The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Past episodes of greenhouse warming provide insight into the coupling of climate and the carbon cycle and thus may help to predict the consequences of unabated carbon emissions in the future.

/pdf/an-early-cenozoic-perspective-on-greenhouse-warming-and-yffl0bpyf1.pdf

An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics

Fire is a worldwide phenomenon that appears in the geological record soon after the appearance of terrestrial plants. Fire influences global ecosystem patterns and processes, including vegetation distribution and structure, the carbon cycle, and climate. Although humans and fire have always coexisted, our capacity to manage fire remains imperfect and may become more difficult in the future as climate change alters fire regimes. This risk is difficult to assess, however, because fires are still poorly represented in global models. Here, we discuss some of the most important issues involved in developing a better understanding of the role of fire in the Earth system.

/pdf/fire-in-the-earth-system-481yvwaoo1.pdf

Fire in the Earth System

The second edition of The Biomarker Guide is a fully updated and expanded version of this essential reference. Now in two volumes, it provides a comprehensive account of the role that biomarker technology plays both in petroleum exploration and in understanding Earth history and processes. Biomarkers and Isotopes in the Environment and Human History details the origins of biomarkers and introduces basic chemical principles relevant to their study. It discusses analytical techniques, and applications of biomarkers to environmental and archaeological problems. The Biomarker Guide is an invaluable resource for geologists, petroleum geochemists, biogeochemists, environmental scientists and archaeologists.

The Biomarker Guide

Bones of recent mammals in the Amboseli Basin, southern Kenya, exhibit distinctive weathering characteristics that can be related to the time since death and to the local conditions of temperature, humidity and soil chemistry. A categorization of weathering characteristics into six stages, recognizable on descriptive criteria, provides a basis for investigation of weathering rates and processes. The time necessary to achieve each successive weathering stage has been calibrated using known-age carcasses. Most bones decompose beyond recognition in 10 to 15 yr. Bones of animals under 100 kg and juveniles appear to weather more rapidly than bones of large animals or adults. Small-scale rather than widespread environmental factors seem to have greatest influence on weathering characteristics and rates. Bone weathering is potentially valuable as evidence for the period of time represented in recent or fossil bone assemblages, in- cluding those on archeological sites, and may also be an important tool in censusing populations of animals in modern ecosystems.

Taphonomic and Ecologic Information Form Bone Weathering

Biomarkers for methane cycling: From marine to terrestrial settings

The Eocene Arctic Azolla phenomenon: species composition, temporal range and geographic extent.

The carbon isotope stratigraphy of the PETM—New records from bacterial and higher plant biomarkers

Catastrophic vegetation changes

Hilton et al. (2016) assert that our identification and dating of Pinus mundayi from the Cretaceous (Valanginian, 140–133 Ma) of Nova Scotia (Falcon-Lang et al., 2016) is unreliable, and argue that P. yorkshirensis, a species that they earlier described (Ryberg et al., 2012) is actually the oldest pine fossil. In their paper, the age of P. yorkshirensis is given as Early Cretaceous, and close to the Barremian–Hauterivian boundary (ca. 131–129 Ma). However, in Ryberg et al.’s figure 1, the fossil is shown straddling the Hauterivian–Valanginian boundary (ca. 133 Ma). In their abstract (Ryberg et al., 2012) the fossil is said to derive from the Wealden Formation of Yorkshire, UK, although this stratigraphic unit is absent in that region. The reasons for these inconsistencies relate to uncertain provenance. Ryberg et al. found the specimen in the Lapworth Museum, Birmingham, UK, in six pieces, with a label reading ‘Yorkshire Jurassic cone,’ but without any other accession information. To determine the age of P. yorkshirensis, Ryberg et al. obtained a ‘poor to fair’ assemblage of dinoflagellates (not illustrated) from one fragment, including Callaiosphaeridium asymmetricum, ?Cribroperidinium confossum, and Odontochitina operculata. As biozones can be diachronous, they assumed correct locality data on the specimen label (Yorkshire). Compared to Yorkshire reference sections, the assemblage was considered indicative of an Early Cretaceous, Barremian–Hauterivian boundary age. However, this inference required that the age data on the specimen label (Jurassic) was incorrect. A Barremian–Hauterivian boundary age in Yorkshire indicates an origin in the Speeton Clay Formation (SCF), a unit that is time-equivalent to the Wealden Formation of the southern UK; hence, presumably, the incorrect use of that unit in the abstract. Only one seed cone has been, hitherto, reported from the SCF (Pearce, 1982). Crucially, this cone is pyritized, as is almost all SCF fossil plant material, whereas P. yorkshirensis is sideritized. While an origin in the SCF cannot be excluded, the absence of fossil plant material with similar preservation to P. yorkshirensis is concerning. If the age is incorrect, so also may be the locality on the specimen label (Yorkshire). The dinoflagellate assemblage could be indicative of a wider age range. Globally, C. asymmetricum and O. operculata have a Cretaceous (Valanginian) to early Paleogene (Eocene) range; C. confossum is the only taxon with a narrower Hauterivian–Barremian range (Dinoflagellate Database; www.paleobotany.ru). However, Ryberg et al. note that the identification of ?Cribroperidinium confossum is uncertain. A Hauterivian– Barremian boundary age for P. yorkshirensis is one scenario assuming a Yorkshire provenance and correct identification of C. confossum; the alternative scenario is a Cretaceous (Valanginian) to early Paleogene (140– 34 Ma) age. In spite of the approaches employed by Ryberg et al., we consider that their claim that P. yorkshirensis is the oldest known pine fossil is unreliable. Specimens discovered in museum drawers without accession history have led to paleobotanical errors in the past. Stopes (1913) described an unaccessioned specimen in the Natural History Museum, London, as Woburnia, and argued that it was, then, the oldest (Cretaceous, Aptian) angiosperm. Stopes’ findings were criticized, and analogous techniques to those of Ryberg et al. were employed to better constrain age and provenance, and Woburnia is now considered as being from the Neogene of Indonesia (Casey, 1961). Turning to the disputed identity and age of our own fossils of P. mundayi, an interesting anomaly, to which Hilton et al. draw attention, is the absence, in P. mundayi, of ray tracheids, a feature common to all extant Pinus. We are uncertain if this is a genuine absence or an apparent absence due to limited options for observing rays; if the former, this suggests that, in its early evolution, Pinus had not yet acquired all the apomorphic characters of the modern genus. As Hilton et al. point out, this raises questions regarding how we distinguish between Pinus and Pinus-like taxa in the fossil record, be they long-shoots, seed cones, or some other organ. Multiple non-diagnostic characters are listed by Hilton et al. (their supplemental table), but P. mundayi does have characters diagnostic of Pinus. The occurrence of normal resin ducts in the secondary xylem and phloem that show thin-walled epithelial cell walls is highly characteristic of Pinus, but also found occasionally in some juvenile Picea. Hilton et al. state that this feature is also present in Larix and Pseudotsuga, but they do not provide any evidence, and their view contradicts other sources (e.g., Esteban et al., 2004). Further, they failed to comment on the occurrence of axial ducts in the phloem of P. mundayi, a feature that excludes Cathaya, Picea, and Pseudotsuga (Lin et al., 2002). Our material also shows fenestriform and pinoid cross-field pitting, a character that is diagnostic of Pinus (Esteban et al., 2004). Taphonomic studies do show that the shape of cross-field pits may significantly change during charring but, as we stated, we had allowed for this, and in other taxa from the same assemblage, different (e.g., cupressoid) original pit structure is faithfully preserved. A third diagnostic character is the presence of short-shoots that distally diverge into two separate bundles. We interpreted these features as evidence that P. mundayi was a two-needle pine. Hilton et al. state that we have “structurally misinterpreted” these features; however, the bundles show very close anatomical comparison with the short-shoots of two-needle pines at the periphery of the wood (Dorken et al., 2010), supporting our interpretation. A final issue that Hilton et al. raise is the age of P. mundayi. As with all biostratigraphic interpretations, age is a question of likelihood. The most parsimonious interpretation is a Valanginian (140–133 Ma) age based on palynological assemblage comparison with proximal basins of the nascent Atlantic Ocean. A Valanginian–Hauterivian (140–129 Ma) age is possible, if comparison with more distal western Canadian sites is included. Least likely, due to lack of angiosperm pollen, is a Valanginian–Barremian (140–125 Ma) range, though this is Hilton et al.’s preference. In our opinion, the age of P. mundayi is known with greater certainty than that of P. yorkshirensis, which Hilton et al. argue is the oldest known pine. Therefore, we reaffirm Pinus mundayi as the oldest known pine, and emphasize its preservation as charcoal, which may suggest that fire played a key role in the early evolution of the genus.

/pdf/reaffirming-pinus-mundayi-as-the-oldest-known-pine-fossil-3yzujhlgkv.pdf

Margaret E. Collinson

Papers

Biomarkers for methane cycling: From marine to terrestrial settings

The Eocene Arctic Azolla phenomenon: species composition, temporal range and geographic extent.

The carbon isotope stratigraphy of the PETM—New records from bacterial and higher plant biomarkers

Catastrophic vegetation changes

Reaffirming Pinus mundayi as the oldest known pine fossil: REPLY