Hunted? An Introduction to African Cave Taphonomy. University of Chicago Press, Chicago suggested that these primate subassemblages might have resulted from a focus by carnivores on primate predation and bone accumulation. Brain's hypothesis prompted us to investigate, in a previous study, this taphonomic issue as it relates to density-mediated destruction of primate bones (J. Archaeol. Sci. 29, 2002, 883). Here we extend our investigation of Brain's hypothesis by examining additional intrinsic qualities of baboon bones and their role as mediators of skeletal element representation in carnivore-created assemblages. Using three modern adult baboon skeletons, we collected data on four intrinsic bone qualities (bulk bone mineral density, maximum length, volume, and cross-sectional area) for approximately 81 bones per baboon skeleton. We investigated the relationship between these intrinsic bone qualities and a measure of skeletal part representation (the percentage minimum animal unit) for baboon bones in carnivore refuse and scat assemblages. Refuse assemblages consist of baboon bones not ingested during ten separate experimental feeding episodes in which individual baboon carcasses were fed to individual captive leopards and a spotted hyena. Scat assemblages consist of those baboon bones recovered in carnivore regurgitations and feces resulting from the feeding episodes. In refuse assemblages, volume (i.e., size) was consistently the best predictor of element representation, while cross-sectional area was the poorest predictor in the leopard refuse assemblage and bulk bone mineral density (i.e., a measure of the proportion of cortical to trabecular bone) was the poorest predictor in the hyena refuse assemblage. In light of previous documentation of carnivore-induced density-mediated destruction to bone assemblages, we interpret the current findings as suggestive of the secondary importance of bulk bone mineral density to other intrinsic qualities of skeletal elements (e.g., size, maximum dimension, and average cross-sectional area). It is only when skeletal elements are too large for consumption (e.g., many long bones) that they are fragmented following intra-element patterns of density-mediated carnivore destruction. There appears to be a size threshold beneath which bulk bone mineral density contributes little to mediating carnivore destruction of carcasses. Thus, depending on body size of the predator, body size of the prey, and specific size of the element, bulk bone mineral density may play little or no role of primary importance in mediating the destruction of skeletal elements. We compare patterns in modern comparative assemblages to patterns in primate fossil assemblages from Swartkrans. One of the fossil assemblages, Swartkrans Member 1, Hanging Remnant, most closely approximates a hyena (possibly refuse) assemblage pattern, while the Swartkrans Member 2 assemblage most closely approximates a leopard (possibly scat) assemblage pattern. The Swartkrans Member 1, Lower Bank, assemblage does not closely approximate any of our modern comparative assemblage patterns.     

Homogeneity of fossil assemblages extracted from mine dumps: an analysis of Plio-Pleistocene fauna from South African caves

Mine dumps associated with limestone cave deposits are common in dolomitic areas of southern Africa. The dumps often contain blocks of breccia, which are rich in micro-mammalian fossils (especially rodents, shrews and bats). Unfortunately, these fossiliferous breccia blocks are out of geological and stratigraphic context. Nevertheless, they provide a large amount of palaeontological material of great interest. In order to use this kind of material, a first approach is to test for homogeneity of the fossil assemblages extracted from the breccia blocks. Fisher's exact test can be used. Two analyses were undertaken. The first was performed on block samples taken in situ from breccia at the Drimolen hominid site. The results indicated that the samples were homogenous, as expected. The second analysis was carried out on different samples extracted from blocks of breccia collected from a dump at the Gondolin site. The results show that it is possible to group several samples in a single representative assemblage. Some blocks could be grouped together and then used to address taphonomic issues. Once these problems are solved, the data set can be used with greater confidence to address matters concerning palaeoenvironmental reconstructions associated with Plio-Pleistocene hominids.     

Eocene fossil rodent assemblages from the Erlian Basin (Inner Mongolia,China): Biochronological implications

Rodents from the Nuhetingboerhe-Huheboerhe area in the Erlian Basin, Inner Mongolia, differ stratigraphically: primitive ctenodactyloids such as Chenomys and Yuanomys are dominant in the upper part of the Nomogen Formation; Tamquammys dominates in the Arshanto Formation; Asiomys, Pappocricetodon, and Yuomys appear in the lower part of the Irdin Manha Formation and Tamquammys is rarer in this formation than in the Arshanto Formation. The assemblage of the upper part of the Nomogen Formation is similar to that of the Lingcha Formation of Hunan, the Wutu Formation of Shandong, the Yuhuangding Formation of Hubei, and the Bumban Member of the Nara-Bulak Formation of Mongolia. The assemblage in the upper part of the Arshanto Formation is correlated with that from the locality Andarak 2 in Kyrgyzstan. The assemblage from the lower part of the Irdin Manha Formation resembles that of the lower part of the Hetaoyuan Formation of Henan.On the basis of the comparison of the rodent assemblages, I consider that the age of upper part of the Nomogen Formation corresponds to the Bumbanian land mammal age. The Bumbanian, Arshantan, and Irdinmanhan land mammal ages are correlated respectively to the early Ypresian, the middle–late Ypresian, and the early Lutetian of the Geological Time Scale. The Bumbanian and Irdinmanhan land mammal ages are also correlated to the early Wasatchian and the early Uintan (or the later Bridgerian) of the North American Land Mammal Ages.     

Floristic turnover in Iceland from 15 to 6 Ma – extracting biogeographical signals from fossil floral assemblages

Aim This study aims to document the floristic changes that occurred in Iceland between 15 and 6 Ma and to establish the dispersal mechanisms for the plant taxa encountered. Using changing patterns of dispersal, two factors controlling floristic changes are tested. Possible factors are (1) climate change, and (2) the changing biogeography of Iceland over the time interval studied; that is, the presence or absence of a Miocene North Atlantic Land Bridge. Location The North Atlantic. Methods Species lists of fossil plants from Iceland in the time period 15 to 6 Ma were compiled using published data and new data. Closest living analogues were used to establish dispersal properties for the fossil taxa. Dispersal mechanisms of fossil plants were then used to reconstruct how Iceland was colonized during various periods. Results Miocene floras of Iceland (15–6 Ma) show relatively high floristic turnover from the oldest floras towards the youngest; and few taxa from the oldest floras persist in the younger floras. The frequencies of the various dispersal mechanisms seen in the 15‐Ma floras are quite different from those recorded in the 6‐Ma floras, and there is a gradual change in the prevailing mode of dispersal from short‐distance anemochory and dyschory to long‐distance anemochory. Two mechanisms can be used to explain changing floral composition: (1) climate change, and (2) the interaction between the dispersal mechanisms of plants and the increasing isolation of proto‐Iceland during the Miocene. Main conclusions Dispersal mechanisms can be used to extract palaeogeographic signals from fossil floras. The composition of floras and dispersal mechanisms indicate that Iceland was connected both to Greenland and to Europe in the early Middle Miocene, allowing transcontinental migration. The change in prevalence of dispersal modes from 15 to 6 Ma appears to reflect the break‐up of a land bridge and the increasing isolation of Iceland after 12 Ma. Concurrent gradual cooling and isolation caused changes in species composition. Specifically, the widening of the North Atlantic Ocean prevented taxa with limited dispersal capability from colonizing Iceland, while climate cooling led to the extinction of thermophilous taxa.