Rocks, resolution, and the record at the terrestrial K/T boundary, eastern Montana and western North Dakota

Reconstructions of mass extinction events are based upon faunal patterns, reconstructed from numerical and diversity data ultimately derived from rocks. It follows that geological complexity must not be subsumed in the desire to establish patterns. This is exemplified at the Terrestrial Cretaceous-Tertiary (K/T) boundary in eastern Montana and western North Dakota, where there are represented all of the major indicators of the terrestrial K/T transition: dinosaurian and non-dinosaurian vertebrate faunas, pollen, a megaflora, iridium, and shocked quartz. It is the patterns of these indicators that shape ideas about the terrestrial K/T transition. In eastern Montana and western North Dakota, the K/T transition is represented lithostratigraphically by the Cretaceous Hell Creek Formation, and the Tertiary Tullock Formation. Both of these are the result of aggrading, meandering, fluvial systems, a fact that has important consequences for interpretations of fossils they contain. Direct consequences of the fluvial depositional environments are: facies are lenticular, interfingering, and laterally discontinuous; the occurrence of fossils in the Hell Creek and Tullock formations is facies-dependent; and the K/T sequence in eastern Montana and western North Dakota is incomplete, as indicated by repetitive erosional contacts and soil successions. The significance for faunal patterns of lenticular facies, facies-dependent preservation, and incompleteness is discussed. A project attempting to reconstruct vertebrate evolution in a reproducible manner in Hell Creek-type sediments must be based upon a reliable scale of correlations, given the lenticular nature of the deposits, and a recognition of the fact that disparate facies are not comparable in terms of either numbers of preserved vertebrates or depositional rates

Trans-Atlantic Correlation of Upper Cretaceous Marine Sediments

Upper Cretaceous marine deposits from the Mid-Atlantic region of North America (Delaware, Maryland, and New Jersey) and the Maastricht area (southern Netherlands, and nearby Belgium and Gennany) are correlated across the Atlantic using a variety of macro invertebrates, nannofossils, and sequence stratigraphy. Four late Cretaceous Mid-Atlantic sequences, the Marshalltown, Englishtown, Merchantville, and Navesink, span the upper Santonian to lowennost Danian, and have direct correlatives in the Maastricht area. Correlations between the Mid-Atlantic and the Maastricht regions (respectively) are as follows: the upper Santonian to lower Campanian Merchantville and Matawan formations with the Achen and lower Vaals fonnations; the middle Campanian upper Englishtown F onnation with the upper Vaals F onnation; the uppermost middle Campanian to upper Campanian Marshalltown, Wenonah, and Mount Laurel fomlations with the lower Gulpen Fonnation; the Navesink and lower Severn fonnations with the middle Gulpen Fonnation; and the New Egypt and upper Severn fonnations with the upper Gulpen and Maastricht fonnations. Additionally, deposits of the Maastricht area also provide support for several proposed subdivisions in the Marshalltown and Navesink sequences. The correlations proposed here can serve to refine the biostratigraphy oflarge marine vertebrates known from both sides of the Atlantic

Paleoenvironments of Early Theropods, Chinle Formation (Late Triassic), Petrified Forest National Park, Arizona

Three localities in the Chinle Formation (Late Triassic), Petrified Forest National Park (PEFO), Arizona, provide insights into the paleoenvironments frequented by primitive North American theropods. At the Dinosaur Wash locality, an undetermined theropod is preserved in paleosols that indicate a transition from wet to dry conditions on the floodplain. Coelophysis bauri remains from the Dinosaur Hill locality are preserved in a filled channel scour. The paleosols at this locality contain carbonate nodules intimately associated with Fe and Mn oxides, indicative of alternating alkaline/acidic conditions around roots in response to a semi-arid climate with strong seasonal precipitation. At the Dinosaur Hollow locality, Chindesaurus bryansmalli is preserved in a setting similar to those encountered at Dinosaur Hill. The paleosols exhibit vertic features, such as pseudoanticlines, and are indicative of water-deficit periods during the year. The most complete theropod remains at PEFO are predominantly preserved in distinctive blue-colored paleosol horizons showing depletion in iron and aluminum, and exhibiting features such as localized Fe concentrations and mottling. These are interpreted as A-horizons of redoximorphic paleosols developed in wet areas of the floodplain where the degree of water saturation fluctuated. Preservational conditions of PEFO theropod localities indicate they are time-averaged attritional mortality assemblages representative of contemporaneous organisms. Comparison of these localities to the well-known Ghost Ranch, New Mexico, Coelophysis quarry reinforces the idea that the quarry represents unique preservational conditions

A Model for Integrating the Public into Scientific Research

Science progresses whenever new ways of explaining natural phenomena are revealed. New ideas can only be put to use after the results and significance of research have been brought to the attention of both the scientific and lay communities. The Milwaukee Public Museum Dig-A-Dinosaur Program is a model for scientists who want to conduct research as well as engage and educate the public in their field of study. An array of rewards is derived from including amateurs as members of a research team. Such collaborations strongly increase interest in and comprehension of science as a process. Active participation in scientific investigations promotes one\u27s ability to grasp the logic employed to construct scientific knowledge. Derivative to this, people who experience research enthusiastically share what they learn with diverse audiences. Moreover, the productivity of the scientist can be significantly increased, as exemplified in an extensive paleoecological research project conducted by the authors. In retrospect, the project provided an educational experience for the volunteers that should have been formalized. It would certainly be appropriate to earn college credit based on participation and formalization would validate this learning experience

A Floral Assemblage of the Upper Cretaceous El Gallo Formation, El Rosario, Baja California, Mexico

Over the past eight months, I have collaborated with paleontologists from the Universidad Nactional Autónoma de México to formally describe plant fossils they uncovered in Baja California between their 2013 and 2016 field seasons. We report the first floral assemblage of the dinosaur-aged El Gallo Formation, Baja California, Mexico, a small (82-specimen) collection of plant fossils from fossil soils contained within the 75.84 +/- 0.05 to 74.55 +/- 0.09 million-year-old El Disecado Member of the unit. A compound fruit belonging to the genus Operculifructus, previously reported from the 3.40 to 1.08 million year younger Cerro del Pueblo Formation, Coahuila, Mexico, dominates the flora, and displays an unusual suite of characters. We identify a fruit tissue seed cap that lies within a crown defined by distal extensions of the seed coat as a derived character unique to the taxon. Because this character has not yet been demonstrated in a grossly similar fossil reproductive structure from the younger El Cien Formation, Baja California, Mexico, we maintain that the unequivocal record of Operculifructus in Baja California is presently limited to the Mesozoic, or the age of dinosaurs. We also note a lack of characters diagnostic of family- and order-level groups within the fossils, and so consider their taxonomic position uncertain within flowering plants. Likewise, resulting from sparse character data, species-level referral is not yet possible. Temporal constraints on our analysis of relationships in the taxon suggest that character states represented by the El Gallo Operculifructus are the most primitive known within it

Cornalean affinities, phylogenetic significance, and biogeographic implications of Operculifructus infructescences from the Late Cretaceous (Campanian) of Mexico

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146566/1/ajb21179.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146566/2/ajb21179_am.pd

Paleoenvironments, taphonomy, and stable isotopic content of the terrestrial, fossil-vertebrate–bearing sequence of the El Disecado Member, El Gallo Formation, Upper Cretaceous, Baja California, México

The Late Campanian (Late Cretaceous), upper part of the El Disecado Member, El Gallo Formation, Baja California, México, preserves a rich fossil assemblage of microvertebrates and macrovertebrates, silicified logs, macroscopic plant remains, and pollen that was likely deposited as the distal part of a subaerial fan. The unit was episodic and high energy, with its salient features deriving from active river channels and sheet, debris-flow deposits. Landscape stability is indicated by the presence of compound paleosol horizons, containing Fe2O3 mottling in B horizons, cutans, and calcium carbonate concretions. All of these features indicate wet/dry cyclicity in subsurface horizons, likely attributable to such cyclicity in the climate. Drainage was largely to the north and to a lesser extent, the west; however, some current flow to the south and east is preserved which, in conjunction with the proximal location of marginal marine deposits, suggest the influence of tides in this setting. The fossil vertebrates preserved in this part of the El Disecado Member are almost exclusively allochthonous, preserved as disarticulated isolated clasts in hydraulic equivalence in the braided fluvial system. A relatively diverse microvertebrate assemblage is preserved, the largest components of which are first, dinosaurs, and second, turtles. Non-tetrapod fossils are relatively uncommon, perhaps reflecting an absence of permanent standing water in this depositional setting. Here we report a high-precision U-Pb date of 74.706 + 0.028 Ma (2σ internal uncertainty), obtained from zircons in an airfall tuff. The tuff is located low within the sequence studied; therefore, most of the sedimentology and fossils reported here are slightly younger. This date, which improves upon previously published 40Ar/39Ar geochronology, ultimately allows for comparison of these El Gallo faunas and environments with coeval ones globally. Primary stable isotopic nodules associated with roots in the paleosols of the terrestrial portion of the El Disecado Member are compared with ratios from similar sources from coeval northern and eastern localities in North America. Distinctive latitudinal gradients are observed in both δ13C and δ18O, reflecting the unique southern and western, coastal geographic position of this locality. These differences are best explained by differences in the floras that populated the northern and eastern localities, relative to the southern and western floras reported here

The extinction of the dinosaurs

Non-avian dinosaurs went extinct 66 million years ago, geologically coincident with the impact of a large bolide (comet or asteroid) during an interval of massive volcanic eruptions and changes in temperature and sea level. There has long been fervent debate about how these events affected dinosaurs. We review a wealth of new data accumulated over the past two decades, provide updated and novel analyses of long-term dinosaur diversity trends during the latest Cretaceous, and discuss an emerging consensus on the extinction's tempo and causes. Little support exists for a global, long-term decline across non-avian dinosaur diversity prior to their extinction at the end of the Cretaceous. However, restructuring of latest Cretaceous dinosaur faunas in North America led to reduced diversity of large-bodied herbivores, perhaps making communities more susceptible to cascading extinctions. The abruptness of the dinosaur extinction suggests a key role for the bolide impact, although the coarseness of the fossil record makes testing the effects of Deccan volcanism difficult.15 page(s

Early Evolution of Modern Birds Structured by Global Forest Collapse at the End-Cretaceous Mass Extinction

The fossil record and recent molecular phylogenies support an extraordinary early-Cenozoic radiation of crown birds (Neornithes) after the Cretaceous-Paleogene (K-Pg) mass extinction [1–3 ]. However, questions remain regarding the mechanisms underlying the survival of the deepest lineages within crown birds across the K-Pg boundary, particularly since this global catastrophe eliminated even the closest stem-group relatives of Neornithes [4 ]. Here, ancestral state reconstructions of neornithine ecology reveal a strong bias toward taxa exhibiting predominantly non-arboreal lifestyles across the K-Pg, with multiple convergent transitions toward predominantly arboreal ecologies later in the Paleocene and Eocene. By contrast, ecomorphological inferences indicate predominantly arboreal lifestyles among enantiornithines, the most diverse and widespread Mesozoic avialans [5–7 ]. Global paleobotanical and palynological data show that the K-Pg Chicxulub impact triggered widespread destruction of forests [8, 9 ]. We suggest that ecological filtering due to the temporary loss of significant plant cover across the K-Pg boundary selected against any flying dinosaurs (Avialae [10 ]) committed to arboreal ecologies, resulting in a predominantly non-arboreal postextinction neornithine avifauna composed of totalclade Palaeognathae, Galloanserae, and terrestrial total-clade Neoaves that rapidly diversified into the broad range of avian ecologies familiar today. The explanation proposed here provides a unifying hypothesis for the K-Pg-associated mass extinction of arboreal stem birds, as well as for the post-K-Pg radiation of arboreal crown birds. It also provides a baseline hypothesis to be further refined pending the discovery of additional neornithine fossils from the Latest Cretaceous and earliest Paleogene.Also supported by:- a 50th Anniversary Prize Fellowship at the University of Bath.- a Smithsonian NMNH Deep Time Peter Buck Postdoctoral Fellowship.- NSF grants DGE-1650441 and DEB-1700786.</p