杏吧原创

Moore et al. 2026. The ontogenetically youngest known pachycephalosaur (Dinosauria: Ornithischia) postcranium. Journal of Vertebrate Paleontology. Article: e2616325, 19 p. 听

Pachycephalosaurian dinosaurs are represented in the fossil record primarily by their taphonomically resistant frontoparietal domes, that developed fully only at maturity. Consequently, the postcranial record of Pachycephalosauria is poor, particularly for immature forms. Here, we describe the ontogenetically youngest known, and Canada鈥檚 second-most complete, pachycephalosaur postcranium, collected from the uppermost Maastrichtian Frenchman Formation, Saskatchewan. Despite its small size (estimated total length ~ 90 cm), the skeleton shows several characters diagnostic of Pachycephalosauria, including a double ridge and groove articulation on the pre- and postzygapophyses of the dorsal neural arches, a medial flange on the postacetabular process of the ilium, and a highly reduced pubis that contributes only minimally to the acetabular margin. Histological sectioning of the crural bones shows an immature woven bone texture. The absence of cyclical or annual growth indicators suggests that this specimen was less than a year old at the time of death. Phylogenetic analysis recovers the specimen as a member of Pachycephalosaurinae, perhaps related to Prenocephale, but the lack of cranial data for our specimen and the complementary lack of postcranial data for other pachycephalosaurs make this determination tenuous. Spatiotemporal considerations suggest a possible but currently untestable affiliation with Sphaerotholus buchholtzae. The relatively long hindlimbs of the juvenile compared to those of adult pachycephalosaurs indicate probable negative ontogenetic allometry in the hindlimbs..

Hatton et al. 2025. Assessing the Impacts of Land-Use Change and Climate Variability on Cyanobacterial Abundance and Toxicity in Shallow Lakes. Freshwater听Biology.听v. 70 (7) Article e70066, 19 p. DOI: https://doi.org/10.1111/fwb.70066

1. The global increase in the frequency and intensity of cyanobacteria blooms has been widely attributed to changes in land-use practices and climate variability, yet little is known of how toxicity has varied historically relative to cyanobacteria abundance.

2. Fossil pigments from cyanobacteria and algae were quantified from shallow lake sediment core records using high-performance liquid chromatography, whilst past concentrations of microcystin congeners were measured using liquid chromatography high-resolution mass spectrometry. These metrics were combined with measures of sedimentary geochemistry (未13C, 未15N, %N, %C, C:N ratio) to estimate how lake production and abundance of toxigenic cyanobacteria varied during the past ~300 years in two small lakes in New Brunswick, Canada. Harvey Lake is an impacted site with a history of intensive catchment land use, whilst Wheaton Lake is a relatively undisturbed reference site.

3. Stratigraphically constrained cluster analysis (CONISS) revealed that primary production increased steadily in both lakes since the second half of the 20th century, whilst microcystin production increased by an order of magnitude after ca. 2000 CE. Fossil pigment concentrations were initially lower in Harvey Lake but shifted to more productive conditions after initial forest clearance and settlement and again after agricultural intensification during the 20th century. Although Wheaton Lake exhibited higher overall fossil pigment concentrations, including a pre-colonial eutrophic interval (ca. 1680鈥�1750 CE), this reference basin also underwent enrichment since ca. 1980, possibly reflecting longer growing seasons in the last 50 years.

4. Although cyanobacterial pigments and microcystin concentrations were elevated in sediments deposited since ca. 2000 CE in both lakes, these variables were uncorrelated over the entire 300-year record, with the pre-colonial eutrophic interval in Wheaton Lake having low toxin concentrations. This pattern suggests either that cyanobacterial dominance and toxicity are regulated by different factors or that the preservation of microcystins and pigments is under unique controls.

McCarthy, et al. 2025.听High-resolution analysis of the varved succession at Crawford Lake across the base of the proposed Crawfordian Stage and Anthropocene Series.听 Anthropocene Review.听v. 12(2) 243-272. DOI https://doi-org.proxy.library.carleton.ca/10.1177/20530196251315454

Four years after the Anthropocene Working Group (AWG) voted to work toward defining the Anthropocene series/epoch with a base in the mid-20th C, the varved sediments of Crawford Lake (Milton, ON, Canada) were selected as the Global boundary Stratotype Section and Point (GSSP) candidate. The initial major rise in activity of 239鈥�+鈥�240Pu had been selected as the primary chronostratigraphic marker to define the base of the Anthropocene, but the precise year when this occurred could not be determined from measurements of samples combining multiple varves. Individual varves from freeze cores collected in April 2023 provide annual resolution for bomb radionuclides, allowing the varve age model to be refined, former assignments determined to have been 1鈥墆ear too old. The increase in 239鈥�+鈥�240Pu activities (calculated from atom concentrations of 239Pu and 240Pu measured using Accelerated Mass Spectrometry) of 0.0031鈥塀q/g between varves now assigned to 1951 and 1952 is consistent with the onset of thermonuclear weapons testing on November 1, 1952, so the proposed base for the Anthropocene is at the contact between the light- and dark-coloured laminae deposited in 1952 CE (17.5鈥塩m in core CRA23-BC-1F-B). Sharply lower 239鈥�+鈥�240Pu and 137Cs activities capture the moratorium from November 1958 to September 1961 before rising quickly to peak activities of 239鈥�+鈥�240Pu in 1963 CE. Analysis of individual varves with varying amounts of organic matter and inorganic calcite illustrates the influence of lithology on organic proxies, but the upcore trend toward depleted values of 未15N through the 20th C reflects increased fossil fuel combustion worldwide. An inflection point in 未15N around 1911 CE is attributed the global impact of the Haber-Bosch process and establishment of nearby steel mills, and another in the early 1950s attributed to the Great Acceleration to which the tipping point in the Earth system is attributed.

Spence et al. 2025.听Process synchrony a key control of resilience in a subarctic freshwater systems. Earth’s Future. 2024EF005518R

Climate鈥恑nduced changes in streamflow and biogeochemistry are occurring across the northern circumpolar region but several key unknowns include (a) the mechanisms responsible among landscapes and permafrost conditions, (b) the resilience and precariousness of hydrological and biogeochemical regimes. Even though it is among the largest physio鈥恈limatic regions of the northern circumpolar, these knowledge gaps are acute in the Taiga Shield. This research aimed to determine if hydrology and biogeochemistry regimes of the Taiga Shield have been resilient to recent climate warming. We apply a recently developed framework of hydrological resilience that shows the first 20 years of the 21st century were the warmest and wettest of the previous 300 years. These conditions altered the catchment such that >50% of the water year streamflow now occurs during winter, shifting the catchment from a nival to a cold season pluvial hydrological regime. This regime shift has significantly changed the fraction of inorganic nitrogen export, but insufficiently to shift the biogeochemical regime. Sustained multi鈥恲ear physical process synchronization was the cause of these changes. This behavior is not well simulated by existing Earth system models. The tipping point in local mean annual air temperatures was crossed near the turn of the century well below the warming threshold of the Paris Accord. A one鈥恠ize鈥恌its鈥恆ll approach to mitigation targets is not effective at preventing all shifts in Earth systems. This is important to consider as regime changes in small hydrological systems have the potential to trigger cascading effects in the larger catchments to which they contribute.

Walsh et al. 2025. Late 20th Century Hypereutrophication of Northern Alberta鈥檚 Utikuma Lake. Environments. 12, 63. https://doi.org/10.3390/environments12020063

Eutrophication in Canadian lakes degrades water quality, disrupts ecosystems, and poses health risks due to potential development of harmful algal blooms. It also economically impacts the general public, industries like recreational and commercial fishing, and tourism. Analysis of a 140-year core record from Utikuma Lake, northern Alberta, revealed the processes behind the lake鈥檚 current hypereutrophic conditions. Endmember modeling analysis (EMMA) of the sediment grain size data identified catchment runoff linked to specific sedimentological processes. ITRAX X-ray fluorescence (XRF) elements/ratios were analyzed to assess changes in precipitation, weathering, and catchment runoff and to document changes in lake productivity over time. Five end members (EMs) were identified and linked to five distinct erosional and sedimentary processes, including moderate and severe precipitation events, warm and cool spring freshet, and anthropogenic catchment disturbances. Cluster analysis of EMMA and XRF data identified five distinct depositional periods from the late 19th century to the present, distinguished by characteristic rates of productivity, rainfall, weathering, and runoff linked to natural and anthropogenic drivers. The most significant transition in the record occurred in 1996, marked by an abrupt increase in both biological productivity and catchment runoff, leading to the hypereutrophic conditions that persist to the present. This limnological shift was primarily triggered by a sudden discharge from a decommissioned sewage treatment lagoon into the lake. Spectral and wavelet analysis confirmed the influence of the Arctic Oscillation, El Ni帽o Southern Oscillation, North Atlantic Oscillation, and Pacific Decadal Oscillation on runoff processes in Utikuma Lake鈥檚 catchment.

Keywords:

eutrophication; end member modeling analysis; ITRAX-XRF; paleolimnology; time series analysis

Galloway, et al. 2024. Organic matter is a predominant control on total mercury concentration of near-surface lake sediments across a boreal to low Arctic tundra transect in northern Canada. Science of the Total Environment. 954. 176466.

Mercury (Hg) is a bioavailable and toxic element with concentrations that are persistently high or rising in some Arctic and subarctic lakes despite reduced atmospheric emissions in North America. This is due to rising Hg emissions to the atmosphere outside of North America, enhanced sequestration of Hg to sediments by climate-mediated increases in primary production, and ongoing release of Hg from terrestrial reservoirs. To evaluate the influence of organic matter and other parameters on Hg accumulation in northern lakes, near-surface sediments were sampled from 60 lakes across a boreal to shrub tundra gradient in the central Northwest Territories, Canada. The organic matter of the lake sediments, assessed using programmed pyrolysis and petrology, is composed of a mixture of terrestrial, aquatic, and inert organic matter. The proportion of algal-derived organic matter is higher in sediments of lakes below treeline relative to shrub tundra sites. Total sedimentary Hg concentration is correlated to all organic matter constituents but is unrelated to latitude or lake position below or above treeline. The concentrations of Ag, Ca, P, S, U, Ti, Y, Cd, and Zn are also strong predictors of total sedimentary Hg concentration, indicating input from a common geogenic source and/or common sequestration pathways associated with organic matter. Catchment area is a strong negative predictor of total sedimentary Hg concentration, particularly in lakes above treeline, possibly due to retention capacity of Hg and other elements in local sinks. This research highlights the complexity of controls on Hg sequestration in sediment and shows that while organic matter is a strong predictor of total sedimentary Hg concentration on a landscape scale and across extreme gradients in climate and associated vegetation and permafrost, other factors such as catchment area and sources from mineralized bedrock are also important.

Walsh et al. 2024. Two millennial-scale paleolimnological records from San Salvador Island, Bahamas. Dryad. https://doi.org/10.5061/dryad.jm63xsjkw

Paleolimnological data from Moon Rock Pond (MRP) and Crescent Pond (CP) on San Salvador Island, Bahamas. This data was derived from analysis of gravity cores retrieved from each pond using UWITEC core barrels (core MRP20-01, 39.6 cm long; core CP20-01, 45.6 cm long) and 4.5 cm-diameter Glew-style core barrels (core MRP20-02, 41.0 cm; core CP20-02, 48.5 cm). Grain size and End Member Modelling Analysis (EMMA) were carried out on cores MRP20-01 and CP20-01, revealing six and four robust end members, respectively. X-ray fluorescence (XRF) analysis was performed on cores MRP20-02 and CP20-02 using the Itrax core scanner. Radiocarbon dating of the cores MRP20-01 and CP20-01 indicated that the cores span several thousand years (Moon Rock Pond, ~3,100 years; Crescent Pond, ~3,900 years). Together, these datasets archive records of environmental change in the Bahamas during the late Holocene.

Warnock-Juteau, et al. 2024. Computed tomographic investigation of a hatchling skull reveals ontogenetic changes in the dentition and occlusal surface morphology of Hadrosauridae (Dinosauria: Ornithischia). Vertebrate Anatomy Morphology Palaeontology 11: 111-150. DOI 10.18435/vamp29395

CMN 8917 is a partial skull that represents one of the few nestling-sized juvenile hadrosaurines known to date. Support for its placement within Hadrosaurinae includes a narial vestibule not enclosed within the premaxillary dorsal and lateral processes, the presence of an anterodorsal maxillary process, and a maxillary dorsal process that is longer anteroposteriorly than dorsoventrally. The skull also possesses tooth traits traditionally associated with lambeosaurines; secondary ridges on some maxillary and dentary tooth crowns, and denticulation on some maxillary crowns. The occurrence of these features in a juvenile hadrosaurine suggests that they are modified during ontogeny, calling into question their taxonomic utility for identifying juvenile specimens. The dentary teeth of CMN 8917 are similar to those of many adult hadrosaurids in that they possess a concave occlusal surface with steeper lingual and shallower buccal wear zones. This differs from the occlusal surface morphology present in some other juvenile hadrosaurids, which suggests interspecific differences in dental battery development鈥攑ossibly reflective of dietary differences鈥攐ccurred during early ontogeny in some taxa.

Milani, et al. 2024.听 Numerical icing simulations of heated cylinder and comparisons to flight test results. Journal of Aircraft. https://doi.org/10.2514/1.C037682

This study investigates the capabilities of ANSYS FENSAP-ICE in the context of ice protection system (IPS) development by simulating ice accretion on a heated cylinder probe mounted under the wing of the Convair-580 research aircraft. Simulations were performed using experimental data collected during a flight in natural Appendix O icing conditions and ice shapes were verified using high-resolution video of the ice accretion. No combination of simulation settings, input parameters, and multi-shot methods tested in this study generated the same macroscopic surface features observed in the experiment, however, the amount of ice accretion, general location of ice features, and formation processes were validated. These findings reveal the difficulty of simulating a short icing period (10-minutes) with a dynamic icing intensity, low LWC level, and high static air temperature. Preliminary analysis shows that users should include the vapor pressure model when simulating glaze ice and consider using more than one set of input parameters to capture the effect of changing icing intensity when simulating a highly dynamic icing environment. Simulations that include leading-edge heat flux predicted runback icing on the probe which is valuable information when developing an IPS.

Llew-Williams, et al. 2024. Quantifying conditions required for varve formation in meromictic Crawford Lake, Ontario, Canada: important process for delimiting the Anthropocene epoch. Journal of Paleolimnology 71: 101-124.

Varved sediments in meromictic Crawford Lake consist of dark-light couplets of organic matter (primarily phytoplankton and amorphous organic matter) capped by calcite crystals. The crystals precipitate in the alkaline epilimnion between spring and fall turnover, consistent with Langelier Saturation Index calculations that predict calcite precipitation when pH and temperature exceed 7.76 and ~15掳C, respectively. Climate, primary production, and the pH of the epilimnion control lamina thickness: acid rain primarily affects the precipitation and accumulation of calcite crystals, whereas both endogenic calcite and authigenic organic matter are affected by climate and primary production. Thin varves, often with barely perceptible light-coloured calcite laminae were deposited between the late 1940s and mid-1970s, when the pH of the epilimnion fell slightly in response to deterioration in air and water quality associated with rapid industrialization. Conditions required for precipitation of calcite laminae were absent during the 16^th to mid-19^th centuries, an interval corresponding to the Little Ice Age when no human impact affected the catchment. Varves dating from 1867 CE onwards (the Canadian Zone) facilitate the candidacy of the deep basin sediments of Crawford Lake to define the Anthropocene epoch.

Gonz谩lez-Migu茅ns, et al. 2023. A needle in a haystack: a new metabarcoding approach to survey diversity at the species level of Arcellinida (Amoebozoa: Tubulinea).听 Molecular Ecology Resources. DOI: 10.1111/1755-0998.13771

Environmental DNA-based diversity studies have increased in popularity with the development of high throughput sequencing technologies. This permits the potential simultaneous retrieval of vast amounts of molecular data from many different organisms and species, thus contributing to a wide range of biological disciplines. Environmental DNA protocols designed for protists often focused on the highly conserved听 small subunit of the ribosome gene that does not permit species-level assignments. Consequently, the biological information associated species is lost, and the classification of the molecular diversity into Operational Taxonomic Units cannot be compared directly between studies. To solve this issue, specific eDNA protocols based on fast evolving genes applicable to the species level have been proposed. However this approach is not yet applied routinely to protist diversity, with the exception of marine and shallow lotic freshwater ecosystems. In this study, we present a species-level eDNA protocol, designed to explore diversity of Arcellinida (Amoebozoa: Tubulinea) testate amoebae taxa, that is based on mitochondrial cytochrome oxidase subunit I (COI). These organisms are widespread in lentic water bodies and soil ecosystems. We applied this protocol to 42 samples from peatlands, estuaries and soil environments, recovering all the infraorders in Glutinoconcha except for Hyalospheniformes. With this protocol we expect to revolutionize the design of modern distributional Arcellinida surveys. Through an approach that involves rapid analysis, is cost effective and permits reliable handling of vast sampling designs, Arcellinida have to potential to be established as a model group for an array of theoretical and applied studies

Lafond, et al. 2023. Influence of climatic trends and cycles on annual varve deposition in Crawford Lake, Ontario, Canada. Geosciences 13 (3), 87, 24 p.

Varves accumulating below the chemocline of meromictic Crawford Lake, Milton, Ontario, Canada, are comprised of dark-colored organic matter laminations that are primarily deposited during the fall plankton die-off, alternating with light-colored laminations comprised of calcite crystals that are precipitated during a relatively narrow water temperature and pH-controlled depositional window in the summer. A novel high-resolution imaging protocol was used to photograph the varve record in freeze core CRA19-2FT-B2, collected from the deepest part (~23 m) of the lake in February 2019. High-resolution images were used to: 1) characterize varve couplets deposited between AD 1870 and 2000 (chronology verified through 137Cs/210Pb analysis of freeze core CRA22-1FRA-3, and consistent with the historic record of nuclear fallout and other proxies of the Great Acceleration); 2) document distinctive varves that permit correlation between cores throughout the 20 deep basin of Crawford Lake; 3) measure the thickness of individual dark and light colored laminations, which were found to vary between 0.05 mm and 3.35 mm, with a mean annual thickness 1.25 mm; and 4) carry out wavelet and spectral time series analysis based on varve thickness data that can be correlated to climatic trends and cycles. Time series analysis identified cycles with statistically significant periodicities that were attributed to the Quasi-biennial Oscillation (2.3 years), El Ni帽o Southern Oscillation (2-7 years), the 11-year Schwabe Sunspot cycle and a possible Pacific Decadal Oscillation (50-70 years). This research not only provides baseline chronostratigraphic data that allows correlation between freeze cores subsampled for various proxies, but also documents the dynamics of the climate drivers that have influenced deposition of both organic matter and inorganically precipitated calcite. Crawford Lake is currently a candidate site under consideration for the Global boundary Stratotype Section and Point (GSSP) to define the Anthropocene series/epoch.

Marshall, et al. 2023. Annual-scale assessment of mid-20th century anthropogenic impacts on the algal ecology of Crawford Lake, Ontario, Canada. PeerJ, 11:e14847, 22 p.

Meromictic Crawford Lake, located in SW Ontario, Canada is characterized by varved sediments, making it suitable for high-resolution paleoecological studies. Freeze cores, the only coring method available that reliably preserves the fragile laminations representative of summer and winter deposition in the lake, were used to document siliceous diatom and chrysophyte community structure at an annual resolution from 1930-1990CE. Stratigraphically constrained cluster analysis showed major assemblage changes that are believed to have been caused by local, regional and global anthropogenic impacts. The assemblage changes within the siliceous algae are attributed to increased industrial emissions and related effects of acid deposition on the lake鈥檚 catchment associated with the Great Acceleration the massive economic, industrial, and demographic expansion beginning in the mid-20th century which is also coincident with observed increases in spheroidal carbonaceous particles (SCPs) found within the lake sediment. The findings reported here reflect major changes in earth systems that the Anthropocene Working Group proposes to use to establish a mid-20th base for the Anthropocene Epoch, providing support for the laminated sedimentary sequence from Crawford Lake as a potential Anthropocene GSSP.

McCarthy, et al. 2023. The varved succession of Crawford Lake, Milton, Ontario, Canada as a candidate Global Boundary Stratotype Section and Point for the Anthropocene Series/ Epoch” The Anthropocene Review, 10 (1): 146-176. DOI:10.1177/20530196221149281

An annually laminated succession in Crawford Lake, Ontario, Canada is proposed as the Global boundary Stratotype Section and Point (GSSP) for the Anthropocene Series/ Epoch with听 base at 1952 CE. Sediments are composed of varve couplets of organic matter capped by calcite precipitated each summer in alkaline surface waters and included diverse proxies that reflect environmental change at global to local scales marking the start of the Anthropocene. Spheroidal carbonaceous particles and bulk sediment nitrogen isotopes record a sharp increase in fossil fuel combustion in the early 1950s, and coincide with increasing fallout from thermonuclear testing.听 Ratios of 239Pu:240Pu and 14C:12C both peak in the 1960s, the latter more than compensating for the effects of old carbon in the dolomitic basin of Crawford Lake. Rapid industrial expansion in the North American Great Lakes region led to enhanced leaching of terrigenous elements by acid precipitation during the Great Acceleration. Reduced calcite precipitation coeval and low primary production produced thin calcitic laminae around the GSSP, an event that was also marked by a sharp decline in elm pollen. The absence of fossil pigments from obligately anaerobic purple sulfur bacteria supports an oxygenated monimolimnion, while elevated bottom-water salinities preserve varve structure. This aerobic depositional environment is unusual for a meromictic lake and prevents the mobilization of 239Pu, the proposed primary stratigraphic guide for the Anthropocene.