End Of The Cretaceous Research Articles

Phylogenetics and the Cenozoic radiation of lampreys

The development of a movable jaw is one of the most important transitions in the evolutionary history of animals.1 Jawed vertebrates rapidly diversified after appearing approximately 470 million years ago. Today, only lampreys and hagfishes represent the once dominant jawless grade2,3,4 and comprise less than 1% of living vertebrate species. Their relationship to other vertebrates ranks among the more contentious problems in animal phylogenetics.5,6,7,8,9,10,11,12 Further, the phylogenetic relationships within lampreys and hagfishes remain unclear,13,14,15 and the ages of their living lineages are largely unexplored.16,17 Because of their importance for the genomic and developmental changes that prefigured jawed vertebrate diversity,18,19,20,21 the evolutionary history of lampreys and hagfishes is a major frontier of organismal biology. Of these two clades, lampreys22 are more ecologically diverse, exhibiting freshwater, anadromous, and fully marine forms, as well as parasitic and nonparasitic species.23,24 Here, we present a new phylogeny and historical biogeographic reconstruction of all living lampreys. Whereas the early diversification of this clade tracks Pangaean fragmentation, lampreys also rapidly radiated in the northern hemisphere during the mid-Cretaceous and directly after the Cretaceous-Paleogene extinction. These radiations mirrored concurrent ones in other animals and plants and coincided with changes to lamprey ecology and feeding behavior. Our results suggest that 80% of living lamprey clades appeared in the last 20 million years of Earth history. Rather than gradually accumulating since the oldest stem-group forms appeared in the early Paleozoic, living lamprey biodiversity results from diversifications extending from the Cretaceous to present.

Dinosaur extinctions related to the Jenkyns Event (early Toarcian, Jurassic)

The early Toarcian Jenkyns Event (~183 Ma) was characterized by a perturbation of the global carbon cycle, global warming, which at continental areas led to intensified chemical weathering, enhanced soils erosion, and intensified wildfires. Warming and acid rain affected diversity and composition of land plant assemblages, caused a loss of forests and thereby impacted on trophic webs. The Jenkyns Event, triggered by volcanic activity of the Karoo-Ferrar Large Igneous Province, changed terrestrial ecosystems, and also affected the dinosaurs. Fossil macroplant assemblages and palynological data reveal reductions in the diversity and richness of plant communities. A substantial loss of land plant biomass and a shift to forests dominated by Cheiropelidiaceae conifers occurred as a consequence of seasonally dry and warm conditions. Major changes occurred to hervivore dinosaurs, with extinction of diverse basal families of Sauropodomorpha (‘prosauropods’) as well as some basal sauropods. Ornithischian dinosaurs show patchy records; some heterodontosaurids disappeared and the scelidosaurids (Thyreophora) went extinct during the Jenkyns Event. The dominant carnivorous dinosaurs, the Coelophysoidea (Theropoda), died out during the Jenkyns Event. We interpret the Jenkyns Event as a terrestrial crisis for ecosystems, marked especially by floral changes and the extinction of some dinosaur clades, both hervivores and carnivores.

New records of Theropoda from a Late Cretaceous (Campanian-Maastrichtian) locality in the Magallanes-Austral Basin, Patagonia, and insights into end Cretaceous theropod diversity

The end Cretaceous mass extinction was marked by a dramatic change in biodiversity, and the extinction of all non-avian dinosaurs. To understand the diversity of dinosaur clades prior to this event, as well as recovery by avian dinosaurs (birds), we need a better understanding of the global fossil record. However, the fossil record from southern localities, particularly southernmost (>60°S) South America, has only recently begun to be described. Discoveries from Patagonia are important to accurately assess global trends in dinosaur diversity, particularly during the latest Cretaceous before the Cretaceous/Paleogene (K/Pg) mass extinction event. Here we describe new theropod dinosaur specimens, representing both associated material and isolated elements, from Upper Cretaceous (Campanian-Maastrichtian) deposits of the Río de las Chinas Valley, Magallanes-Austral Basin, Chile. These discoveries include the southern-most known occurrences of several theropod clades outside of Antarctica, including megaraptorids, unenlagiines, enantiornithines and ornithurines. Notably, these remains provide much needed time-constrained records of smaller theropods, including birds, which are less often recovered from Upper Cretaceous deposits. While fragmentary, these fossils are the first records of theropods from Chilean Patagonia, and provide insight into the distribution of avian and non-avian theropods in southern high latitude ecosystems prior to the K/Pg mass extinction event. Sampling from this region is still sparse, and more fossils from age-controlled sections are needed to accurately assess global extinction dynamics through the end Cretaceous.

New mammalian local faunas from the first ca. 80 ka of the Paleocene in northeastern Montana and a revised model of biotic recovery from the Cretaceous–Paleogene mass extinction

ABSTRACT The earliest phases of mammalian recovery following the Cretaceous–Paleogene (K–Pg) mass extinction are incompletely known but crucial to understanding the development of modern terrestrial ecosystems. Here we report new mammalian faunal data from three vertebrate microfossil assemblages in the Hell Creek region of northeastern Montana, the deposition of which we constrain to within the first 28–80 ka of the Paleocene using new stratigraphic observations within a high-resolution chronostratigraphic framework. We quantified the taxonomic diversity among these three assemblages and five other assemblages from both the Hell Creek region and Denver Basin, together spanning the first ca. 300 ka post-K–Pg mass extinction. Our results allowed us to sub-divide the established ‘disaster’ and ‘recovery’ phases of recovery into the following sub-phases: (i) early disaster, characterized by the presence of ‘dead clades walking,’ high relative abundance of bloom taxa, and the appearance of post-mass-extinction immigrants, (ii) late disaster, characterized by a reduction in the number of ‘dead clades walking,’ continued high relative abundance of bloom taxa, and a more diverse assemblage of immigrants, (iii) early recovery, characterized by decreased relative abundance of bloom taxa, and continued immigration, and (iv) late recovery, characterized by the onset of in situ diversification. We note important differences in the pattern and timing of mammalian faunal succession between the Hell Creek and Denver Basin, suggesting that post-K–Pg mammalian recovery was spatially heterogeneous. Our results provided a new model for post-K–Pg mammalian biotic recovery that can now be tested with other earliest Paleocene assemblages across western North America.

Sedimentary and Diagenetic Controls across the Cretaceous—Paleogene Transition: New Paleoenvironmental Insights of the External Ionian Zone from the Pelagic Carbonates of the Gardiki Section (Epirus, Western Greece)

Field investigation, biostratigraphic, paleoecological, and sedimentary microfacies analyses, as well as diagenetic processes characterization, were carried out in the Epirus region (Western Ionian Basin) to define the depositional environments and further decipher the diagenetic history of the Late Cretaceous–Early Paleocene carbonate succession in western continental Greece. Planktonic foraminiferal biostratigraphy of the studied carbonates revealed that the investigated part of the Gardiki section covers the Cretaceous–Paleogene (K-Pg) transition, partly reflecting the Senonian limestone and calciturbidites formations of the Ionian zone stratigraphy. Litho-and bio-facies analyses allowed for the recognition of three distinct depositional facies: (a) the latest Maastrichtian pelagic biomicrite mudstone with in situ planktonic foraminifera, radiolarians, and filaments, (b) a pelagic biomicrite packstone with abundant planktonic foraminifera at the K-Pg boundary, and (c) an early Paleocene pelagic biomicrite wackestone with veins, micritized radiolarians, and mixed planktonic fauna in terms of in situ and reworked (aberrant or broken) planktonic foraminifera. The documented sedimentary facies characterize a relatively low to medium energy deep environment, representing the transition from the deep basin to the deep shelf and the toe of the slope crossing the K-Pg boundary. Micropaleontological and paleoecological analyses of the samples demonstrate that primary productivity collapse is a key proximate cause of this extinction event. Additional petrographic analyses showed that the petrophysical behavior and reservoir characteristics of the study deposits are controlled by the depositional environment (marine, meteoric, and burial diagenetic) and further influenced by diagenetic processes such as micritization, compaction, cementation, dissolution, and fracturing.

Extinction and survival of raninoid crabs (Decapoda: Brachyura: Raninoida) from the Early Cretaceous to the present

Abstract Faunal turnover is a pattern of diversification and extinction in taxa throughout the geologic record. Patterns of repeated faunal turnovers are referred to as faunal progression, demonstrated by Decapoda in clawed lobsters and podotrematous and heterotrematous crabs. The transition between podotrematous and heterotrematous crabs is the most recent. Among these, section Raninoida Ahyong, Lai, Sharkey, Colgan & Ng, 2007, commonly called “frog crabs,” constitutes a major monophyletic group with podotrematous body forms, and the focus of our study. Declines in raninoidan diversity were aligned with mass extinction events and major climate shifts, especially cooling. Likewise, diversification within Raninoida occurred in warm, greenhouse climates. Thus, a major factor in patterns of faunal turnover in Decapoda is shown to be environmental conditions. Raninoidan families exhibiting adaptations facilitating back-burrowing preferentially survived the end-Cretaceous mass extinction event, whereas raninoidans lacking such adaptions did not go completely extinct at the end-Cretaceous but failed to recover diversity. Given the diversification of heterotrematous crabs into a wide variety of ecological niches throughout the Cenozoic, competition may be a secondary, but still crucial, factor in this faunal turnover.

Renewal of planktonic foraminifera diversity after the Cretaceous Paleogene mass extinction by benthic colonizers

The biotic crisis following the end-Cretaceous asteroid impact resulted in a dramatic renewal of pelagic biodiversity. Considering the severe and immediate effect of the asteroid impact on the pelagic environment, it is remarkable that some of the most affected pelagic groups, like the planktonic foraminifera, survived at all. Here we queried a surface ocean metabarcoding dataset to show that calcareous benthic foraminifera of the clade Globothalamea are able to disperse actively in the plankton, and we show using molecular clock phylogeny that the modern planktonic clades originated from different benthic ancestors that colonized the plankton after the end-Cretaceous crisis. We conclude that the diversity of planktonic foraminifera has been the result of a constant leakage of benthic foraminifera diversity into the plankton, continuously refueling the planktonic niche, and challenge the classical interpretation of the fossil record that suggests that Mesozoic planktonic foraminifera gave rise to the modern communities.

Evidence of large sturgeons in the Paleocene of North America

AbstractRay-finned fishes comprise nearly half of extant vertebrate species and include several ancient lineages with fossil records that stretch over 200 Myr in time. One of these old clades, the sturgeons and paddlefishes, is distributed across the Northern Hemisphere and includes some of the largest known freshwater fishes. Yet, the fossil record of this lineage (Acipenseriformes) is poor compared to similarly ancient ray-finned fish clades. Here, I describe sturgeon fossils from two geological units in North America < 10 Myr younger than the Cretaceous-Paleogene boundary. Both come from individuals of ~1.5 m in length. These Paleogene forms establish the long history of large body size in Acipenseriforms and reveal sturgeons were some of the largest inhabitants of freshwater ecosystems that were still recovering from the Cretaceous-Paleogene extinction.

Low dinosaur biodiversity in central China 2 million years prior to the end-Cretaceous mass extinction

Whether or not nonavian dinosaur biodiversity declined prior to the end-Cretaceous mass extinction remains controversial as the result of sampling biases in the fossil record, differences in the analytical approaches used, and the rarity of high-precision geochronological dating of dinosaur fossils. Using magnetostratigraphy, cyclostratigraphy, and biostratigraphy, we establish a high-resolution geochronological framework for the fossil-rich Late Cretaceous sedimentary sequence in the Shanyang Basin of central China. We have found only three dinosaurian eggshell taxa (Macroolithus yaotunensis, Elongatoolithus elongatus, and Stromatoolithus pinglingensis) representing two clades (Oviraptoridae and Hadrosauridae) in sediments deposited between ∼68.2 and ∼66.4 million y ago, indicating sustained low dinosaur biodiversity, and that assessment is consistent with the known skeletal remains in the Shanyang and surrounding basins of central China. Along with the dinosaur eggshell records from eastern and southern China, we find a decline in dinosaur biodiversity from the Campanian to the Maastrichtian. Our results support a long-term decline in global dinosaur biodiversity prior to 66 million y ago, which likely set the stage for the end-Cretaceous nonavian dinosaur mass extinction.

A compound scenario for the end-Cretaceous mass extinctions

Two major controversies have arisen in research on the end-Cretaceous mass extinctions, concerning the extent to which they were sudden or gradual, and terrestrially or extraterrestrially induced. A review of recent work supports more or less gradual extinction for a number of terrestrial and marine groups such as dinosaurs and-ammonites, but the spectacular crash of the calcareous plankton and correlative ecological disaster in land plants in part of the northern hemisphere suggest a short-term catastrophic event. Chemical and physical signatures of the Cretaceous-Tertiary boundary, including iridium anomalies, shocked quartz, microspherules and carbon, oxygen and strontium isotopes, are discussed and the evidence for and against a bolide impact-induced or volcanic catastrophe is reviewed, with the conclusion that it is not yet decisive either way. Evidence for longer-term changes is also cited, with strontium-isotope data supporting that from stratigraphy in suggesting a significant fall in sea level shortly before the end of the Cretaceous. A large body of evidence also supports a latest Cretaceous fall in seawater and air temperature, but this has recently been disputed for western North America on the basis of leaf studies. It is concluded that both longer term causes, intrinsic to this planet, and a final catastrophe either involving bolide impact or volcanism on a spectacular scale, or perhaps a combination of the two, are required to account for the pattern of end-Cretaceous extinctions.

Clumped-isotope-derived climate trends leading up to the end-Cretaceous mass extinction in northwestern Europe

Abstract. Paleotemperature reconstructions of the end-Cretaceous interval document local and global climate trends, some driven by greenhouse gas emissions from Deccan Traps volcanism and associated feedbacks. Here, we present a new clumped-isotope-based paleotemperature record derived from fossil bivalves from the Maastrichtian type region in southeastern Netherlands and northeastern Belgium. Clumped isotope data document a mean temperature of 20.4±3.8 ∘C, consistent with other Maastrichtian temperature estimates, and an average seawater δ18O value of 0.2±0.8 ‰ VSMOW for the region during the latest Cretaceous (67.1–66.0 Ma). A notable temperature increase at ∼66.4 Ma is interpreted to be a regional manifestation of the globally defined Late Maastrichtian Warming Event, linking Deccan Traps volcanic CO2 emissions to climate change in the Maastricht region. Fluctuating seawater δ18O values coinciding with temperature changes suggest alternating influences of warm, salty southern-sourced waters and cooler, fresher northern-sourced waters from the Arctic Ocean. This new paleotemperature record contributes to the understanding of regional and global climate response to large-scale volcanism and ocean circulation changes leading up to a catastrophic mass extinction.

Massive Loss of Transcription Factors Promotes the Initial Diversification of Placental Mammals.

As one of the most successful group of organisms, mammals occupy a variety of niches on Earth as a result of macroevolution. Transcription factors (TFs), the fundamental regulators of gene expression, may also have evolved. To examine the relationship between TFs and mammalian macroevolution, we analyzed 140,821 de novo-identified TFs and their birth and death histories from 96 mammalian species. Gene tree vs. species tree reconciliation revealed that placental mammals experienced an upsurge in TF losses around 100 million years ago (Mya) and also near the Cretaceous–Paleogene boundary (K–Pg boundary, 66 Mya). Early Euarchontoglires, Laurasiatheria and marsupials appeared between 100 and 95 Mya and underwent initial diversification. The K-Pg boundary was associated with the massive extinction of dinosaurs, which lead to adaptive radiation of mammals. Surprisingly, TF loss decelerated, rather than accelerated, molecular evolutionary rates of their target genes. As the rate of molecular evolution is affected by the mutation rate, the proportion of neutral mutations and the population size, the decrease in molecular evolution may reflect increased functional constraints to survive target genes.

Extreme-sized anurans are more prone to climate-driven extinctions

Understanding species responses to climatic change over extended timescales helps elucidate past and future extinction events. Amphibians are one of the most environmentally sensitive groups and yet showed high resilience to the Cretaceous-Paleogene (KPg) mass extinction, an event marked by sudden cooling and drought. To understand this past resilience and the associated filter mechanisms, we investigated the evolutionary history of key survival traits (body size and lifestyle) and explored climate-driven body-size selectivity of modern anuran assemblages. We found clear environment constraints on present-day anurans, where extreme temperatures and high seasonality filter against extreme-sized species. Our fossil-extant phylogenetic reconstruction reveals that anuran assemblages surrounding the KPg were mostly medium-sized species but large anuran species went extinct at the KPg, which is consistent with the uneven size-resilience to climate across modern anurans. Additionally, we found that cooling periods were marked by accelerated body-size diversification in anurans, and we inferred a close association between the evolution of arboreal frogs and angiosperms. Using the climate resilience of modern species as baselines, we estimate that future climate change will impact tropical anurans the most, where up to ∼500 species may face increased climate-related extinction pressure by 2100. Here we show that size-extinction selectivity in anurans is consistent over time and space, with extreme climate conditions filtering out larger and smaller species, conditions of which are likely to become increasingly prevalent in the future.

Geochemical anomalies caused by meteorite impact and volcanism at the Cretaceous-Paleogene boundary, Wasserfallgraben (Lattengebirge, Germany)

The Cretaceous-Paleogene (K/Pg) mass extinction is the only major mass extinction event that is known to be related to a major meteorite impact (Chicxulub, Mexico) and also occurred during major flood basalt eruptions (Deccan Traps, India). Here, we present geochemical proxies for impact and volcanism analysed in the same sediment samples from the deep-marine sedimentary record of the Gosau Group spanning the K/Pg boundary at Wasserfallgraben, Germany. We measured major and trace elements, including iridium (Ir), tellurium (Te), mercury (Hg), total organic carbon (TOC), and organic carbon isotopes (δ13Corg) on 33 samples from 2 m below to 1.36 m above the K/Pg boundary, a timespan of ∼260 ka. Results show an undisturbed profile, confirmed by changes in calcareous nannofossils assemblages, with a sharp positive Ir peak (2.3 ppb) at the K/Pg boundary (0–10 cm, 25 cm). Volcanic proxies (Hg/TOC, Te/Th) show three distinct peaks not corresponding to the Ir peak, suggesting a volcanic origin, and higher values in the earliest Danian. Compared to the profile in Bidart the proxies of volcanism are less intense in our profile, indicating that the “Deccan Signal” is either diluted or not present in some locations worldwide. The time recorded in the sampled sediments is short (∼0.26 Ma) compared to Deccan flood basalt eruptions (∼1 Ma), but elevated Hg/TOC and Te/Th ratios in the Danian sediments suggests the impact happened prior to the main volcanic outgassing of the Deccan Traps. Our results support the hypothesis that the impact might have triggered the largest, rapidly-erupted Deccan lava formations.

The rise of biting during the Cenozoic fueled reef fish body shape diversification

Diversity of feeding mechanisms is a hallmark of reef fishes, but the history of this variation is not fully understood. Here, we explore the emergence and proliferation of a biting mode of feeding, which enables fishes to feed on attached benthic prey. We find that feeding modes other than suction, including biting, ram biting, and an intermediate group that uses both biting and suction, were nearly absent among the lineages of teleost fishes inhabiting reefs prior to the end-Cretaceous mass extinction, but benthic biting has rapidly increased in frequency since then, accounting for about 40% of reef species today. Further, we measured the impact of feeding mode on body shape diversification in reef fishes. We fit a model of multivariate character evolution to a dataset comprising three-dimensional body shape of 1,530 species of teleost reef fishes across 111 families. Dedicated biters have accumulated over half of the body shape variation that suction feeders have in just 18% of the evolutionary time by evolving body shape ∼1.7 times faster than suction feeders. As a possible response to the ecological and functional diversity of attached prey, biters have dynamically evolved both into shapes that resemble suction feeders as well as novel body forms characterized by lateral compression and small jaws. The ascendance of species that use biting mechanisms to feed on attached prey reshaped modern reef fish assemblages and has been a major contributor to their ecological and phenotypic diversification.

Prolonged morphological expansion of spiny-rayed fishes following the end-Cretaceous.

Spiny-rayed fishes (Acanthomorpha) dominate modern marine habitats and account for more than a quarter of all living vertebrate species. Previous time-calibrated phylogenies and patterns from the fossil record explain this dominance by correlating the origin of major acanthomorph lineages with the Cretaceous-Palaeogene mass extinction. Here we infer a time-calibrated phylogeny using ultraconserved elements that samples 91.4% of all acanthomorph families and investigate patterns of body shape disparity. Our results show that acanthomorph lineages steadily accumulated throughout the Cenozoic and underwent a significant expansion of among-clade morphological disparity several million years after the end-Cretaceous. These acanthomorph lineages radiated into and diversified within distinct regions of morphospace that characterize iconic lineages, including fast-swimming open-ocean predators, laterally compressed reef fishes, bottom-dwelling flatfishes, seahorses and pufferfishes. The evolutionary success of spiny-rayed fishes is the culmination of multiple species-rich and phenotypically disparate lineages independently diversifying across the globe under a wide range of ecological conditions.

First rhynchocephalian (Reptilia, Lepidosauria) from the Cretaceous–Paleogene of India

ABSTRACT Rhynchocephalia, a once diverse clade of lizard-like reptiles, had a nearly global distribution during much of the Mesozoic. By the Late Cretaceous rhynchocephalians underwent a marked reduction in their diversity and biogeographic range, with sparse records of only deeply nested taxa (e.g., Sphenodontinae) found in the Upper Cretaceous–Paleocene of Patagonia and the Miocene–Recent of New Zealand. Here we describe a partial dentary with teeth of a rhynchocephalian from the Naskal locality, an intertrappean deposit within the Deccan Traps Volcanic Province in peninsular India. This discovery represents the first Cretaceous–Paleogene (K–Pg) record of a rhynchocephalian outside of Patagonia and: (i) demonstrates the clade had a broader Gondwanan distribution during the Cretaceous than previously appreciated and (ii) reinforces the emerging pattern that Rhynchocephalia were confined to Gondwana after the Early Cretaceous. This further extends the rhynchocephalian record in India, which now spans most of the Mesozoic (Late Triassic to ca. K–Pg boundary). The Naskal rhynchocephalian is a member of Acrosphenodontia based on its regionalized, acrodont marginal dentition. Its hatchling teeth appear to be unique (e.g., crowns mesially tipped, distinct break in slope along distal margin) and most similar in morphology to those of Godavarisaurus lateefi from the Lower–Middle Jurassic of India. Although the Naskal intertrappean most likely was deposited during the latest Maastrichtian, additional fossil sampling across the K–Pg boundary in India is needed to determine whether the Naskal rhynchocephalian was a victim or survivor of the end-Cretaceous mass extinction.

The choanal anatomy of theSebecus icaeorhinusSimpson, 1937 and the variation of the palatine shape in notosuchians (Crocodyliformes, Mesoeucrocodylia)

AbstractSebecidae is a clade of large carnivorous crocodyliforms that thrived in the Cenozoic and is the only lineage of the diverse and terrestrial group Notosuchia that survived the end-Cretaceous mass extinction event.Sebecus icaeorhinusis the best-known taxon from this clade, both in terms of its cranial and postcranial anatomy (known primarily from the holotype and specimen MPEF-PV 1776, respectively). Additional material represented by a partial skull (MMP 235) is the only specimen that has preserved a complete choanal region. We describe new information from this specimen based on an X-ray computed tomography and identify through comparisons with other taxa a large degree of variability in the palatal anatomy within Sebecidae, in particular in the shape and extension of the palatine (the bone that defines the anterior position and shape of the secondary choana). We quantify variation in the shape of the palatine bone of sebecids through a 2D morphogeometric analysis within the context of notosuchian crocodyliforms. Although traditional accounts of palatal evolution in crocodyliforms linked variation of this structure to the adaptation to the aquatic environment, our analysis allows recognition of eight palatine morphotypes among terrestrial crocodyliforms with very distinct paleoecological traits, including carnivorous, omnivorous, and possibly herbivorous taxa. Furthermore, we show that sebecids had a higher morphological disparity in the choanal region than other terrestrial groups of Notosuchia, underscoring the importance of this region for comparative, morphofunctional, and phylogenetic studies.

Spatial and Temporal Distribution of the Island-Dwelling Kogaionidae (Mammalia, Multituberculata) in the Uppermost Cretaceous of Transylvania (Western Romania)

The latest Cretaceous kogaionid multituberculates from Transylvania (western Romania) were part of an endemic European clade of mammals that underwent an insular radiation at the end of the Cretaceous and then survived the end-Cretaceous mass extinction that extinguished many groups of contemporary therians. Transylvanian kogaionids lived on what was an island during the latest Cretaceous—“Haţeg Island”—and their fossils are found in the uppermost Campanian to upper Maastrichtian deposits of the Haţeg, Rusca Montană, and southwestern Transylvanian basins. This fossil record has improved dramatically over the past several decades, in part resulting from our decade-long joint Romanian-American-Scottish fieldwork, and comprises one of the most impressive and complete archives of Mesozoic mammals, including not only jaws and teeth but several incomplete skulls and partial skeletons. We here review the fossil record of kogaionids from Transylvania. We report four new occurrences from the Haţeg Basin, update information on previously described ones, and use our database to reassess the chronostratigraphical and geographical distribution of kogaionids and their evolutionary patterns. Although it was previously suggested that large and small kogaionids had largely mutually exclusive spatial distributions, we recognize the cooccurrence of small and large taxa in various units, suggesting a sympatric distribution across their entire chronostratigraphic range. We also identify a novel pattern: small kogaionids appear somewhat earlier than their larger relatives in all well-sampled sedimentary successions, suggesting that kogaionid colonizations of Haţeg Island and component regions took place at small body size and that body size increased only later through local evolution. We find correlations between body size, preservation style, and sedimentary context, which give insight into kogaionid paleobiology and diversity. Larger kogaionids are represented more often by partial skulls and occasionally skeletons compared with small kogaionids, which are usually represented only by isolated teeth, regardless of provenance. Larger kogaionids currently have a higher recognized local taxic diversity than their smaller relatives. We hypothesize that this may be in part a consequence of preservational bias related to body size, as more complete specimens may be more easily diagnosed as distinct taxa than those that are represented by more fragmentary and/or incomplete fossils. If true, the taxic diversity of smaller kogaionids may currently be underestimated. Finally, we identify correspondence between sedimentary facies and preservation style. Red-colored fine-grained rocks, suggestive of well-drained, oxidized floodplain paleoenvironments, yield more complete specimens than drab, greenish or grayish sediments deposited in more poorly drained parts of the floodplain. This pattern may suggest habitat preferences for better-drained floodplain environments and a semifossorial lifestyle for some taxa. As the kogaionid fossil record improves, we can further test the hypotheses and patterns outlined above. The pace of new kogaionid discoveries by our team and others indicates that a more complete picture of kogaionid distribution, paleobiology, and evolution will emerge in the coming years, contributing to a more profound understanding of this peculiar group of island-dwelling Mesozoic mammals.

Global ecomorphological restructuring of dominant marine reptiles prior to the Cretaceous-Palaeogene mass extinction.

Mosasaurid squamates were the dominant amniote predators in marine ecosystems during most of the Late Cretaceous. Here, we use a suite of biomechanically rooted, functionally descriptive ratios in a framework adapted from population ecology to investigate how the morphofunctional disparity of mosasaurids evolved prior to the Cretaceous-Palaeogene (K/Pg) mass extinction. Our results suggest that taxonomic turnover in mosasaurid community composition from Campanian to Maastrichtian is reflected by a notable global increase in morphofunctional disparity, especially driving the North American record. Ecomorphospace occupation becomes polarized during the Late Maastrichtian, with morphofunctional disparity plateauing in the Southern Hemisphere and decreasing in the Northern Hemisphere. We show that these changes are not strongly associated with mosasaurid size, but rather with the functional capacities of their skulls. Our novel approach indicates that mosasaurid morphofunctional disparity was in decline in multiple provincial communities before the K/Pg mass extinction, highlighting region-specific patterns of disparity evolution and the importance of assessing vertebrate extinctions both globally and locally. Ecomorphological differentiation in mosasaurid communities, coupled with declines in other formerly abundant marine reptile groups, indicates widespread restructuring of higher trophic levels in marine food webs was well underway when the K/Pg mass extinction took place.