Clive N. Trueman

Can otolith elemental chemistry retrospectively track migrations in fully marine fishes

Otolith microchemistry can provide valuable information about stock structure and mixing patterns when the magnitude of environmental differences among areas is greater than the cumulative influence of any vital effects. Here, the current understanding of the underlying mechanisms governing element incorporation into the otolith is reviewed. Hard and soft acid and base (HSAB) theory is employed to explore the differences in chemical behaviours, distributions and affinities between elements. Hard acid cations (e.g. Mg(2+) , Li(+) and Ba(2+) ) tend to be less physiologically influenced and accepted more readily into the otolith crystal lattice but are relatively homogeneous in seawater. Soft acid cations (e.g. Zn(2+) and Cu(2+) ) on the other hand, exhibit more varied distributions in seawater, but are more likely to be bound to blood proteins and less available for uptake into the otolith. The factors influencing the geographical distribution of elements in the sea, and their incorporation into the otoliths of marine fishes are reviewed. Particular emphasis is placed on examining physiological processes, including gonad development, on the uptake of elements commonly used in population studies, notably Sr. Finally, case studies are presented that either directly or indirectly compare population structuring or movements inferred by otolith elemental fingerprints with the patterns indicated by additional, alternative proxies. The main obstacle currently limiting the application of otolith elemental microchemistry to infer movements of marine fishes appears to lie in the largely homogeneous distribution of those elements most reliably measured in the otolith. Evolving technologies will improve the discriminatory power of otolith chemistry by allowing measurement of spatially explicit, low level elements; however, for the time being, the combination of otolith minor and trace element fingerprints with alternative proxies and stable isotopic ratios can greatly extend the scope of migration studies. Among the otolith elements that routinely occur above instrument detection limits, Ba, Mn and Li were deemed the most likely to prove reliable geographic markers in marine species.

Rare earth element geochemistry and taphonomy of terrestrial vertebrate assemblages

Most taphonomic analyses of vertebrate remains have focused upon physical processes. Chemical processes only rarely are addressed, leaving a large untapped store of quantitative taphonomic information contained within the bones themselves. In this paper, the rare earth element (REE) signature of fossil bones in terrestrial deposits is shown to be controlled by the early diagenetic environment. Thus, bones fossilized in different early diagenetic environments may be separated by their distinct REE signatures. Furthermore, the variation of REE patterns developed in individual bones within an assemblage is controlled by sedimentologic and taphonomic processes. Hence, the degree of mixing and reworking (relative time and space averaging) of vertebrate elements within a particular assemblage may be determined from the REE patterns of the interred bones. REE geochemistry represents a new and powerful taphonomic tool.

Dinosaurs and other fossil vertebrates from fluvial deposits in the Lower Cretaceous of southern Tunisia

Remains of dinosaurs and other vertebrates (sharks, bony fishes, coelacanths, turtles, crocodilians, pterosaurs) are reported from the Chenini Formation of the Tataouine region in southern Tunisia. The Formation is part of the ‘continental intercalaire’, a succession of continental deposits of Early to Late Cretaceous age distributed over the whole of North Africa and the Sahara. It consists of bar and channel deposits of broad rivers that flowed NNW from the mid-Sahara region towards the southern shore of Tethys. Dinosaur-bearing units in the ‘continental intercalaire’ have been dated to the Hauterivian to Cenomanian, and the Chenini Formation is possibly Albian in age. Dinosaur fossils include abundant teeth of the theropods Carcharodontosaurus and Spinosaurus, as well as postcranial elements of theropods and a medium-sized sauropod. A tooth of an ornithocheirid is the first report of a pterosaur from the region. The dinosaur bones and teeth were transported some distance and deposited in a channel lag, associated with less damaged locally derived material such as fern fronds, coprolites, fish teeth and scales, and crocodilian scutes.

A nesting trace with eggs for the Cretaceous theropod dinosaur Troodon formosus

ABSTRACT An unusual trace containing eggs of the 50 kg-plus theropod dinosaur, Troodon formosus, represents one of the best preserved dinosaur nests. This unique specimen (MOR 963) represents the actual nest structure and the direct product of Troodon behavior. The trace comes from the Campanian, Late Cretaceous Two Medicine Formation of Montana, and consists of a bowl-shaped depression with an internal area of ~1m2 surrounded by a distinct rim. A clutch of 24 tightly-placed eggs sat in the center and both nest and clutch show bilateral symmetry about a north–south axis. The trace occurs within a moderately well-developed micritic paleosol. A physically and chemically distinct mudstone covered the nest and represents overbank deposition. The nest protected the eggs by creating a suitable micro-environment during the lengthy egg-laying and incubation periods. Clutch and nest size, shape, and symmetry and low organic carbon of the overlying mudstone suggests brooding rather than incubation with vegetative c...

Visualizing fossilization using laser ablation-inductively coupled plasma-mass spectrometry maps of trace elements in Late Cretaceous bones

Elemental maps generated by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) provide a previously unavailable high-resolution visualization of the complex physicochemical conditions operating within individual bones during the early stages of diagenesis and fossilization. A selection of LA-ICP-MS maps of bones collected from the Late Cretaceous of Montana (United States) and Madagascar graphically illustrate diverse paths to recrystallization, and reveal unique insights into geochemical aspects of taphonomic history. Some bones show distinct gradients in concentrations of rare earth elements and uranium, with highest concentrations at external bone margins. Others exhibit more intricate patterns of trace element uptake related to bone histology and its control on the flow paths of pore waters. Patterns of element uptake as revealed by LA-ICP-MS maps can be used to guide sampling strategies, and call into question previous studies that hinge upon localized bulk samples of fossilized bone tissue. LA-ICP-MS maps also allow for comparison of recrystallization rates among fossil bones, and afford a novel approach to identifying bones or regions of bones potentially suitable for extracting intact biogeochemical signals.

Locations of marine animals revealed by carbon isotopes

Knowing the distribution of marine animals is central to understanding climatic and other environmental influences on population ecology. This information has proven difficult to gain through capture-based methods biased by capture location. Here we show that marine location can be inferred from animal tissues. As the carbon isotope composition of animal tissues varies with sea surface temperature, marine location can be identified by matching time series of carbon isotopes measured in tissues to sea surface temperature records. Applying this technique to populations of Atlantic salmon (Salmo salar L.) produces isotopically-derived maps of oceanic feeding grounds, consistent with the current understanding of salmon migrations, that additionally reveal geographic segregation in feeding grounds between individual philopatric populations and age-classes. Carbon isotope ratios can be used to identify the location of open ocean feeding grounds for any pelagic animals for which tissue archives and matching records of sea surface temperature are available.

Identifying migrations in marine fishes through stable‐isotope analysis

The isotopic composition of many elements varies across both land and ocean surfaces in a predictable fashion. These stable-isotope ratios are transferred into animal tissues, potentially providing a powerful natural geospatial tag. To date, most studies using stable isotopes as geolocators in marine settings have focussed on mammals and seabirds conducting large ocean-basin scale migrations. An increasing understanding of isotopic variation in the marine environment, and improved sampling and analytical techniques, however, means that stable isotopes now hold genuine promise as a natural geolocation tag in marine fishes. Here, the theoretical background underpinning the use of stable isotopes of C, N and O in otolith, scale and muscle tissues as geolocation tools in the marine environment is reviewed, and examples of their applications are provided.

Geochemical taphonomy of shallow marine vertebrate assemblages

Abstract Combined histological and geochemical analyses demonstrate complex processes leading to preservation of microbially altered bone. In certain situations, a chemical microenvironment distinct from surrounding pore waters is developed and maintained within the bone. The bone acts as a closed system, and hence palaeoenvironmental interpretations based on fossil bone apatite chemistry may not accurately reflect overall geochemical conditions of the sedimentary deposits where the bones were buried. Geochemical techniques based on variance in trace element compositions of bones from different assemblages can be used as a measure of the relative degree of mixing or taphonomic averaging within marine vertebrate assemblages.

Rare earth elements in Solnhofen biogenic apatite: geochemical clues to the palaeoenvironment

Rare earth element (REE) concentrations in biogenic apatite samples (coprolite, bone and soft-tissue) were used to investigate the environment of deposition of the celebrated Solnhofen fossil Lagerstatten. The measured REE patterns are similar between different localities, lithologies (flinz, faule) and levels in the Upper Solnhofen Plattenkalk, suggestive of a stable REE supply during deposition. The behaviour of cerium in the Solnhofen samples implies that bottom water conditions were not anoxic, and variations in the cerium anomaly can be explained by differences in burial rate. These results provide further geochemical support for current depositional models [Barthel, K.W., 1978. Solnhofen: Ein Blick in die Erdgeschichte. Ott Verlag, Thun.; Barthel, K.W., Swinburne, N.H.M., Conway Morris, S., 1990, Solnhofen. A Study in Mesozoic Palaeontology. Cambridge Univ. Press, Cambridge.] that propose that extra-basinal processes are responsible for the interbedded nature of the Solnhofen deposits, rather than intra-basinal processes such as water turnover events.

Trophic interactions of fish communities at midwater depths enhance long-term carbon storage and benthic production on continental slopes

Biological transfer of nutrients and materials between linked ecosystems influences global carbon budgets and ecosystem structure and function. Identifying the organisms or functional groups that are responsible for nutrient transfer, and quantifying their influence on ecosystem structure and carbon capture is an essential step for informed management of ecosystems in physically distant, but ecologically linked areas. Here, we combine natural abundance stable isotope tracers and survey data to show that mid-water and bentho-pelagic-feeding demersal fishes play an important role in the ocean carbon cycle, bypassing the detrital particle flux and transferring carbon to deep long-term storage. Global peaks in biomass and diversity of fishes at mid-slope depths are explained by competitive release of the demersal fish predators of mid-water organisms, which in turn support benthic fish production. Over 50% of the biomass of the demersal fish community at depths between 500 and 1800 m is supported by biological rather than detrital nutrient flux processes, and we estimate that bentho-pelagic fishes from the UK–Irish continental slope capture and store a volume of carbon equivalent to over 1 million tonnes of CO2 every year.