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Terrestrial evidence for the Lilliput effect across the Cretaceous-Paleogene (K-Pg) boundary
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Abstract
Recent research has demonstrated that the Lilliput effect (reduction of body size in response to a mass extinction) affected all trophic levels in the marine realm following the Cretaceous-Paleogene (K-Pg) event. However, it is unclear if this size change was strictly a marine signal, or a global phenomenon that also affected continental ecosystems. Herein we present the results of an ichnological proxy for body size of soil-dwelling insects across the K-Pg boundary in Big Bend National Park, Texas, U.S.A. Quantitative efforts focused on Naktodemasis isp., which are characterized as unbranching burrows composed of ellipsoidal packets of backfill menisci. These traces were likely produced by beetle larvae or cicada nymphs based on previous comparison with structures generated in modern soils and laboratory experiments. As an approximation for the body size of the subterranean insects, this dataset indicates that a smaller Naktodemasis diameter (DN) is statistically correlated (α < 0.05) with several edaphic factors including poor drainage and weak development (Entisols). Additionally, the DN in strata immediately superjacent to the highest Cretaceous-specific taxa is smaller by 23% (5.6 ± 1.8 mm) in comparison to DN within the subjacent Cretaceous interval (7.3 ± 2.7 mm). This abrupt shift occurs in a well-drained Inceptisol, and cannot be attributed to facies changes, drainage, or paleosol maturity. Furthermore, a reduced DN (6.6 ± 2.3 mm) persists above this anomalous shift for at least 20 stratigraphic meters within chron 29r. The cause for this negative response in body size within soil-dwelling biota may be attributed to plant-community shifts in taxonomic composition and ecological strategies, which would have caused fundamental alterations to the diet of the herbivorous, subterranean insects. This study provides empirical evidence that the Lilliput effect was not restricted to marine environments during the aftermath of the K-Pg event.
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Insects are not dinosaurs – and they probably pose us more strange ACKNOWLEDGEMENTS puzzles and unexpected questions. A million extant species, that is sev- For A. P. Rasnitsyn, preparing of various parts of this book was s- eral times more than all other living taxa together, is still a very c- ported in part by grants: by the International Science Foundation, by servative estimate, and their real number is for sure many times more. the Leverhulme Trust to D. L. J. Quicke and M. G. Fitton; by the Royal They are incomparably diverse in terms of their size, structure and way Society Joint Project with the FSU to APR and E. A. Jarzembowski; by of life – and yet they are all small – by our standard at least – why? And ESF Project ‘Fossil Insects Network’; by RFFI grants 95-04-11105, they practically ignore the cradle of life, the sea – again, why? Of 98-04-48518; by the Smithsonian Institution and California Academy course, some survive and even reproduce in salt water, but nevertheless of Sciences; and by various help, including sharing unpublished very few of them are specialised for marine life.
Beetles are the most diverse group of macroscopic organisms since the mid-Mesozoic. Much
of beetle speciosity is attributable to myriad life habits, particularly diverse-feeding strategies
involving interactions with plant substrates, such as wood. However, the life habits and early
evolution of wood-boring beetles remain shrouded in mystery from a limited fossil record.
Here we report new material from the upper Permian (Changhsingian Stage, ca. 254–252
million-years ago) of China documenting a microcosm of ecological associations involving a
polyphagan wood-borer consuming cambial and wood tissues of the conifer Ningxiaites
specialis. This earliest evidence for a component community of several trophically interacting
taxa is frozen in time by exceptional preservation. The combination of an entry tunnel
through bark, a cambium mother gallery, and up to 11 eggs placed in lateral niches—from
which emerge multi-instar larval tunnels that consume cambium, wood and bark—is ecologically
convergent with Early Cretaceous bark-beetle borings 120 million-years later.
Lamniform sharks are apex marine predators undergoing dramatic local and regional decline worldwide, with consequences for marine ecosystems that are difficult to predict. Through their long history, lamniform sharks have faced widespread extinction, and understanding those ‘natural experiments’ may help constrain predictions, placing the current crisis in evolutionary context. Here we show, using novel morphometric analyses of fossil shark teeth, that the end-Cretaceous extinction of many sharks had major ecological consequences. Post-extinction ecosystems supported lower diversity and disparity of lamniforms, and were dominated by significantly smaller sharks with slimmer, smoother and less robust teeth. Tooth shape is intimately associated with ecology, feeding and prey type, and by integrating data from extant sharks we show that latest Cretaceous sharks occupied similar niches to modern lamniforms, implying similar ecosystem structure and function. By comparison, species in the depauperate post-extinction community occupied niches most similar to those of juvenile sand tigers (Carcharias taurus). Our data show that quantitative tooth morphometrics can distinguish lamniform sharks due to dietary differences, providing critical insights into ecological consequences of past extinction episodes.
Overprinting of marine ichnofossils by morphologically similar recent continental traces is reported in unconsolidated Cretaceous‒Paleogene successions of southern New Jersey, USA. Within the glauconitic sand-dominated Hornerstown Formation, Thalassinoidesisp. burrow framework contains traces of modern burrowing bees and wasps that penetrate the outcrop up to 1 m. The modern insect traces exhibit occasional branching and are unlined. Insect burrow diameters (7‒25 mm) are within the range of Thalassinoides traces (4‒31 mm), therefore, neither size nor gross morphology can be used to distinguish between these widely diachronous, and unrelated, trace fossils. However, the presence of backfill menisci and a beige clay-rich burrow halo (suggestive of bio-irrigation) help distinguish the thalassinidean origin, whereas the highly oxidized fill and the presence of a terminal brooding chamber are diagnostic of the modern insect burrows.
ABSTRACT:Thalassinoides isp. burrow networks filled with green to dark bluish-gray glauconite pellets occur inthe Cretaceous to Paleogene Hornerstown Formation and in the uppermost 1–2 m of the underlying UpperCretaceous Navesink and New Egypt Formations at many central New Jersey Cretaceous–Paleogene (K/Pg) boundary sections. Near the base of the Hornerstown Formation is a renowned bonebed, the Main FossiliferousLayer (MFL), which contains isolated to articulated Cretaceous marine reptiles, turtles, birds, and crocodiles interpreted as a thanatocoenosis. We investigated the bulk chemical composition of the burrow fill andsurrounding matrix in the largely unconsolidated sections of the K–Pg interval at two sites, Inversand and Walnridge (Meirs) Farm, New Jersey, using a Niton XL3t XRF analyzer to place them in proper stratigraphiccontext. Bulk matrix Zr and Ti concentrations decrease up section as a result of transgression, deepening, and increased distance from source areas. In contrast, an increase in K is attributed to greater amounts and maturity of the glauconite, due to decreasing sedimentation rates. Zr and Ti concentrations in burrow fills below the MFL are virtually the same as in overlying sediments above the MFL and much less than in the surrounding matrix.This suggests that burrows in the Cretaceous strata were passively filled with Paleogene sediments. K concentrations of burrow fills are generally intermediate between the high values encountered in the Paleogene matrix and the lower values of the Cretaceous matrix. Although this may have resulted from removal ofglauconite during bioturbation and burrow filling, it is more likely that immature glauconite was sequestered inthe burrow fills below the depth of glauconitization before it could attain full maturity. Therefore, burrows originating above the formational contact at or above the MFL penetrate as much as two meters into underlying Cretaceous sediments, and are passively filled with Paleogene sediment. Burrows originating above the MFL may translocate diagnostic Danian microfossils, shocked quartz, and Ir, effectively diffusing the K–Pg boundary. This research demonstrates that care must be taken in sampling pervasively bioturbated strata to avoid incorporating stratigraphically younger burrow-fill sediments.
Degree of bioturbation, Thalassinoides isp. morphology, and diameters were compared across the Cretaceous-Paleogene (K-Pg) boundary interval at three localities along the New Jersey coastal plain. Within this regionally extensive ichnoassemblage, mean burrow diameters decrease abruptly by 26-29% (n = 1767) at the base of the Main Fossiliferous Layer (MFL) or laterally equivalent horizons. The base of the MFL has been previously interpreted as the K-Pg boundary based on the last occurrence of Cretaceous marine reptiles, birds, and ammonites, as well as iridium anomalies and associated shocked quartz. Along with the mean, the maximum and minimum burrow diameters exhibit a negative shift, which indicates that the changes are the result of a directional reduction in diameter, rather than an artifact of decreased variance. As a proxy for the size of the tracemaker, a change in burrow diameter indicates a decrease in thalassinid crustacean body size. We interpret this shift as dwarfing within the endobenthic community as detrital food sources became scarce following the mass extinction. Despite the difference in size, there is no change in framework geometry. Ichnofabric indices generally increase up-section at each site across the K-Pg chronostratigraphic boundary, indicating a regional reduction in sedimentation rate, which is supported by a gradual increase in glauconite maturity. Overall, the ichnological evidence at these localities suggests that a prolonged period of negative feedback followed a short-term positive endobenthic response across the K-Pg boundary.
Adult body size in animals is determined by the duration of the growth period and the amount of mass gained during that period. Few models of body size regulation distinguish between these two components or explicitly address the mechanisms that control the duration of the growth period. Body size in the tobacco hornworm Manduca sexia is controlled by three underlying physiological factors: growth rate; timing of the onset of juvenile hormone decay (which initiates the processes leading to pupation), as measured by the critical weight; and the timing of prothoracicotropic hormone (PTTH, which stimulates ecdysteroid secretion) and ecdysteroid secretion, as measured by the interval to cessation of growth (ICG, the time interval between the attainment of the critical weight and entry into the pre-pupal wandering stage). The critical weight and the ICG determine the duration of the growth period, while growth rate determines how much mass accumulates during that period. We studied how phenotypic plasticity of body size in M. sexia, in response to variation in temperature and diet quality, is affected by phenotypic plasticity of these three physiological determinants of body size. We show that plasticity of size in response to diet quality is regulated by variation in growth rate and critical weight, while plasticity of size in response to temperature is regulated by variation in growth rate and the ICG. These results demonstrate the importance of the timing of hormonal events in the regulation of phenotypic plasticity. We suggest that the differential sensitivity of the physiological processes that regulate body size may enable insects to adjust adult body size in response to simultaneous variation in multiple types of environmental stimuli.
Seeds of two palm species conforming to the extant genus Sabal have been recovered from the Campanian (Upper Cretaceous) Aguja Formation of Big Bend National Park, Texas: Sabal bigbendense sp. nov. and Sabal bracknellense (Chandler) Mai. These remains, found together with anatomically preserved palm stems, augment previous reports of Sabalites ungeri (Lesq.) Dorf leaves from the same formation. The co-occurrence of palm seeds with numerous juvenile hadrosaur and ceratopsian bones indicates that palms closely related to modern cabbage palms may have provided fodder and shelter for young herbivorous dinosaurs. The distribution of these and other Late Cretaceous palm fossils is reviewed.
Angiosperm woods occur throughout Upper Cretaceous (84-66 million years old) continental strata of Big Bend National Park, Texas, USA. Vertebrate remains occur along the same stratigraphic levels, providing a rare opportunity to reconstruct associations of sedimentary facies, wood remains, and vertebrate remains. The wood collection sites span a vertical stratigraphic succession that corresponds to an environmental transect from poorly-drained coastal salt- or brackish water swamps to progressively better drained freshwater flood-plains lying at increasingly greater distance from the shoreline of the inland Cretaceous sea and at higher elevations. The eight dicot wood types of the Aguja Formation differ from the five types of the Javelina Formation, paralleling a change from a fauna dominated duckbill and horned dinosaurs to a fauna dominated the large sauropod, Alamosaurus. These woods increase the known diversity of Cretaceous woods, and include the earliest example of wood with characteristics of the Malvales. The lower part of the upper shale member of the Aguja contains numerous narrow axes, some seemingly in growth position, of the platanoid/icacinoid type, and of another wood that has a suite of features considered primitive in the Baileyan sense. Duckbill dinosaur remains are common in the facies with these woods. In contrast to other Cretaceous localities with dicot wood, Paraphyllanthoxylon is not common. Dicotyledonous trees are most abundant at the top of the Aguja and the lower part of the Javelina Formations in sediments indicating well-drained inland fluvial flood-plain environments. One locality has logs and in-situ stumps, with an average spacing of 12-13 metres between each tree, and trees nearly 1 metre in diameter. To our knowledge this is the first report of anatomically preserved in situ Cretaceous dicot trees. Javelinoxylon wood occurs at all levels where remains of the giant sauropod Alamosaurus occur. The vertebrate faunas of the late Cretaceous of New Mexico and Texas are said to comprise a 'southern' fauna distinct from the 'northern fauna' of Alberta and Montana. The wood remains are consistent with such provincialism. It has been suggested that dicots were not commonly trees in the late Cretaceous of the northern part of the western interior of North America. The Big Bend woods provide direct evidence for dicot trees having more than a subordinate role in Cretaceous vegetation at lower latitudes. Most of the dicot wood types of Big Bend are characterized high proportions of parenchyma, over 50% in one type. Whether these high proportions of parenchyma are correlated with the higher CO2 levels of the Cretaceous and/or the pressures exerted aggressive browsing large dinosaur herbivores is unknown.
Cretaceous-Tertiary (KT) sequences in Nuevo Leon and Tamaulipas, Mexico, contain trace fossils that shed important light on the nature and duration of deposition of the KT boundary strata in that region. The KT clastic sequence in northeastern Mexico typically is divided into three distinct sedimentary units which represent distinctly different depositional events. Unit I is an unbioturbated, laminated deposit of alternating smectite grains and calcite spherules. Unit II is a sandstone that is mostly unbioturbated, but a few spherule-filled burrows occur near the base of the unit. Several burrows were truncated by overlying sand layers within Unit II, indicating that they were excavated following deposition of the first sand layers and then filled with spherules, scoured, and overlain by more Unit II sand. Unit III consists of alternating sandstone, siltstone, and shale that contain abundant trace fossils, including Chondrites, Ophiomorpha, Planolites, and Zoophycos. The nature of the trace fossil occurrences attest to at least three successive colonization episodes of the accreting substrate. The sandstone beds of Unit III were deposited episodically, and burrowing occurred during the period of deposition, not after deposition had ceased. The burrows were filled with late Cretaceous sediment. Trace fossil evidence indicates, therefore, that the entire KT clastic sequence must have been deposited over a long period of time. If the sperules in Unit I are material derived from an extraterrestrial impact, that impact must have predated the extinction of Cretaceous plankton by a significant time interval, which is represented by the periods of deposition of Units II and III. The ichnologic information indicates episodic deposition of Units II and III over an extended time period. Thus, the event that produced the calcite spherules in Unit I is not directly related to the Cretaceous plankton extinctions at the KT boundary, which occur at the top of Unit III.
Three new wood types from the Late Cretaceous and one from the Paleocene of Big Bend National Park, Texas, U.S.A. add to our knowledge of North Ameri-can Late Cretaceous and Paleocene plants. Sabinoxylon wicki sp. nov. provides further evidence of similarities in late Campanian-early Maastrichtian vegetation of Texas, New Mexico, and northern Mexico. This species is characterized by mostly solitary vessels, scalariform perforation plates, vessel-ray parenchyma pits similar to intervessel pits, vasicentric tracheids, and two size classes of rays. Storage tissue accounts for close to 50% of its wood volume. Another of the new Cretaceous wood types, referred to as Big Bend Ericalean Wood Type I, has more than 40 % ray parenchyma. Both Big Bend Ericalean Wood Type I and Sabinoxylon have a combination of characters that occurs in the order Ericales (sensu APGII). The third new Cretaceous wood type is from a small axis (less than 3 cm diameter), and has a combination of features that is the most common pattern in extant eudicots (vessels solitary and in radial multiples randomly arranged, simple perforation plates and alternate intervessel pits, and heterocellular rays). The Paleocene wood (cf. Cunonioxylon sensu Gottwald) differs from all other North American Paleocene woods and has characteristics found in the predominantly Southern Hemisphere family Cunoniaceae. The characteristics of these new Big Bend woods contribute to a database for fossil angiosperm woods, and allow for comparison of incidences of selected wood anatomical features in Northern Hemisphere Cretaceous woods from Albian to Maastrichtian time as well as comparison with extant woods. Cretaceous woods as a whole differ from Recent woods in having higher incidences of exclusively solitary vessels, scalariform perforation plates, and wide rays (>10-seriate), and lower incidences of ring porosity, wide vessels (> 200 µm), vessels in groups, non-random arrangements of vessels, and marginal parenchyma. The occur-rence of relatively high percentages of storage cells (> 40%) in some Cretaceous trees is noteworthy; the ability to produce wood with varying amounts and arrangements of parenchyma is likely to be a contributing factor to the success of angiosperm trees in a wide variety of environments.
Author Summary
Sixty-six million years ago the Chicxulub bolide impacted the Earth, marking the Cretaceous–Paleogene boundary (KPB). This event caused the planet's most recent mass extinction, but the selectivity and functional consequences of the extinction on terrestrial plants has been largely unknown. A key untested hypothesis has been that a subsequent impact winter would have selected against slow-growing evergreen species, a possible cause of the modern dominance of high-productivity deciduous angiosperm forests. We tested this hypothesis using fossil leaf assemblages across a 2-million-year interval spanning the KPB. We assess two key ecological strategy axes—carbon assimilation rate and carbon investment—using leaf minor vein density and leaf mass per area as proxies, respectively. We show that species that survive the KPB have fast-growth ecological strategies corresponding to high assimilation rates and low carbon investment. This finding is consistent with impact winter leading to the nonrandom loss of slow-growing evergreen species. Our study reveals a dramatic example of the effect of rapid catastrophic environmental change on biodiversity.
Forty-nine insect damage types morphologically characterize plant-insect asso-ciations spanning a 136 m composite boundary interval from the uppermost Creta-ceous Hell Creek Formation to the lowest Paleocene Fort Union Formation. The time duration of this interval is • 2.2 m.y., 1.4 m.y. of which is latest Cretaceous. These data originate from 80 localities from the Williston Basin of southwestern North Da-kota and are allocated to four assemblage zones consisting of 385 megafloral mor-photypes of bryophytes, ferns, conifers, cycads, Ginkgo, monocots, and 333 dicots. All 49 foliar damage types were produced by external foliage feeding, mining, galling, and piercing and sucking insects, each of which was assigned one of the fol-lowing host specificity levels: generalized, intermediate, or specialized. A distinctive pattern emerged when these damage types were plotted stratigraphically: of the 22 damage types that survive the Cretaceous-Tertiary boundary (K-T), 55% are gener-alized; of the 15 damage types that are extinguished immediately below the boundary, all are specialized or intermediate, as are the 12 damage types that disappear in stepped fashion somewhat before the boundary. Within this interval only two damage types are unique to the Fort Union Formation, occurring during the lowest Paleocene. These data indicate that highly and moderately specialized associations were prefer-entially culled at the K-T boundary, disproportionately enriching early Paleocene floras in generalized herbivores as dominant colonizers. These data are local, and the Signor-Lipps effect may partially obscure the true pattern, thus restricting extrapo-lation to the Western Interior of North America. Nevertheless, (1) the selective ex-tinction of specialist herbivores at the boundary, (2) the absence of significant evidence for immigrant colonization, (3) the prolonged occurrence of species-depauperate flo-ras during the Paleocene, and (4) the high percentage of last occurrences at and not before the boundary, despite the Signor-Lipps effect, suggest a role for end-Cretaceous abiotic perturbation and consequent biotic response in the evolution of modem plant and insect associations.
Changes in pollen and spore assemblages across the Cretaceous–Paleogene (K–Pg) boundary elucidate the vegetation response to a global environmental crisis triggered by an asteroid impact in Mexico 66 Ma. The Cretaceous–Paleogene boundary clay, associated with the Chicxulub asteroid impact event, constitutes a unique, global marker bed enabling comparison of the world-wide palynological signal spanning the mass extinction event. The data from both hemispheres are consistent, revealing diverse latest Cretaceous assemblages of pollen and spores that were affected by a major diversity loss as a consequence of the K–Pg event. Here we combine new results with past studies to provide an integrated global perspective of the terrestrial vegetation record across the K–Pg boundary. We further apply the K–Pg event as a template to asses the causal mechanism behind other major events in Earths history. The end-Permian, end-Triassic, and the K–Pg mass-extinctions were responses to different causal processes that resulted in essentially similar succession of decline and recovery phases, although expressed at different temporal scales. The events share a characteristic pattern of a bloom of opportunistic “crisis” tax followed by a pulse in pioneer communities, and finally a recovery in diversity including evolution of new taxa.
Based on their similar extinction and recovery patterns and the fact that the Last and First Appearance Datums associated with the extinctions are separated in time, we recommend using the K–Pg event as a model and to use relative abundance data for the stratigraphic definition of mass-extinction events and the placement of associated chronostratigraphic boundaries.
Plant and associated insect-damage diversity in the western U.S.A. decreased significantly at the Cretaceous-Paleogene (K-Pg) boundary and remained low until the late Paleocene. However, the Mexican Hat locality (ca. 65 Ma) in southeastern Montana, with a typical, low-diversity flora, uniquely exhibits high damage diversity on nearly all its host plants, when compared to all known local and regional early Paleocene sites. The same plant species show minimal damage elsewhere during the early Paleocene. We asked whether the high insect damage diversity at Mexican Hat was more likely related to the survival of Cretaceous insects from refugia or to an influx of novel Paleocene taxa. We compared damage on 1073 leaf fossils from Mexican Hat to over 9000 terminal Cretaceous leaf fossils from the Hell Creek Formation of nearby southwestern North Dakota and to over 9000 Paleocene leaf fossils from the Fort Union Formation in North Dakota, Montana, and Wyoming. We described the entire insect-feeding ichnofauna at Mexican Hat and focused our analysis on leaf mines because they are typically host-specialized and preserve a number of diagnostic morphological characters. Nine mine damage types attributable to three of the four orders of leaf-mining insects are found at Mexican Hat, six of them so far unique to the site. We found no evidence linking any of the diverse Hell Creek mines with those found at Mexican Hat, nor for the survival of any Cretaceous leaf miners over the K-Pg boundary regionally, even on well-sampled, surviving plant families. Overall, our results strongly relate the high damage diversity on the depauperate Mexican Hat flora to an influx of novel insect herbivores during the early Paleocene, possibly caused by a transient warming event and range expansion, and indicate drastic extinction rather than survivorship of Cretaceous insect taxa from refugia.
The fossil record demonstrates that past climate changes and extinctions significantly affected the diversity of insect leaf-feeding damage, implying that the richness of damage types reflects that of the unsampled damage makers, and that the two are correlated through time. However, this relationship has not been quantified for living leaf-chewing insects, whose richness and mouthpart convergence have obscured their value for understanding past and present herbivore diversity. We hypothesized that the correlation of leaf-chewing damage types (DTs) and damage maker richness is directly observable in living forests. Using canopy access cranes at two lowland tropical rainforest sites in Panamá to survey 24 host-plant species, we found significant correlations between the numbers of leaf chewing insect species collected and the numbers of DTs observed to be made by the same species in feeding experiments, strongly supporting our hypothesis. Damage type richness was largely driven by insect species that make multiple DTs. Also, the rank-order abundances of DTs recorded at the Panamá sites and across a set of latest Cretaceous to middle Eocene fossil floras were highly correlated, indicating remarkable consistency of feeding-mode distributions through time. Most fossil and modern host-plant pairs displayed high similarity indices for their leaf-chewing DTs, but informative differences and trends in fossil damage composition became apparent when endophytic damage was included. Our results greatly expand the potential of insect-mediated leaf damage for interpreting insect herbivore richness and compositional heterogeneity from fossil floras and, equally promisingly, in living forests.
An ultra-high-resolution analysis of major and trace element contents from the Cretaceous-Paleogene boundary interval in the Caravaca section, southeast Spain, reveals a quick recovery of depositional conditions after the impact event. Enrichment/depletion profiles of redox sensitive elements indicate significant geochemical anomalies just within the boundary ejecta layer, supporting an instantaneous recovery -some 10(2) years- of pre-impact conditions in terms of oxygenation. Geochemical redox proxies point to oxygen levels comparable to those at the end of the Cretaceous shortly after impact, which is further evidenced by the contemporary macrobenthic colonization of opportunistic tracemakers. Recovery of the oxygen conditions was therefore several orders shorter than traditional proposals (10(4)-10(5) years), suggesting a probable rapid recovery of deep-sea ecosystems at bottom and in intermediate waters.
The widespread mass extinctions at the end of the Cretaceous caused world-wide disruption of ecosystems, and faunal responses to the one-two punch of severe environmental perturbation and ecosystem collapse are still unclear. Here we report the discovery of in situ terrestrial fossil burrows from just above the impact-defined Cretaceous-Paleogene (K/Pg) boundary in southwestern North Dakota. The crisscrossing networks of horizontal burrows occur at the interface of a lignitic coal and silty sandstone, and reveal intense faunal activity within centimeters of the boundary clay. Estimated rates of sedimentation and coal formation suggest that the burrows were made less than ten thousand years after the end-Cretaceous impact. The burrow characteristics are most consistent with burrows of extant earthworms. Moreover, the burrowing and detritivorous habits of these annelids fit models that predict the trophic and sheltering lifestyles of terrestrial animals that survived the K/Pg extinction event. In turn, such detritus-eaters would have played a critical role in supporting secondary consumers. Thus, some of the carnivorous vertebrates that radiated after the K/Pg extinction may owe their evolutionary success to thriving populations of earthworms.
This study documents the traces and burrowing behaviors of nymphs of the prairie cicada Cicadetta calliope (Hemiptera: Cicadidae), as observed in neoichnological experiments. Cicada nymphs were col- lected from the C horizons of sandy Fluvents along the Kansas River east of Lawrence, Kansas. The nymphs appeared to be fifth instars, 13-17 mm long and 6-7 mm wide. Nymphs were placed in plastic enclosures containing layers of colored, moist, very fine-grained sand. They burrowed immediately, excavating air-filled, sediment-enclosed cells between 20 mm and 40 mm long and averaging 9 mm wide. Burrowing was completed in three stages: (1) sediment in the forward portion of the cell was excavated and rolled into a ball with the fore- limbs; (2) the nymph turned 180 using a forward roll, and moved to the back of the cell; and (3) the sediment ball was pushed up against the back wall of the cell and kneaded with the forelimbs into a thin layer. Resulting burrow traces are sinuous and distinctly me- niscate and demonstrate that insect larvae construct meniscate, back- filled burrows in well-drained terrestrial settings. Cicadetta calliope nymphs and their traces are excellent analogs for meniscate trace fossils commonly found in late Paleozoic-Cenozoic alluvial deposits and paleosols. Such meniscate trace fossils are useful for interpreting the paleoenvironment and paleohydrogeology of the units in which they are found. In addition, such backfilled burrows can be used to supplement the fossil record of cicada-like hemipterans, currently known only from the latest Permian to the Early Triassic.
Ichnology is the science that studies traces, mostly trace fossils, which are defined as morphologically recurrent structures (nests, burrows, trackways) resulting from the life activity of an individual organism modifying the substrate. Leonardo da Vinci was probably the first ichnologist. He mentioned the existence of traces of worms in rocks. Trace fossils reflect how extinct animals behaved. They are as parts of a time machine that allow us to almost see how extinct animals made their nests, fed, reproduced and walked. Moreover, they allow us to reconstruct palaeoenvironments and the evolutionary history of many taxa. Ichnology was originally developed by geologists; traces first caught our attention in rocks (palaeoichnology) and then in extant environments (neoichnology). For many years ichnology was only studied in marine or lacustrine environments, whereas terrestrial ichnology has been developed over the last few decades. Insect traces are the most common in terrestrial environments, such as palaeosols, but they are also common in plant remains, bones, and in some subaquatic substrates. Ichnoentomology deals with insect traces in soils, palaeosols and other substrates.
We analyzed samples for paleomagnetism, ⁴⁰Ar/³⁹Ar detrital sanidine ages, and mammalian fauna to produce a precise chronostratigraphic framework for the Upper Cretaceous to Lower Paleocene Dawson Creek section of Big Bend National Park, west Texas. Prior to this work, the absolute ages and durations of the Upper Cretaceous Aguja and Javelina Formations and Paleocene Black Peaks Formation were relatively poorly constrained. The documented polarity zones can be correlated to C32n-C31n, C29r, and C27r of the geomagnetic polarity time scale, with three hiatuses spanning more than 1.5 m.y. each. Rock magnetic analyses indicate that the dominant magnetic carrier in the Aguja and Black Peaks Formations is titanomagnetite, while the Javelina Formation has varying magnetic carriers, including hematite, magnetite, and maghemite. An overprint interval surrounding the Cretaceous-Paleogene boundary suggests the primary magnetic carrier, titanohematite, was likely reset by burial and/or overlying basaltic flows. These are the first independent age constraints for the Cretaceous-Paleocene strata at the Dawson Creek section that determine the age and duration of deposition of each formation in the section, as well as the age and duration of multiple unconformities through the succession. As a result, these age constraints can be used to reassess biostratigraphic and isotopic correlations between the Big Bend area and other Cretaceous-Paleogene basins across North America. Based on this new data set, we reassign the age of the mammalian fauna found in the Black Peaks Formation from the Puercan to the Torrejonian North American Land Mammal age. Our age constraints show that the dinosaur fauna in the Javelina Formation in the Dawson Creek area is latest Maastrichtian and restricted to chron C29r. Thus, the Javelina dinosaur fauna is correlative to the Hell Creek Formation dinosaur fauna from the Northern Great Plains, indicating differences between the faunas are not due to differences in age, and providing support for the hypothesis of provinciality and endemism in dinosaur communities in the late Maastrichtian. Further, the age constraints indicate that the previously documented mid-Maastrichtian and late Maastrichtian greenhouse events were rapid ( < 200 k.y.) and correlate closely with climate events documented in the marine record.
Significance
A mass extinction occurred at the Cretaceous−Paleogene boundary coincident with the impact of a 10-km asteroid in the Yucatán peninsula. A worldwide layer of soot found at the boundary is consistent with global fires. Using a modern climate model, we explore the effects of this soot and find that it causes near-total darkness that shuts down photosynthesis, produces severe cooling at the surface and in the oceans, and leads to moistening and warming of the stratosphere that drives extreme ozone destruction. These conditions last for several years, would have caused a collapse of the global food chain, and would have contributed to the extinction of species that survived the immediate effects of the asteroid impact.
The Early Toarcian (Early Jurassic) global marine mass extinction is associated with one of the most important environmental perturbations of the Mesozoic, the Toarcian Oceanic Anoxic Event (T-OAE), usually interpreted as a global oceanic anoxic event. In the Lusitanian Basin (LB) — one of the reference areas for the study of the T-OAE — despite an elevated extinction rate among marine invertebrates, the anoxia hypothesis has been discarded based on geochemical and isotopic data. In the Fonte Coberta section the T-OAE is characterised by the extinction of the previously well-represented brachiopod taxa, a decreased abundance of ammonoids, and the establishment of a well-developed endobenthic community mainly composed by Thalassinoides tracemaker, which indicates favourable environmental parameters at least for this community. Thus, the palaeoenvironmental changes associated with the T-OAE event bear a minor incidence on the macrobenthic tracemaker community at the level of extinctions and changes in diversity or abundance; yet they exert a major effect on the behaviour and palaeobiology of tracemakers. The Thalassinoides specimens show an exclusively horizontal development and unusual architectural features during the extinction interval, tied to behavioural adaptations to nutrient availability and/or substrate firmness. Smaller burrow diameters are registered at the base of the T-OAE, and then an increase is observed during the T-OAE. This could be associated with a palaeobiological response (Lilliput effect) to palaeoecological changes at the beginning of the T-OAE, followed by a progressive change to pre-event environmental parameters. This study therefore sheds light on how environmental alterations can determine specific behavioural and palaeobiology changes of the producer, as reflected by variations in significant features of Thalassinoides architecture.
In Plants and the K-T Boundary, two of the world's leading experts in palynology and paleobotany provide a comprehensive account of the fate of land plants during the ‘great extinction’ about 65 million years ago. They describe how the time boundary between the Cretaceous and Paleogene Periods (the K-T boundary) is recognized in the geological record, and how fossil plants can be used to understand global events of that time. There are case studies from over 100 localities around the world, including North America, China, Russia and New Zealand. The book concludes with an evaluation of possible causes of the K-T boundary event and its effects on floras of the past and present. This book is written for researchers and students in paleontology, botany, geology and Earth history, and everyone who has been following the course of the extinction debate and the K-T boundary paradigm shift.
The Agost section (Betic Cordillera, Alicante Province, south-eastern Spain) is one of only a few places in the world where complete sedimentary successions across the Cretaceous–Palaeogene (K–Pg) boundary are available. Agost enables a high-resolution ichnological analysis illustrating the influence of environmental perturbations on burrowing organisms before, during and after the K–Pg boundary event. The uppermost Maastrichtian calcareous marlstones and marly limestones of the Raspay Formation (Plummerita hantkeninoides Biozone), beside the light-filled Maastrichtian trace fossils, contain dark-coloured early Danian trace fossils including Chondrites targionii, Chondrites ?affinis, Chondrites isp., Pilichnus isp., Planolites isp., ?Teichichnus isp., Thalassinoides isp., Trichichnus linearis, Trichichnus isp., and Zoophycos isp. The ichnotaxonomic composition of the late Maastrichtian and early Danian trace fossil association does not reveal major differences, indicating no significant influence on composition of their trace makers immediately after the K–Pg event. The main factors that most likely promoted survivorship of the trace makers were their feeding strategy (deposit feeders, microbe gardeners) and an increased delivery of organic matter to the seafloor due to the high mortality during the K–Pg boundary event. However, the differences in the size of trace fossils are noted: They are distinctly smaller in the dark boundary layer (Guembelitria cretacea Biozone) than in the underlying uppermost Maastrichtian calcareous marlstones. This is an example of the Lilliput Effect. The dwarfed ichnoassociation was produced during and shortly after sedimentation of the dark boundary layer pointing to a delayed reaction of the burrowing organisms to the K–Pg boundary event compared to other groups of organisms. The dwarfing might be caused by environmental stress resulting from lower food supply due to collapse of primary production in the later phases of the K–Pg boundary event.
The New Jersey Inner Coastal Plain is underlain by a Campanian (Upper Cretaceous) to Thanetian (Paleocene) stratigraphic sequence containing fossil assemblages from before, during and after the K/T boundary mass extinction event. The lithostratigraphic framework and the microfossil zonation of these faunal changes is reviewed. Microstratigraphic analysis of the sequence reveals that dominant marine organisms of the Upper Cretaceous such as ammonites and oysters are selectively extirpated at the K/T boundary, while those organisms with a non-planktotrophic reproductive strategy were the surviving marine invertebrates. Comparative taphonomy is applied to two fossil assemblages in the sequence to demonstrate the differences between reworked taphocoenoses of nearshore and estuarine environments and those of deeper-water taphocoenoses. A complete synonymy for all New Jersey K/T vertebrate taxa is presented, and all valid taxa are plotted on a stratigraphic range chart with guild/niche information about each group. Two geochemical investigations are evaluated for their bearing on the question of catastrophic extinction processes caused by asteroid impact. It is concluded that the methodology of comparative taphonomy can be a useful tool in determining the difference between transported, reworked fossil assemblages produced by physical events like storms, and those assemblages which accumulated in deeper-water settings where modification was primarily biological. The mass extinction event as recorded in this sequence was gradual, but exacerbated by a sharper mass mortality at the end of the Cretaceous; diversity rebound to pre-K/T levels did not occur until the Thanetian. Plankton crash most drastically affected those organisms with a planktotrophic larval stage. The drop in plankton biomass was mediated upward in the food chain to duraphagous predators (and to those who ate them) by way of the die-off in previously abundant Cretaceous mollusks. The iridiuim data are ambiguous, and toxic metal data lend no support to the Strangelove Ocean hypothesis. Finally, it would appear that a combination of gradual climatic changes coupled with a sudden event like a bolide impact caused a protracted period of mass extinctions with suppression of full biomass productivity lasting well into the Paleocene.
Trace fossil analysis of the Cretaceous-Paleogene (K/Pg) boundary interval at El Kef (Tunisia) has provided new information on the response of the macrobenthic tracemaker community to the K/Pg boundary event. Ichnological data from the Global Stratotype Section and Point (GSSP) for the Cretaceous-Paleogene (K/Pg) boundary were completed with those from a new, well-exposed section nearby. The trace fossil assemblage consists of dominant Trichichnus, frequent Chondrites, and rare Thalassinoides and Zoophycos in the uppermost Maastrichtian, and only Trichichnus in the lowest Danian, the diversity being comparatively lower than in other K/Pg boundary sections worldwide. Bioturbational structures are observed continuously across the K/Pg boundary interval, without primary lamination; this discards anoxic conditions. However, the upward-decreasing diversity in the sections may be related to a transition from a moderately dysoxic or slightly dysoxic macrobenthic habitat in the sediment during the latest Maastrichtian to a strong or very strong dysoxia during early Danian. Comparison with micropaleontological data reveals a minor influence of the K/Pg boundary event on the macrobenthic tracemaker community, while the change in oxygenation of pore waters at the El Kef sections can be attributed to local or regional phenomenon, marked by increasing clay content in the Danian sediments.
Lower Permian (Asselian) deposits of the Washington Formation (Dunkard Group) in West Virginia (U.S.A.) represent proximal to distal expressions of a migrating, anastomosing river and associated floodplain environments. These deposits are part of the upper fluvial plain province of the Dunkard Basin characterized by thick-to-thin sandstone bodies, shales, and paleosols. The paleosols and associated ichnofossils record a wealth of paleoenvironmental, paleoecological, and paleoclimatic data which improve our understanding of the autogenic and allogenic processes that result in the spatial and temporal variability of ancient fluvial systems. This study integrates field and laboratory analysis of paleosols and ichnofossils including macro- to micromorphology, bulk geochemistry, and clay mineralogy to better understand variations in soil-forming processes across this Early Permian floodplain. Nine different pedotypes were identified including proximal, poorly developed Entisols and Inceptisols, poorly drained Histosols, and thick, moderately to well-drained Inceptisols and Vertisols. Lateral differences in paleosol properties were minor compared to the diversity of paleosols present in the vertical exposure and were largely a result of localized variations in drainage and topography. Differences in the properties of the paleosols in the vertical succession could not be explained by variable drainage due to position on the floodplain. Cyclicity was largely controlled by avulsion, but was overprinted by changes in climate. While climatic drying during the Early Permian as a general trend is well established, smaller scale fluctuations between wet and dry intervals contributed significantly to observed paleosol properties. Dominance by calcareous Vertisols in the upper fluvial plain facies province and their representation of strongly seasonal conditions are consistent with previous research; however, thorough investigation of the paleosols suggests that more humid conditions existed than the arid to semiarid climate that has been suggested.
The influence of substrate firmness as shear strength on the nesting behavior of the wasp Bembix oculata is analyzed in "natural" conditions. The experimental area (a landing pit at the athletics stadium in Granada, southern Spain), is characterized by the existence of a non-random distribution of nesting holes made by Bembix oculata. The analysis of sediment features shows homogeneity in some substrate properties such as grain size and mineralogy. However, the quantitative analysis of substrate firmness leads to recognition of a close relationship between shear-strength values and burrow distribution. Experiments performed by Torvane testing in 13 sampling sites reveal changes in shear strength related to variations in water content of the substrate. These changes in shear strength are closely associated with distribution of nests. Thus, a gradual increase in substrate shear strength, over 1000-1500 Pa, is recorded toward the area where nesting holes appear, whereas burrows are most abundant where shear strength is higher (above 2500 Pa). Substrate firmness is revealed to be of prime importance in the nesting behavior of Bembix oculata. The relationship between the obtained shear-strength values and the soil water content could be interpreted as the influence of water content in substrate firmness. However, we do not discard the influence of water content as an independent factor (soil moisture).
Analysis of molluscan collections from a 3+my interval around the Cretaceous-Tertiary (K-T) interval in east Texas suggests that molluscs suffered an extinction at or near the K-T boundary, followed by a prolonged period of stress which lasted through the P0 and P1a planktic foraminiferal zones. Species richness and the relative abundance of deposit feeders generally track the 13C depletion curve suggesting that the stress was caused by a lack of primary production. A stable, relatively diverse, suspension feeding molluscan community was reestablished less than two million years after the K-T boundary. -from Authors
Geochemical and isotopic analyses of the Cretaceous–Paleogene (K/Pg) boundary deposits were conducted at the Caravaca section (External Subbetic, southeast of Spain) in order to evaluate the recovery of the macrobenthic tracemaker community and the bioturbational disturbance. Samples from the infilling material of several lower Danian dark-colored trace fossils (Chondrites, Planolites, Thalassinoides and Zoophycos) located in the uppermost 8-cm of the light upper Maastrichtian strata, as well as samples from the host sedimentary rock of these trace fossils, were analyzed and compared with data from the lower Danian deposits. The values of element ratios indicative of extraterrestrial contamination (Cr/Al, Co/Al and Ni/Al) are higher in the infilling trace fossil material than in the upper Maastrichtian and lower Danian deposits, which suggests a contribution of the ejecta layer. Regarding the isotope composition, the δ13C values are lower in the infilling material than in the Maastrichtian host sedimentary rocks surrounding the traces, while the δ18O are higher in the infilling material. The geochemical and isotopic compositions of the infilling material evidence the unconsolidated character of the sediment, including the red boundary layer. Softground conditions confirm a relatively rapid recovery by the macrobenthic tracemaker community, starting a few millimeters above the K/Pg boundary layer. The mixture of the infilling material of the trace fossils moreover reveals a significant macrobenthic tracemaker activity affecting K–Pg boundary transition sediments that may have significantly altered original signatures.
Two types of root casts attached to in situ stump casts of early trees from the Catskill Delta Complex are described and contrasted. The first type is attached to bulbous sand-stone tree-stump casts (Eospermatoperis sp. ?) occurring in a low-chroma (gray-green), pyritic, gley siltstone paleosol of Middle Devonian (Givetian) age that is interpreted as waterlogged; this paleosol formed in a coastal-margin setting characterized by a shallow water-table. Root casts in the Middle Devonian paleosol are horizontal to subhorizontal, strap-like (measuring 0.5-2 cm in width and up to meters long), and radiate outward from stump casts with distinctly flared bases. Root casts with a similar morphology also occur attached to the upper portions of stump casts, and comprised an aerial root mantle. The second type of root cast is attached to weakly flared to corm-like sandstone tree-stump casts of probable progymnosperms (Archaeopteris sp. ?) occurring in a moderate-chroma (red), oxidized sandy paleosol of Late Devonian (Famennian) age that is interpreted as well-drained; this paleosol formed proximal to active alluvial channels. Root casts are dominantly vertical, taproot-like (measuring up to 10-15 cm in diameter and up to 1.5m long), and descend downward from the bases of stump casts with approximately a 60° angle of attachment. The two types of tree-root casts differ due to development under different soil-drainage conditions. Preservation of in situ Devonian tree-stump casts and attached root casts involved degradation of interior tissues, followed by sediment infilling; outer tissue (periderm) persisted longer before decay and infilling. Preservation is favored by conditions of rapid sediment accumulation, generally associated with sandstone deposition, as is the case for Carboniferous lycopod tree stumps documented by other workers. Lack of preservation in fine-grained claystone paleosols associated with either coastal-margin mudflat or alluvial floodplain deposition reflects either (1) no colonization of these soil environments by mature trees, (2) selective destruction of the root traces by intensive physical mixing associated with vertic (shrink-swell) soil processes in clay paleosols, or (3) average sediment accumulation rates that were too low to bury and preserve in situ stump casts.
The purpose of this chapter is to evoke new concepts, provide guidelines and new frontiers for future research, and demonstrate that invertebrate traces actually comprise the “backbone” of continental (as well as marine) ichnology. Invertebrate organisms that inhabit the continental, nonmarine realm include some of the most diverse and populous classes in the animal kingdom. For example, both the Insecta and Crustacea exhibit burrowing behaviors unique to subaqueous freshwater and subaerial systems. Because of the sheer biomass of burrowing pupae, larvae, juvenile, and adult stages of these organisms, invertebrates dependent on the position of the water table form the basis for ecological niche-partitioning of depositional systems within all of the continental realm. A distinction must be made here between continental and marine ichnocoenoses because they represent distinctly different styles of living. These in turn dictate different behavioral and genetic responses of the organisms that inhabit them. Burrow architectures that occur in both continental and marine ichnocoenoses can be differentiated by subtle differences in morphology that are due to convergence of the burrowing mechanisms of the respective organisms.
The first Cicadomorpha, Gallodunstania grauvogeli gen. et sp. nov., is described from the Triassic of the Vosges (France) and is provisionally attributed to the Palaeontinoidea family Dunstaniidae.
Paleosol properties are routinely characterized by whole-rock geochemistry, compromising the interpretation of important biogeochemicalinformation in deep time. As a consequence, we employ a new pedotransfer function approach to the characterization of paleosols and apply this methodology to Late Cretaceous (Campanian and Maastrichtian) and early Paleocene (Danian) landscapes from the Dawson Creek study area of the western interior to: (1) reconstruct collodially based physical and chemical soil properties, and (2) assess climate and soil biogeochemical controls on evolving terrestrial ecosystems. Nine paleoseries (i.e., pedotypes) characterize the range of soil properties within the fluvial stratigraphic succession, which includes Entisols, Inceptisols, and Vertisols. All soils had optimal water-holding potential as inferred from low bulk densities, whereas poorly drained and colonizing landscapes likely suffered from poor aeration during seasonal water logging. Even with high water-holding capacity, Maastrichtian soils experienced seasonal moisture stress because of lower rainfall than Campanian and Danian soils. Fertility levels were sufficient for the growth of most plants judging from high cation exchange capacity and base saturation, negligible aluminum toxicities because of nonacid pH, and limited salinity and sodicity from relatively low exchangeable sodium and soluble salts in solution. Unlike warm-temperate and forested paleosols with neutral pH from the Campanian and Danian, subtropical and alkaline paleosols from the Maastrichtian apparently supported a woodland plant formation adapted to low availability of iron and manganese, which were fixed with calcium in carbonate, and low availability of phosphorous because it formed insoluble compounds with iron and manganese. Carbon, nitrogen, phosphorous, and sulfur cycling through microbially mediated mineralization of soil organic matter was limited from low litter inputs in both early and midsuccessional ecosystems, particularly in woodland soils. Results do not revealdemonstrable changes in soil characteristics through the K-T transition.
The Clayton sands, thin discontinuous sand bodies found at or near the
Cretaceous-Tertiary (K-T) boundary at various sites in Alabama,
previously have been attributed to (1) catastrophic tsunami deposition
associated with a K-T boundary impact or, alternatively, (2)
noncatastrophic transgressive infilling of incised valleys cut during a
preceding sea-level low-stand. New observations on the geometry and
ichnosedimentologic character of a Clayton sand body, enveloping strata,
and associated bounding surfaces exposed along Mussel Creek (central
Alabama) refute the tsunami origin and support the latter mechanism.
Studies of other boundary deposits in the gulf region, which may
similarly benefit from ichnofossil investigations, should consider more
rigorously the evidence for sea-level change near the K-T transition.
The marine to terrestrial transition in the Big Bend area falls within the Late Cretaceous Aguja Formation, and the Cretaceous-Tertiary boundary falls within the Javelina Formation. No record of a catastrophic event is apparent in the Javelina Formation. The Javelina, Black Peaks, and Hannold Hill Formations and the Big Yellow Sandstone Member of the Canoe Formation record increasing uplift in the region. Volcanism in the Chisos Mountains is the source of upper Canoe Formation sediments. The sequence of changes produced by this trend is gradual and the Javelina through Black Peaks units are not lithostratigraphically distinct at the formation level. The Aguja Formation and the Tornillo Formation are united in the Chilicotal Group (new), which spans the deposits from the first significant influxes of terrestrial sediments, formed as the Cretaceous sea retreated, up to the beginning of local volcanism in the Chisos. The volcanic strata of the upper Canoe Formation are reassigned to the Chisos Formation.-from Authors
A marked change in paleosols coincides with the Cretaceous/Tertiary transition in fluvial sediments of the Big Bend region in Texas. Early Paleocene paleosols exhibit thick, black epipedons and a greater depth to the argillic and petrocalcic horizons compared to Late Cretaceous paleosols. These features and comparison with modern soils suggest that early Paleocene soils developed under conditions of higher rainfall and cooler temperatures than did Late Cretaceous soils. The change in paleosols occurs abruptly at the highest occurrence of dinosaur bones in the section.
Paleosol-bearing alluvial strata of latest Cretaceous and earliest Tertiary age are continuously exposed along Dawson Creek, in Big Bend National Park, west Texas, U.S.A., and exhibit a three-tier hierarchy of depositional cyclicity. Meter-scale, fluvial aggradational cycles (FACs) occur as fining-upward successions that are gradation-ally overlain by paleosols or are sharply overlain by the coarser-grained base of the succeeding FAC without an intervening paleosol. FACs stack into decameter-scale, fluvial aggradational cycle sets (FAC sets) that also fine upward, and from base to top contain either a grad-ual upsection increase in soil maturity and soil drainage or a somewhat symmetrical pattern of increasing and decreasing paleosol maturity. Longer-period trends of FAC thickness, lithologic proportions, paleosol maturity, and paleosol drainage indicate that two complete, and two partial, hectometer-scale fluvial sequences occur within the study in-terval. From base to top, each sequence is characterized by an asym-metric increase and decrease in FAC thickness, a decrease in the pro-portion of sand-prone fluvial facies, an increase in paleosol maturity, and better paleosol drainage. Whereas FACs and FAC sets are interpreted to record cyclic epi-sodes of channel avulsion and stability, and longer-term avulsive chan-nel drift within the alluvial valley, respectively, fluvial sequences may coincide with third-order sea-level changes within the North American Western Interior Seaway. As such, the Cretaceous–Tertiary (K–T) transition within the Tornillo Basin may provide an example of me-gascale stratigraphic cyclicity that is controlled by eustatic sea level within a fully fluvial succession. Thickening and thinning successions of FACs record a third-order period of accelerating (transgressive-equivalent) and decelerating (highstand-equivalent) base-level rise, and subsequent base-level fall (falling stage-to lowstand-equivalent). Se-quence boundaries are placed at the sharp inflection between thinning and thickening FACs. Sand-prone facies and immature, more poorly-drained paleosols are associated with the transgressive-equivalent por-tion of each sequence, and mudrock-dominated overbank facies and their associated mature, well-drained paleosols are associated with the highstand-and falling stage-equivalent.