Thomas Tütken

Biology of the sauropod dinosaurs: the evolution of gigantism

The herbivorous sauropod dinosaurs of the Jurassic and Cretaceous periods were the largest terrestrial animals ever, surpassing the largest herbivorous mammals by an order of magnitude in body mass. Several evolutionary lineages among Sauropoda produced giants with body masses in excess of 50 metric tonnes by conservative estimates. With body mass increase driven by the selective advantages of large body size, animal lineages will increase in body size until they reach the limit determined by the interplay of bauplan, biology, and resource availability. There is no evidence, however, that resource availability and global physicochemical parameters were different enough in the Mesozoic to have led to sauropod gigantism.

Body temperatures of modern and extinct vertebrates from ^(13)C-^(18)O bond abundances in bioapatite

The stable isotope compositions of biologically precipitated apatite in bone, teeth, and scales are widely used to obtain information on the diet, behavior, and physiology of extinct organisms and to reconstruct past climate. Here we report the application of a new type of geochemical measurement to bioapatite, a “clumped-isotope” paleothermometer, based on the thermodynamically driven preference for 13C and 18O to bond with each other within carbonate ions in the bioapatite crystal lattice. This effect is dependent on temperature but, unlike conventional stable isotope paleothermometers, is independent from the isotopic composition of water from which the mineral formed. We show that the abundance of 13C-18O bonds in the carbonate component of tooth bioapatite from modern specimens decreases with increasing body temperature of the animal, following a relationship between isotope “clumping” and temperature that is statistically indistinguishable from inorganic calcite. This result is in agreement with a theoretical model of isotopic ordering in carbonate ion groups in apatite and calcite. This thermometer constrains body temperatures of bioapatite-producing organisms with an accuracy of 1–2 °C. Analyses of fossilized tooth enamel of both Pleistocene and Miocene age yielded temperatures within error of those derived from similar modern taxa. Clumped-isotope analysis of bioapatite represents a new approach in the study of the thermophysiology of extinct species, allowing the first direct measurement of their body temperatures. It will also open new avenues in the study of paleoclimate, as the measurement of clumped isotopes in phosphorites and fossils has the potential to reconstruct environmental temperatures.

Glacial–interglacial cycles in Sr and Nd isotopic composition of Arctic marine sediments triggered by the Svalbard/Barents Sea ice sheet

Sr and Nd isotopic compositions of Arctic marine sediments characterize changes of sediment source regions and trace shelf–ocean particle pathways during glacial–interglacial transitions in the eastern Arctic Ocean. In the 140-ka sedimentary record of a marine core from Yermak Plateau, north of Svalbard, 87Sr/86Sr ratios and eNd values vary between 0.717 and 0.740 and −9.3 and −14.9, respectively. Sr and Nd isotopic composition both change characteristically during glacial–interglacial cycles and are correlated with the extension of the Svalbard/Barents Sea ice sheet (SBIS). The downcore variation in Sr and Nd isotopic composition indicates climatically induced changes in sediment provenance from two isotopically distinct end-members: (1) Eurasian shelf sediments as a distal source; and (2) Svalbard bedrock as a proximal source that coincide with a change in transport mechanism from sea ice to glacial ice. During glacier advance from Svalbard and intensified glacial bedrock erosion, eNd values decrease gradually to a minimum value of −14.9 due to increased input of crystalline Svalbard bedrock material. During glacial maxima, the SBIS covered the entire Barents Sea shelf and supplied increasing amounts of Eurasian shelf material to the Arctic Ocean as ice rafted detritus (IRD). eNd values in glacial sediments reach maximum values that are comparable to the average value of modern Eurasian shelf and sea ice sediments (eNd=−10.3). This confirms ice rafting as a major sediment transport mechanism for Eurasian shelf sediments into the Arctic Ocean and trace a sediment origin from the Kara Sea/Laptev Sea shelf area. After the decay of the shelf-based SBIS, the glacial shelf sediment spikes during glacial terminations I (eNd=−10.6) and II (eNd=−10.1) eNd values rapidly decrease to values of −12.5 typical for interglacial averages. The downcore Sr isotopic composition is anticorrelated to the Nd isotopic composition, but may be also influenced by grain-size effects. In contrast, the Nd isotopic composition in clay- to silt-size fractions of one bulk sediment sample is similar to within 0.3–0.8 eNd units and seems to be a grain-size independent provenance tracer.

Dinosaur Body Temperatures Determined from Isotopic (13C-18O) Ordering in Fossil Biominerals

Large dinosaurs had body temperatures similar to those of modern mammals and birds. The nature of the physiology and thermal regulation of the nonavian dinosaurs is the subject of debate. Previously, arguments have been made for both endothermic and ectothermic metabolisms on the basis of differing methodologies. We used clumped isotope thermometry to determine body temperatures from the fossilized teeth of large Jurassic sauropods. Our data indicate body temperatures of 36° to 38°C, which are similar to those of most modern mammals. This temperature range is 4° to 7°C lower than predicted by a model that showed scaling of dinosaur body temperature with mass, which could indicate that sauropods had mechanisms to prevent excessively high body temperatures being reached because of their gigantic size.

Oxygen and Carbon Isotope Variations in a Modern Rodent Community – Implications for Palaeoenvironmental Reconstructions

Background The oxygen (δ18O) and carbon (δ13C) isotope compositions of bioapatite from skeletal remains of fossil mammals are well-established proxies for the reconstruction of palaeoenvironmental and palaeoclimatic conditions. Stable isotope studies of modern analogues are an important prerequisite for such reconstructions from fossil mammal remains. While numerous studies have investigated modern large- and medium-sized mammals, comparable studies are rare for small mammals. Due to their high abundance in terrestrial ecosystems, short life spans and small habitat size, small mammals are good recorders of local environments. Methodology/Findings The δ18O and δ13C values of teeth and bones of seven sympatric modern rodent species collected from owl pellets at a single locality were measured, and the inter-specific, intra-specific and intra-individual variations were evaluated. Minimum sample sizes to obtain reproducible population δ18O means within one standard deviation were determined. These parameters are comparable to existing data from large mammals. Additionally, the fractionation between coexisting carbonate (δ18OCO3) and phosphate (δ18OPO4) in rodent bioapatite was determined, and δ18O values were compared to existing calibration equations between the δ18O of rodent bioapatite and local surface water (δ18OLW). Specific calibration equations between δ18OPO4 and δ18OLW may be applicable on a taxonomic level higher than the species. However, a significant bias can occur when bone-based equations are applied to tooth-data and vice versa, which is due to differences in skeletal tissue formation times. δ13C values reflect the rodents’ diet and agree well with field observations of their nutritional behaviour. Conclusions/Significance Rodents have a high potential for the reconstruction of palaeoenvironmental conditions by means of bioapatite δ18O and δ13C analysis. No significant disadvantages compared to larger mammals were observed. However, for refined palaeoenvironmental reconstructions a better understanding of stable isotope signatures in modern analogous communities and potential biases due to seasonality effects, population dynamics and tissue formation rates is necessary.

Tracking Cats: Problems with Placing Feline Carnivores on δ18O, δD Isoscapes

Background Several felids are endangered and threatened by the illegal wildlife trade. Establishing geographic origin of tissues of endangered species is thus crucial for wildlife crime investigations and effective conservation strategies. As shown in other species, stable isotope analysis of hydrogen and oxygen in hair (δDh, δ18Oh) can be used as a tool for provenance determination. However, reliably predicting the spatial distribution of δDh and δ18Oh requires confirmation from animal tissues of known origin and a detailed understanding of the isotopic routing of dietary nutrients into felid hair. Methodology/Findings We used coupled δDh and δ18Oh measurements from the North American bobcat (Lynx rufus) and puma (Puma concolor) with precipitation-based assignment isoscapes to test the feasibility of isotopic geo-location of felidae. Hairs of felid and rabbit museum specimens from 75 sites across the United States and Canada were analyzed. Bobcat and puma lacked a significant correlation between H/O isotopes in hair and local waters, and also exhibited an isotopic decoupling of δ18Oh and δDh. Conversely, strong δD and δ18O coupling was found for key prey, eastern cottontail rabbit (Sylvilagus floridanus; hair) and white-tailed deer (Odocoileus virginianus; collagen, bone phosphate). Conclusions/Significance Puma and bobcat hairs do not adhere to expected pattern of H and O isotopic variation predicted by precipitation isoscapes for North America. Thus, using bulk hair, felids cannot be placed on δ18O and δD isoscapes for use in forensic investigations. The effective application of isotopes to trace the provenance of feline carnivores is likely compromised by major controls of their diet, physiology and metabolism on hair δ18O and δD related to body water budgets. Controlled feeding experiments, combined with single amino acid isotope analysis of diets and hair, are needed to reveal mechanisms and physiological traits explaining why felid hair does not follow isotopic patterns demonstrated in many other taxa.

Does body mass convey a digestive advantage for large herbivores

Summary 1. A key concept of body mass (BM) in niche separation of large herbivores assumes that the decrease in diet quality inherent to increasing BM (due to less selective feeding behaviour) is balanced by a simultaneous increase in digestive ability (due to longer retention times), resulting in no or less-than-expected reduction in digestibility (as measured in the animal as a result of diet quality and digestive ability). However, the second part of this concept has been challenged recently due to theoretical problems and mismatch with empirical data. 2. A proxy for digestibility, such as metabolic faecal nitrogen (MFN), will comprise both information on diet quality and digestive ability in free-ranging animals. In captive animals, if diet is kept constant, such a proxy can exclusively indicate digestive ability. Comparing freeranging and captive animals under such conditions, one would expect an increase in MFN with BM in captive animals and no relationship between these measures in free-ranging animals if BM was related to digestive ability. 3. We compared captive ungulates on a consistent grass hay diet (17 species; 30–4000 kg BM) to a sample of free-ranging East African ungulates (19 species; 12–4000 kg BM). MFN was used as the major proxy for digestibility. 4. In captive animals, there was no influence of BM on MFN (P =0 � 466); for free-ranging animals, a significant decreasing effect of body mass on MFN (P =0 � 002) and therefore diet quality was found at a scaling of BM � 0� 15 . 5. In conclusion, scenarios that assume a compensation of the evident decrease in diet quality with BM via an increased digestive ability are not supported by this study. This does not rule out other feeding-related factors in facilitating large BM, such as compensation by an increased diet intake.

Surface-water freshening and high-latitude river discharge in the Eocene North Sea

Abstract: A shark-tooth apatite δ18O record of the early Palaeogene North Sea reflects changes in regional hydrography by showing variable temperatures and salinities. A 2–4 Ma period in the early Eocene was particularly influenced by substantial surface-water freshening, indicated by a 3–4‰ reduction of δ18O values. The magnitude of the δ18O decrease indicates a depletion in 18O of surface waters by 2–3‰ relative to Eocene mean ocean water. This value is lower than that of coeval lakes reconstructed from freshwater gastropod δ18O values from the Paris Basin, suggesting that large rivers with high-latitude catchment areas drained into the North Sea. The period of surface-water freshening began close to the Palaeocene – Eocene thermal maximum, when relative sea-level fall, tectonic uplift and basaltic volcanism caused a temporary isolation of the North Sea. North Atlantic and North Sea surface waters became reconnected during a series of early Eocene transgressions.

Oxygen isotope analysis of human bone phosphate evidences weaning age in archaeological populations

Here we report bone phosphate oxygen (δ(18)Op) values from perinates/neonates and infants (<3.5 years; n = 32); children (4-12 years; n = 12); unsexed juveniles (16-18 years; n = 2); and adult bones (n = 17) from Wharram Percy, North Yorkshire, England, in order to explore the potential of this method to investigate patterns of past breastfeeding and weaning. In prior studies, δ(15)N and δ(13)C analyses of bone collagen have been utilized to explore weaning age in this large and well-studied assemblage, rendering this material highly appropriate for the testing and development of this alternative method targeting the inorganic phase of bone. Data produced reveal (18)O-enrichment in the youngest perinatal/neonatal and infant samples, and an association between age and bone δ(18)Op (and previously-published δ(15)N values), with high values in both these isotope systems likely due to breastfeeding. After the age of 2-3 years, δ(18)Op values are lower, and all children between the ages of 4 and 12, along with the vast majority of sub-adults and adults sampled (aged 16 to >50 years), have δ(18)Op values consistent with the consumption of local modern drinking water. The implications of this study for the reconstruction of weaning practices in archaeological populations are discussed, including variations observed with bone δ(15)Ncoll and δ(18)Op co-analysis and the influence of culturally-modified drinking water and seasonality. The use of this method to explore human mobility and palaeoclimatic conditions are also discussed with reference to the data presented.

Opportunistic Feeding Strategy for the Earliest Old World Hypsodont Equids: Evidence from Stable Isotope and Dental Wear Proxies

Background The equid Hippotherium primigenium, with moderately hypsodont cheek teeth, rapidly dispersed through Eurasia in the early late Miocene. This dispersal of hipparions into the Old World represents a major faunal event during the Neogene. The reasons for this fast dispersal of H. primigenium within Europe are still unclear. Based on its hypsodonty, a high specialization in grazing is assumed although the feeding ecology of the earliest European hipparionines within a pure C3 plant ecosystem remains to be investigated. Methodology/Principal Findings A multi-proxy approach, combining carbon and oxygen isotopes from enamel as well as dental meso- and microwear analyses of cheek teeth, was used to characterize the diet of the earliest European H. primigenium populations from four early Late Miocene localities in Germany (Eppelsheim, Höwenegg), Switzerland (Charmoille), and France (Soblay). Enamel δ13C values indicate a pure C3 plant diet with small (<1.4‰) seasonal variations for all four H. primigenium populations. Dental wear and carbon isotope compositions are compatible with dietary differences. Except for the Höwenegg hipparionines, dental microwear data indicate a browse-dominated diet. By contrast, the tooth mesowear patterns of all populations range from low to high abrasion suggesting a wide spectrum of food resources. Conclusions/Significance Combined dental wear and stable isotope analysis enables refined palaeodietary reconstructions in C3 ecosystems. Different H. primigenium populations in Europe had a large spectrum of feeding habits with a high browsing component. The combination of specialized phenotypes such as hypsodont cheek teeth with a wide spectrum of diet illustrates a new example of the Liem’s paradox. This dietary flexibility associated with the capability to exploit abrasive food such as grasses probably contributed to the rapid dispersal of hipparionines from North America into Eurasia and the fast replacement of the brachydont equid Anchitherium by the hypsodont H. primigenium in Europe.