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1. Bomb pulse 14C evidence for consistent remodeling rates of cortical femur collagen in middle‐late adulthood

   https://doi.org/10.1002/ajpa.24887  

   Quinn, Rhonda L. ( January 2024 , American Journal of Biological Anthropology)

   Bomb pulse (BP) radiocarbon (¹⁴C) dating methods are used by forensic anthropologists to estimate the year‐of‐death (YOD) of unidentified individuals. Method resolution and accuracy depend on establishing lag times, or the difference between a tissue's BP¹⁴C‐derived year and the YOD, of various tissue types from known deceased persons. Bone lag times span many years and are thought to increase with age as a function of slowing remodeling rates. However, remodeling rates for various skeletal elements, bone structures and phases are not well known.

   Here a simple method is used to estimate bone remodeling rates from a compilation of published cortical femur bone collagen BP¹⁴C measurements (n = 102). Linear regression models and nonparametric tests are used to detect changes in lag times and remodeling rates with increasing age‐at‐death.

   Remodeling rates and lag times of 3.5%/year and 29 years, respectively, are estimated from individuals aged 40–97 years. In contrast to previous work, the analysis yielded modest and negligible changes in remodeling rates and lag times with advancing age. Moreover, statistically significant differences in remodeling rates and lag times were not found between reported females and males.

   Implications for the temporal contexts within an individual's lifetime of biogeochemical data in archaeology and forensic anthropology are discussed, warranting additional BP¹⁴C studies of known individuals and integration with histomorphometric analysis.

    

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2. What can hippopotamus isotopes tell us about past distributions of C 4 grassy biomes on Madagascar?

   https://doi.org/10.1002/ppp3.10402  

   Crowley, Brooke Erin ; Godfrey, Laurie Rohde ; Samonds, Karen Elizabeth ( July 2023 , PLANTS, PEOPLE, PLANET)

   Today, expansive C₄grassy biomes exist across central, western, and northern Madagascar. Some researchers have argued that the island's now‐extinct pygmy hippopotamuses belonged to a megaherbivore grazing guild that maintained these grasslands prior to human arrival. However, the chemistry of hippo bones indicates that C₄grasses were only a minor part of hippo diet. This, in turn, suggests that C₄grasses were present but not widespread when hippos were alive and that grasses expanded only after Malagasy people shifted from hunting and foraging to agropastoralism approximately 1000 years ago. These results have important implications for environmental reconstructions and biodiversity management.

   Extinct hippopotamuses (Hippopotamusspp.) were part of Madagascar's megaherbivore guild. Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes in radiometrically dated bone collagen track spatial and temporal variation in diet and habitat. If hippos helped maintain C₄grassy biomes, then they should have regularly consumed C₄grasses, which have high δ¹³C values. However, if expansive C₄grassy biomes are anthropogenic, then forests would have been more extensive in the past, and hippos would have predominantly consumed C₃plants with low δ¹³C values. Nitrogen isotopes can clarify foraging habitat (moist or dry).

   We assessed δ¹³C and δ¹⁵N values for hippos from different ecoregions of Madagascar and compared these with data for extinct herbivorous lemurs from the same ecoregions. We further explored the effects of wet/dry transitions on isotopic trends for hippos from the central highlands and spiny thicket ecoregions.

   Carbon isotopes suggest (1) limited C₄consumption by hippos in the central highlands, dry deciduous forest, and succulent woodland ecoregions; and (2) moderate consumption of C₄resources in the spiny thicket. Nitrogen data indicate that hippos foraged in wetter habitats than sympatric lemurs in all regions.

   Malagasy hippos did not regularly graze C₄grasses in dry, open habitats, even in regions blanketed by C₄grassy biomes today. Malagasy grasses are adapted to grazing and fire, but these are likely ancient adaptations that accompanied grasses when they initially spread to Madagascar. C₄grassy biomes were spatially limited in extent in the past and only expanded after the Late Holocene introduction of domesticated ungulates.

    

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3. Strategies and Discoveries Leading to the Synthesis of Trichoaurantianolide Natural Products

   https://doi.org/10.1016/B978-0-12-822212-6.00002-3  

   Williams, David R ( January 2022 , Strategies and tactics in organic synthesis)

   Harmata, Michael (Ed.)

   Several years ago, a small family of diterpenoid natural products attracted our attention as novel targets for synthesis studies. Initially, four compounds were independently characterized by the research teams of Vidari1 and Steglich.2 Trichoaurantianolides AeD (1e4 of Fig. 9.1) were isolated from fruiting bodies of the mushrooms Tricholoma aurantium and Tricholoma fracticum in 1995. Subsequent efforts of Stermer and coworkers3 described the isolation of the closely related lepistal (5) and lepistol (6) of Fig. 9.2 as the corresponding C8 deoxygenated compounds of this family. In addition, the corresponding acetate of trichoaurantianolide B was discovered and named as 6-O-aetyl- trichoaurantin (7).2 Structure assignments were based upon extensive nuclear magnetic resonance (NMR) studies, and the features of relative stereo- chemistry were confirmed by an X-ray crystallographic analysis of trichoaurantianolide B (2).1b,2 These original investigators described the trichoaurantianolides as examples of a new class of diterpenes named as neodolastanes that signified a structural relationship to the tricyclic metabo- lites of marine origins known as dolastanes as represented by dolatriol (8)4 and the clavularane 95 of Fig. 9.2. Neodolastanes were defined as substances in which the bridgehead methyl substituent appears in a vicinal relationship with respect to the isopropyl group as exemplified in 4,5-deoxyneodolabelline (10) of Fig. 9.2, a related class of marine natural products.6 Steglich and coworkers2 also indicated an assignment of absolute stereo- chemistry for 2 that was based on Hamilton’s applications of linear-hypothesis testing of crystallographic data. This seldom-used technique was in agreement with the proposed absolute configuration of 2 that was advanced by Vidari, based on an assessment of the observed Cotton effects in CD spectroscopy. In 2003, Ohta and coworkers7 reported the discovery of related neodolastanes tricholomalides A, B, and C (structures 11, 12, and 13 of Fig. 9.3) from Tricholoma sp. They concluded that the tricholomalides possessed the opposite absolute configuration claimed for the trichoaurantianolides. This conclusion was based upon the independent analysis of their circular dichroism studies. By application of the octant rule for substituent effects on cisoid a,b- unsaturated ketones,8 Ohta and coworkers suggested a revision of the prior assignment of absolute configuration for the trichoaurantianolides. This asser- tion was advanced in spite of the consistently positive specific rotations recorded in different solvents for trichoaurantianolides A, B, and C1,2 versus the negative values of tricholomalides A (11) and B (12) (compare values in Figs. 9.1 and 9.3). Note that tricholomalide C (13) only differs from trichoaurantianolide B (2) as a C-8 diastereomeric alcohol, presented in the antipodal series. The specific rotation of 13 was of little value since it was recorded as [a]0 (c 0.01, MeOH).7 In 2006, Danishefsky described a pathway for the total synthesis of racemic tricholomalides A and B, and this effort led to a revision of the relative C-2 stereochemistry (Fig. 9.3; revised structures 14 and 15).9 It seemed rather unusual that genetically similar fungi would produce closely related metabolites as enantiomers, but certainly this is not unprecedented. As a starting point, this issue lacked clarity, and we concluded that our synthesis plans must unambig- uously address the issues of absolute configuration. The chemistry of dolabellane and dolastane diterpenes has been reviewed.10 The proposed pathway for biosynthesis of the trichoaurantianolides and related compounds (Fig. 9.4) follows an established sequence from geranyl- geranyl pyrophosphate (16), which undergoes p-cation cyclization to initially form the eleven-membered ring of 17. The event is followed by a second cyclization to form the dolabellane cation 18, and this [9.3.0]cyclotetradecane skeleton is central to several families of natural products. Direct capture or elimination from 18 leads to the 3,7-dolabelladiene 19, which presents the most common pattern of unsaturation within this class. Compounds within this group are traditionally numbered beginning with C-1 as the bridgehead carbon bearing the methyl group rather than following the connectivity presented in ger- anylgeranyl 16. The cation 18 also undergoes a 1,2-hydrogen migration and elimination, which leads to a transannular cyclization yielding the 5e7e6 tri- cyclic dolastane 20. The secodolastanes, represented by 21, are a small collec- tion of marine natural products, which arise from oxidative cleavage of C10eC14 in the parent tricycle 20. In analogous fashion, the neodolabellane structure 22 is produced from 18 by stereospecific backbone migrations that result in the vicinal placement of the bridgehead methyl and isopropyl substituents. Transannular cyclizations, stemming from 22, yield the class of neodolastane diterpenes (23). Trichoaurantianolides and the related lepistal A (5) are the result of oxidations and cleavage of the C-ring (C4eC5) of 23, which leads to the features of an unusual butyrolactone system. The guanacastepenes, such as 24,11 and heptemerones, such as 25,12 are primary examples of the 5e7e6 neodolastane family, and these metabolites have also been isolated from fungi sources. A characteristic structural feature is the vicinal, syn-relationship of the bridgehead methyl and isopropyl sub- stituents as compared with the 1,3-trans relationship found in dolastanes (Fig. 9.2, structures 8 and 9). Guanacastepenes have proven to be attractive targets for synthesis studies.11,13 However, these fungal metabolites exhibit the antipodal, absolute stereochemistry as compared with neodolastanes from marine origins, such as sphaerostanol (26) (Fig. 9.5).14 

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4. Connecting the Greenland ice-core and U∕Th timescales via cosmogenic radionuclides: testing the synchroneity of Dansgaard–Oeschger events

   https://doi.org/10.5194/cp-14-1755-2018  

   Adolphi, Florian ; Bronk Ramsey, Christopher ; Erhardt, Tobias ; Edwards, R. Lawrence ; Cheng, Hai ; Turney, Chris S. ; Cooper, Alan ; Svensson, Anders ; Rasmussen, Sune O. ; Fischer, Hubertus ; et al ( January 2018 , Climate of the Past)

   Abstract. During the last glacial period Northern Hemisphere climate was characterizedby extreme and abrupt climate changes, so-called Dansgaard–Oeschger (DO)events. Most clearly observed as temperature changes in Greenland ice-corerecords, their climatic imprint was geographically widespread. However, thetemporal relation between DO events in Greenland and other regions isuncertain due to the chronological uncertainties of each archive, limitingour ability to test hypotheses of synchronous change. In contrast, theassumption of direct synchrony of climate changes forms the basis of manytimescales. Here, we use cosmogenic radionuclides (¹⁰Be,³⁶Cl, ¹⁴C) to link Greenland ice-core records toU∕Th-dated speleothems, quantify offsets between the two timescales, andimprove their absolute dating back to 45000 years ago. This approach allowsus to test the assumption that DO events occurred synchronously betweenGreenland ice-core and tropical speleothem records with unprecedentedprecision. We find that the onset of DO events occurs within synchronizationuncertainties in all investigated records. Importantly, we demonstrate thatlocal discrepancies remain in the temporal development of rapid climatechange for specific events and speleothems. These may either be related tothe location of proxy records relative to the shifting atmospheric fronts orto underestimated U∕Th dating uncertainties. Our study thus highlightsthe potential for misleading interpretations of the Earth system whenapplying the common practice of climate wiggle matching.

    

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5. A sealed‐tube method for offline δ 13 C analysis of CO 2 via a Gas Bench II continuous‐flow isotope ratio mass spectrometer

   https://doi.org/10.1002/rcm.9040  

   Walker, Brett D. ; Beaupré, Steven R. ; Griffin, Sheila ; Walker, Jennifer ; Druffel, Ellen ; Xu, Xiaomei ( February 2021 , Rapid Communications in Mass Spectrometry)

   The isotopic measurement of environmental sample CO₂via isotope ratio mass spectrometry (IRMS) can present many analytical challenges. In many offline applications, exceedingly few samples can be prepared per day. In such applications, long‐term storage (months) of sample CO₂is desirable, in order to accumulate enough samples to warrant a day of isotopic measurements. Conversely, traditional sample tube cracker systems for dual‐inlet IRMS offer a capacity for only 6–8 tubes and thus limit throughput. Here we present a simple method to alleviate these concerns using a Gas Bench II gas handling device coupled with continuous‐flow IRMS.

   Sample preparation entails the cryogenic purification and quantification of CO₂on a vacuum line. Sample CO₂splits are expanded from a known volume to several sample ports and allowed to isotopically equilibrate (homogenize). Equilibrated CO₂splits are frozen into 3 mm outer diameter Pyrex break‐seals and sealed under vacuum with a torch to a length of 5.5 cm. Sample break‐seals are scored, placed into 12 mL Labco Exetainer^®vials, purged with ultrahigh‐purity helium, cracked inside the capped helium‐flushed vials and subsequently measured via a Gas Bench equipped IRMS instrument using a CTC Analytics PAL autosampler.

   Our δ¹³C results from NIST and internal isotopic standards, measured over a time period of several years, indicate that the sealed‐tube method produces accurate δ¹³C values to a precision of ±0.1‰ for samples containing 10–35 μgC. The tube cracking technique within Exetainer vials has been optimized over a period of 10 years, resulting in decreased sample failure rates from 5–10% to <1%.

   This technique offers an alternative method for δ¹³C analyses of CO₂where offline isolation and long‐term storage are desired. The method features a much higher sample throughput than traditional dual‐inlet IRMS cracker setups at similar precision (±0.1‰).

    

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