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Paleogeographic reconstruction of the North American continent in the late Campanian illustrating the areal expanse of the Western Interior Seaway separating the Laramidia and Appalachia landmasses, after Blakey³³. Our study locations are marked by stars. Potential centers of coeval arc volcanism are also indicated. Source map © 2022 Colorado Plateau Geosystems Inc.
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The spectacular fossil fauna and flora preserved in the Upper Cretaceous terrestrial strata of North America’s Western Interior Basin record an exceptional peak in the diversification of fossil vertebrates in the Campanian, which has been termed the ‘zenith of dinosaur diversity’. The wide latitudinal distribution of rocks and fossils that represen...
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... The ashes were ejected from volcanoes in the Elkhorn Mountains of southwestern Montana and deposited across freshwater lakes and rivers including Montana's UMRBNM and the stratotype of the Judith River Formation. 9 Additional isotope data from Ramezani et al. (2022) provided ages for relevant sections in Alberta, Mexico, Montana and Utah [54], including the earliest recorded occurrences of A. simplex, P. heterotrycha and the genus Azollopsis shown in Figure 6. ]. ...
... The ashes were ejected from volcanoes in the Elkhorn Mountains of southwestern Montana and deposited across freshwater lakes and rivers including Montana's UMRBNM and the stratotype of the Judith River Formation. 9 Additional isotope data from Ramezani et al. (2022) provided ages for relevant sections in Alberta, Mexico, Montana and Utah [54], including the earliest recorded occurrences of A. simplex, P. heterotrycha and the genus Azollopsis shown in Figure 6. ]. ...
Azolla is the only plant with a co-evolving nitrogen-fixing (diazotrophic) cyanobacterial symbiont (cyanobiont), Nostoc azollae, resulting from Whole Genome Duplication (WGD) 80 million years ago in Azolla’s ancestor. Additional genes from the WGD resulted in genetic, biochemical and morphological changes in the plant that enabled transmission of the cyanobiont to successive generations via its megaspores. The resulting permanent symbiosis and co-evolution led to loss, downregulation or conversion of non-essential genes to pseudogenes in the cyanobiont, changing it from a free-living organism to an obligate symbiont. Upregulation of other genes in the cyanobiont increased its atmospheric dinitrogen fixation and provision of nitrogen-based products to the plant. As a result, Azolla can double its biomass in less than two days free-floating on fresh water and sequester large amounts of atmospheric CO2, giving it the potential to mitigate anthropogenic climate change through Carbon Capture and Storage. Azolla’s biomass can also provide local, low-cost food, biofertiliser, feed and biofuel that are urgently needed as our population increases by a billion every twelve years. This paper integrates data from biology, genetics, geology and paleontology to identify the location, timing and mechanism for the acquisition of a co-evolving diazotrophic cyanobiont by Azolla’s ancestor in the Late Cretaceous (Campanian) of North America.
... comm. to JCM, 12 July, 2023), and would have dated to approximately 76.4 Ma (Ramezani et al., 2022). Sternberg (1955) identified the specimen as a juvenile hadrosaurine, potentially related to Gryposaurus, though he refrained from assigning it to a specific genus. ...
CMN 8917 is a small, partial skull of a duck-billed dinosaur from the upper Campanian Dinosaur Park Formation in what is now Dinosaur Provincial Park, Alberta. It represents one of the few nestling-sized juvenile hadrosaurines known to date. Support for this phylogenetic placement 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, such as secondary ridges on some maxillary and dentary tooth crowns, and denticulation on some maxillary tooth crowns. The occurrence of these features in a juvenile hadrosaurine suggests that they were 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—possibly reflective of dietary differences—occurred during early ontogeny in some taxa.
... Possibly, even younger-but not yet sampled-zircons exist in the population, making the youngest measured date too old. Another popular approach is to calculate a weighted mean age from the youngest analyses that satisfy the acceptable limits of MSWD value (Augland et al., 2019;Eberth and Kamo, 2020;Ramezani et al., 2022;Sahy et al., 2017;Fig. 3A); the same caveats discussed in Section 6.3.1. ...
U-Pb geochronology by isotope dilution−thermal ionization mass spectrometry (ID-TIMS) has the potential to be the most precise and accurate of the deep time chronometers, especially when applied to high-U minerals such as zircon. Continued analytical improvements have made this technique capable of regularly achieving better than 0.1% precision and accuracy of dates from commonly occurring high-U minerals across a wide range of geological ages and settings. To help maximize the long-term utility of published results, we present and discuss some recommendations for reporting ID-TIMS U-Pb geochronological data and associated metadata in accordance with accepted principles of data management. Further, given that the accuracy of reported ages typically depends on the interpretation applied to a set of individual dates, we discuss strategies for data interpretation. We anticipate that this paper will serve as an instructive guide for geologists who are publishing ID-TIMS U-Pb data, for laboratories generating the data, the wider geoscience community who use such data, and also editors of journals who wish to be informed about community standards. Combined, our recommendations should increase the utility, veracity, versatility, and “half-life” of ID-TIMS U-Pb geochronological data.
... Until now, aspects of this complex architecture have been documented within limited stratigraphic intervals and geographic areas, creating a piecemeal understanding of the wedge, and leaving a "big picture" understanding of the wedge and its formations largely unrealized. This is unfortunate because the BRG is a significant source of Campanian-age oil, gas, and coal resources as well as dinosaur and other vertebrate fossils in the Western Interior Basin (WIB) of North America [6,[9][10][11][12]. Accordingly, accurate lithoand chronostratigraphic correlation within the BRG at numerous widely separated localities across the southern Alberta plains and beyond Alberta depends on a clear understanding of how the group's formational geometries relate to one another as well as to the units that bound the wedge (Pakowki/Lea Park and Bearpaw formations). ...
... The Foremost Fm is a coaly, marine-to-paralic unit that prograded eastward and marked the retreat from Alberta of marine environments (Pakowki/Lea Park Fm) from~80-78 Ma [8]. The Oldman Fm is a predominantly nonmarine alluvial unit that records the maximum retreat of the WIS from Alberta and western Saskatchewan at~78-77 Ma [1,7,11,12]. It thickens considerably in southwestern Alberta where it replaces the Dinosaur Park Fm and becomes younger up-section. ...
... As the Oldman Fm loses distinction to the north (~Twp 40), the Foremost and Dinosaur Park formations amalgamate, but are difficult to differentiate. The Dinosaur Park Fm is a marine-paralic and nonmarine alluvial unit that records the transgression of the Bearpaw Sea across western Saskatchewan and southern Alberta from~77-74 Ma [1,7,9,11,12,14]. It pinches out stratigraphically to the southwest in the Lethbridge area and thins toward the southeast (Manyberries area) where it extends into northern Montana. ...
The Upper Cretaceous (Campanian) Belly River Group (BRG) of southern Alberta has a complex internal stratigraphic architecture derived from differential geometries of its component formations that resulted from regionalized tectonic influences and shifting source areas. A full understanding of BRG architecture has been compromised heretofore by a limited understanding of subsurface data in southwestern- and southeastern-most Alberta. In this study outcrop exposures throughout southern Alberta are tied to reference well logs and subsurface cross-sections allowing a more precise understanding of BRG architecture and how it relates to well-known vertebrate fossil producing areas. Modifications to an existing stratigraphic model of the BRG show that the Oldman and the Dinosaur Park formations have reciprocal north-to-south wedge-shaped geometries and a diachronous contact that become prominently expressed south of Twp 12. The updated model also demonstrates that the Oldman Formation thickens stratigraphically up-section to the south, and that the Foremost-Oldman contact is, essentially, a datum across much of southern Alberta. Identification of the Oldman Formation in the subsurface remains based on its relatively high gamma-ray response in mudstone successions, but it is also recognized that many of its sandstones exhibit relatively low gamma-ray responses like those in underlying and overlying formations. Nomenclature and subdivisions of the Oldman Formation are revised to accommodate this updated understanding, and modifications are also made to the definition of the Judith River-Belly River discontinuity, a newly recognized surface that marks the onset of accommodation and eustatic rise in sea-level in the northern Western Interior Basin at ~76.3 Ma.
... The specimen was found at the base of a light gray, trough cross-stratified sandstone in the upper "muddy interval" of the Dinosaur Park Formation (88), approximately 7 m below the stratigraphically lowest coal bed of the Lethbridge Coal Zone. As such, the specimen is stratigraphically bracketed by the "Plateau Tuff" and "LCZ" bentonites that have been radiometrically-dated at 75.639 ± 0.025 Ma and 75.017 ± 0.020 Ma, respectively (89). Following the Bayesian model median age-stratigraphic model for the Dinosaur Park Formation derived by Ramenazi et al. (89) in their figure 4, the strata containing TMP 2009.12.14 are estimated to be ~75.3 million years old. ...
... As such, the specimen is stratigraphically bracketed by the "Plateau Tuff" and "LCZ" bentonites that have been radiometrically-dated at 75.639 ± 0.025 Ma and 75.017 ± 0.020 Ma, respectively (89). Following the Bayesian model median age-stratigraphic model for the Dinosaur Park Formation derived by Ramenazi et al. (89) in their figure 4, the strata containing TMP 2009.12.14 are estimated to be ~75.3 million years old. ...
Tyrannosaurids were large carnivorous dinosaurs that underwent major changes in skull robusticity and body proportions as they grew, suggesting that they occupied different ecological niches during their life span. Although adults commonly fed on dinosaurian megaherbivores, the diet of juvenile tyrannosaurids is largely unknown. Here, we describe a remarkable specimen of a juvenile Gorgosaurus libratus that preserves the articulated hindlimbs of two yearling caenagnathid dinosaurs inside its abdominal cavity. The prey were selectively dismembered and consumed in two separate feeding events. This predator-prey association provides direct evidence of an ontogenetic dietary shift in tyrannosaurids. Juvenile individuals may have hunted small and young dinosaurs until they reached a size when, to satisfy energy requirements, they transitioned to feeding on dinosaurian megaherbivores. Tyrannosaurids occupied both mesopredator and apex predator roles during their life span, a factor that may have been key to their evolutionary success.
... A subset of the grains from samples ES1772-8 and ES1772-52 analyzed using LASS were selected for chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) analyses at the MIT Isotope Laboratory, following the procedures outlined in Ramezani et al. (2022). ...
... S1). While recent chronostratigraphic work Ramezani et al., 2022) places the Oldman-Dinosaur Park formation boundary at 76.7e76.3 Ma (thus the loweremiddle portion would be younger still), the locality of BDM 107 is noted as being atypical in its stratigraphy (Warshaw and Fowler, 2022) and so the assumption that these recent ages can be used to better place the BDM 107 locality stratigraphically is potentially erroneous. ...
... Therefore, it is also possible that peripatric speciation may have played a role in generating the specific diversity seen within Daspletosaurus, with cladogenesis producing two lineages while one remains in morphological stasis relative to its sister lineage. However, since peripatric speciation requires a degree of cladogenesis, this also argues against a hypothesis of anagenesis Ramezani et al. (2022) and Rogers et al. (2023). The range of D. wilsoni is derived from Warshaw and Fowler (2022). ...
... Table 1 summarizes 73 radioisotopic age determinations from bentonitic ash beds deposited primarily in marine sediment sequences (available as an excel spreadsheet in Table S2 of the Supplementary Materials). It is beyond the scope of our effort to include and review the expansive set of age determinations from continental sediments deposited along the margins of the Western Interior Seaway that are used to evaluate the tempo of terrestrial vertebrate evolution (e.g., Ramezani et al., 2022). Table 2 are reported in the results section below. ...
Improvements in analytical procedures in parallel with intercalibration of ⁴⁰ Ar/ ³⁹ Ar and U-Pb methods and laboratories, spurred since 2003 by the EarthTime geochronology community initiative, have led to ± 2s uncertainties on the order of 50 to 100 ka, or better for Cretaceous ash beds. Assembled here are fifty-seven ⁴⁰ Ar/ ³⁹ Ar ages and sixteen ²³⁸ U- ²⁰⁶ Pb ages of volcanic ash beds in strata of the Western Interior Basin of North America determined during the last 15 years since these improvements have been made. These age determinations span from 108 Ma in the middle Albian to 66 Ma in the latest Maastrichtian. Five of the ⁴⁰ Ar/ ³⁹ Ar ages from Campanian and Maastrichtian strata are newly reported here, whereas the remainder are from the literature. Building on the pioneering work of John Obradovich and Bill Cobban, where possible these age determinations are tied to ammonite and inoceramid biostratigraphy. For most ash beds the temporal uncertainties, unlike earlier time scales for the Western Interior Basin, are much shorter than the duration of fossil biozones. Proposed ages for stage boundaries based on this review of the radioisotopic ages include: Maastrichtian-Danian 66.02 ± 0.08 Ma
Campanian-Maastrichtian 72.20 ± 0.20 Ma
Santonian-Campanian 84.19 ± 0.38 Ma
Coniacian-Santonian 86.49 ± 0.44 Ma
Turonian-Coniacian 89.75 ± 0.38 Ma
Cenomanian-Turonian 93.95 ± 0.05 Ma
Albian-Cenomanian 100.00 ± 0.40 Ma
Five bentonites that occur within the Vascoceras diartianum, Prionocylus macombi, Scaphites preventricosus, Scaphites depressus , and Desmoscaphites bassleri ammonite zones, dated using both ⁴⁰ Ar/ ³⁹ Ar and U-Pb methods, yield ages in agreement to within 150 ka and form the backbone of the Western Interior Basin time scale. In parallel, improvements in the taxonomy of ammonites, inoceramids, and foraminifera, and recent field work, is better establishing the biostratigraphic framework for these age determinations. These efforts each contribute to the progressive refinement of the chronostratigraphic framework of the Western Interior Basin, and enhance its utility for global correlation.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.6895395
... U-Pb, trace element and Hf isotope analyses of zircons at the UCSB used laser ablation ICP-MS methods following procedures described in Nelson and Cottle (2017). Zircon U-Pb geochronology by CA-(chemical abrasion) ID-TIMS was done at the Massachusetts Institute of Technology Isotope Laboratory following procedures described in Ramezani et al. (2022). Zircon O-isotope analysis at the Universität Heidelberg and zircon Lu-Hf isotope analysis at Curtin University were undertaken by secondary ion mass spectrometry and multi-collector LA-ICP-MS respectively, according to procedures documented in Turnbull et al. (2021). ...
New rock dredge samples supply key information to establish the tectonic and geological framework of the northern two‐thirds of the 95% submerged Zealandia continent. The R/V Investigator voyage IN2016T01 to the Fairway Ridge, Coral Sea, obtained poorly sorted poly‐lithologic pebbly to cobbly sandstones, well sorted fine grained sandstones, mudstones, bioclastic limestones, and basaltic lavas. Post‐cruise analytical work comprised petrography, whole rock geochemical and Sr and Nd isotopic analyses, and U‐Pb zircon, Rb‐Sr, and Ar‐Ar geochronology. A Fairway Ridge cobbly sandstone has a ∼95 Ma (early Late Cretaceous) depositional age; two biotite granite cobbles are 111 ± 1 and 128 ± 1 Ma in age, and some volcanic pebbles are also likely Early Cretaceous. Fairway Ridge basalts have intraplate alkaline chemistry and are of Late Eocene age (∼40–36 Ma). By analogy with South Zealandia, we interpret strong positive continental magnetic anomalies of North Zealandia to mainly result from Late Cretaceous to Cenozoic intraplate basalts, many of them rift‐related lavas. A new basement geological map of North Zealandia shows the position of the Mesozoic Gondwana magmatic arc axis (Median Batholith) and other major geological units. This study completes onland and offshore reconnaissance geological mapping of the entire 5 Mkm² Zealandia continent.
... For each sample, five concordant zircon grains identified by LA-ICP-MS were dislodged from the grain mounts and analysed by the CA-ID-TIMS method at the MIT Isotope Laboratory, following the procedures outlined by Ramezani et al. (2022). Selected zircon grains were annealed at 900°C for 60 h in a muffle furnace, followed by partial dissolution in purified 29M HF at 210°C for 12 h inside a high-pressure vessel, using methods modified after Mattinson (2005). ...
Intramountain late Carboniferous–Permian basins of western Europe developed during the latest orogenic stages of the Variscan Mountain Belt in eastern Pangaea, at equatorial palaeolatitudes. Their stratigraphic framework is mainly based on continental subdivisions (e.g. Stephanian and Autunian continental stages), which can be contentious due to biostratigraphic biases, resulting in long-distance diachronous subdivisions. To provide precise inter-basinal and global correlations to the internationally recognized chronostratigraphic marine stages, this study reports new U–Pb geochronology from the Aumance and Decize–La Machine basins, located in the northern French Massif Central. Zircon grains extracted from three volcanic ash-fall layers give weighted mean ²⁰⁶ Pb/ ²³⁸ U ages of 299.11 ± 0.35 Ma; 298.73 ± 0.36 Ma and 298.59 ± 0.35 Ma (2σ total propagated uncertainty) by the chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) method, coinciding with the Carboniferous–Permian transition (Gzhelian and Asselian stages). These ages imply that the northern Massif Central basins developed synchronously in relatively short periods of time (<10 Myr), reflecting substantial sedimentation rates. Finally, the new chronology of infilling of these basins confirms that they were connected during the late Carboniferous and early Permian periods, improving the knowledge on the late-orogenic Variscan geodynamic setting in this area.
Supplementary material: https://doi.org/10.6084/m9.figshare.c.6805228
