Search Results (11)

Compsemys is an enigmatic turtle first described over 160 years ago. Its taxonomic position has been uncertain, as many of the species placed in the genus have since been removed from it. For the last 30+ years, Compsemys victa has been the only recognized North American fossil species. New fossil specimens collected from the Paleocene in the United States necessitate a re-evaluation of the taxonomy of these turtles and call into question the long-held belief that only one species of Compsemys is valid in North America. Specimens from the Paleocene are far more complete than the holotype of C. victa, and all have been referred to this species based on a similar surface texture. Differences between material from the Cretaceous and Paleocene suggest multiple species of Compsemys are valid. In addition to the genotypic species Compsemys victa, C. puercensis, and C. torrejonensis are both valid species from the Paleocene. Beyond surface sculpturing and texture, features of the carapace and plastron can be used to help differentiate the three species. North American Compsemys survived the Cretaceous–Paleogene mass extinction. Rather than being a monospecific genus, Compsemys diversified in the Paleocene. Not only does this suggest an increase in the diversity of North American compsemydids, but it also leads to the possibility of asymmetric or budding cladogenesis among Compsemys species during the Late Cretaceous and Paleocene, at least in the American Southwest. Full article

Upper Cretaceous–Lower Paleogene successions along the southern Tethyan margin record the combined effects of global environmental perturbations, relative sea-level change, and regional tectonism. This study reconstructs paleoenvironmental and sequence-stratigraphic evolution across Maastrichtian–Ypresian strata in four Esh El-Mellaha sections, northern Eastern Desert, Egypt, using integrated lithostratigraphy, microfacies, benthic foraminiferal assemblages, faunal indices, quantitative paleodepth estimates, and sequence-stratigraphic analysis. The exposed succession comprises the Sudr, Dib, Esna, and Thebes Formations and includes intervals spanning the Cretaceous/Paleogene (K/Pg) boundary and the Paleocene–Eocene Thermal Maximum (PETM). Two major erosional surfaces are recognized: the Sudr/Dib boundary, associated with an incomplete K/Pg transition and a latest Maastrichtian–early Danian hiatus, and the Dib/Esna boundary, related to Late Paleocene erosion/non-deposition during the Selandian–Thanetian interval. Four benthic foraminiferal biofacies indicate deposition mainly in middle-neritic to upper bathyal settings, with pronounced shallowing during Dib Formation deposition. Foraminiferal trophic-oxygen signals indicate contrasting ecological responses, with comparatively oxygenated, low-productivity conditions in the strata bracketing the K/Pg interval and increased organic flux, dysoxia, and opportunistic infaunal taxa during the PETM. Five depositional sequences and five sequence boundaries provide a refined Maastrichtian–Ypresian framework, showing that global eustatic and environmental signals were locally modified by Syrian Arc-related accommodation changes. Full article

Onychophora (velvet worms) are rare, soil-dwelling invertebrates with a fragile body structure that limits their fossil record. Their current distribution across the Neotropics has long been shaped by vicariance and dispersal events. Here, we evaluate the hypothesis that the Cretaceous–Paleogene (K–Pg) asteroid impact played a role in shaping the modern biogeography of Onychophora by eliminating lineages within the affected zone. Using published molecular phylogenies and geological data on the Chicxulub impact, we assess whether extant clades are congruent with a post-impact recolonization scenario. We find that several clades have divergence dates incompatible with extinction at the K–Pg boundary and that current distributions do not show a clear biogeographic signature consistent with impact-induced extirpation. Our hypothesis test supports the survival of onychophoran lineages through the K–Pg event and calls for caution in attributing modern distributions to a single extinction event without integrating molecular, stratigraphic, and ecological data. Full article

Physical dormancy (PY) due to a water-impermeable seed/fruit coat is one of the characteristic features of many species of Fabaceae; however, the timing and context of the evolution of this trait are poorly understood. In this investigation, fossil and molecular data are used to constrain the timing of the evolution of PY. The phylogenetic reconstruction programs GB-to-TNT and BEAUTi/BEAST are used to create chloroplast gene-based (rbcL and matK) phylogenies of taxa with well-represented fossil records. PY and non-dormancy are mapped to the terminals of the phylogeny, and ancestral states are reconstructed using parsimony. The initial evolution of PY in Fabaceae is reconstructed to have occurred sometime in the interval between divergence from Polygalaceae (late Campanian) to the diversification of crown-group Fabaceae (late Paleocene) when Fabaceae is known to have undergone multiple whole genome duplication (WGD) events across the Cretaceous/Paleogene (K/Pg) boundary. As in Nelumbo, another taxon with PY, Fabaceae may have developed PY in association with climatic change and WGD across the K/Pg boundary. The evolution of PY in association with WGD at the K/Pg boundary is an intriguing hypothesis that requires further investigation. Full article

The boundary between Cretaceous and Paleogene (K/Pg) plays an important role in deciphering the Earth’s history and biological evolution from Mesozoic to Cenozoic. As such, the delineation and characterization of the boundary layer has attracted significant attention. In this study, X-ray diffraction (XRD) and elemental analyses were conducted to characterize the samples of boundary layer and the layers around Agost and Caravaca, Spain. The XRD results showed that the layers immediately above and below the boundary layer are made of limestone, while in the boundary layer, a significant increase in the clay minerals smectite, kaolinite, and illite was observed. The major element analyses revealed an increase in Si and Al contents, confirming the presence of clay minerals. The trace element analyses showed elevated concentrations of V, Cr, Ni, Zn, Pb, and Th, but not for Rb, Cu, and U. The rare Earth element (REE) analyses showed elevated La, Ce, and Nd concentrations in the boundary layer. Correlation analyses between selected trace elements and REE showed good agreements, with R² values of about 0.9. The results agreed well with the finding in the area, except the lower contents of Rb, Cu, and U; thus, they may promote further studies to make detailed comparisons. Full article

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. Full article

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. Full article

Around 80% of megaflora species became extinct at the Cretaceous–Paleogene (K–Pg) boundary. Subsequent polyploidy events drove the survival of thousands of plant species and played a significant historical role in the development of the most successful modern cereal crops. However, current and rapid global temperature change poses an urgent threat to food crops worldwide, including the world’s big three cereals: rice, wheat, and maize, which are members of the grass family, Poaceae. Some minor cereals from the same family (such as teff) have grown in popularity in recent years, but there are important knowledge gaps regarding the similarities and differences between major and minor crops, including how polyploidy affects their biological processes under natural and (a)biotic stress conditions and thus the potential to harness polyploidization attributes for improving crop climate resilience. This review focuses on the impact of polyploidy events on the Poaceae family, which includes the world’s most important food sources, and discusses the past, present, and future of polyploidy research for major and minor crops. The increasing accessibility to genomes of grasses and their wild progenitors together with new tools and interdisciplinary research on polyploidy can support crop improvement for global food security in the face of climate change. Full article

The extant diversity of the avian clade Palaeognathae is composed of the iconic flightless ratites (ostriches, rheas, kiwi, emus, and cassowaries), and the volant tinamous of Central and South America. Palaeognaths were once considered a classic illustration of diversification driven by Gondwanan vicariance, but this paradigm has been rejected in light of molecular phylogenetic and divergence time results from the last two decades that indicate that palaeognaths underwent multiple relatively recent transitions to flightlessness and large body size, reinvigorating research into their evolutionary origins and historical biogeography. This revised perspective on palaeognath macroevolution has highlighted lingering gaps in our understanding of how, when, and where extant palaeognath diversity arose. Towards resolving those questions, we aim to comprehensively review the known fossil record of palaeognath skeletal remains, and to summarize the current state of knowledge of their evolutionary history. Total clade palaeognaths appear to be one of a small handful of crown bird lineages that crossed the Cretaceous-Paleogene (K-Pg) boundary, but gaps in their Paleogene fossil record and a lack of Cretaceous fossils preclude a detailed understanding of their multiple transitions to flightlessness and large body size, and recognizable members of extant subclades generally do not appear until the Neogene. Despite these knowledge gaps, we combine what is known from the fossil record of palaeognaths with plausible divergence time estimates, suggesting a relatively rapid pace of diversification and phenotypic evolution in the early Cenozoic. In line with some recent authors, we surmise that the most recent common ancestor of palaeognaths was likely a relatively small-bodied, ground-feeding bird, features that may have facilitated total-clade palaeognath survivorship through the K-Pg mass extinction, and which may bear on the ecological habits of the ancestral crown bird. Full article

Assessing the applicability of theory to major adaptive radiations in deep time represents an extremely difficult problem in evolutionary biology. Neoaves, which includes 95% of living birds, is believed to have undergone a period of rapid diversification roughly coincident with the Cretaceous–Paleogene (K-Pg) boundary. We investigate whether basal neoavian lineages experienced an ecological release in response to ecological opportunity, as evidenced by density compensation. We estimated effective population sizes (Ne) of basal neoavian lineages by combining coalescent branch lengths (CBLs) and the numbers of generations between successive divergences. We used a modified version of Accurate Species TRee Algorithm (ASTRAL) to estimate CBLs directly from insertion–deletion (indel) data, as well as from gene trees using DNA sequence and/or indel data. We found that some divergences near the K-Pg boundary involved unexpectedly high gene tree discordance relative to the estimated number of generations between speciation events. The simplest explanation for this result is an increase in Ne, despite the caveats discussed herein. It appears that at least some early neoavian lineages, similar to the ancestor of the clade comprising doves, mesites, and sandgrouse, experienced ecological release near the time of the K-Pg mass extinction. Full article

It has long been appreciated that analyses of genomic data (e.g., whole genome sequencing or sequence capture) have the potential to reveal the tree of life, but it remains challenging to move from sequence data to a clear understanding of evolutionary history, in part due to the computational challenges of phylogenetic estimation using genome-scale data. Supertree methods solve that challenge because they facilitate a divide-and-conquer approach for large-scale phylogeny inference by integrating smaller subtrees in a computationally efficient manner. Here, we combined information from sequence capture and whole-genome phylogenies using supertree methods. However, the available phylogenomic trees had limited overlap so we used taxon-rich (but not phylogenomic) megaphylogenies to weave them together. This allowed us to construct a phylogenomic supertree, with support values, that included 707 bird species (~7% of avian species diversity). We estimated branch lengths using mitochondrial sequence data and we used these branch lengths to estimate divergence times. Our time-calibrated supertree supports radiation of all three major avian clades (Palaeognathae, Galloanseres, and Neoaves) near the Cretaceous-Paleogene (K-Pg) boundary. The approach we used will permit the continued addition of taxa to this supertree as new phylogenomic data are published, and it could be applied to other taxa as well. Full article