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      Maaqwi cascadensis: A large, marine diving bird (Avialae: Ornithurae) from the Upper Cretaceous of British Columbia, Canada

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          Abstract

          Mesozoic bird fossils from the Pacific Coast of North America are rare, but small numbers are known from the Late Cretaceous aged sediments of Hornby Island, British Columbia. Most are unassociated fragments that offer little information, but additional preparation of a large coracoid has revealed more details of its structure, as well as three associated wing bones. Phylogenetic analysis suggests that Maaqwi cascadensis, gen. et sp. nov. represents a derived crown or near-crown member of Ornithurae, and specifically suggests affinities with Vegaviidae. M. cascadensis is characterized by large size, and regressions based on dimensions of the coracoid suggest a large bird, with an estimated body mass of approximately 1.5 kilograms. The bones are robust, with thick walls, suggesting that M. cascadensis was a bird adapted for diving, similar to modern loons and grebes. The wings are short, while the coracoid is unusually short and broad, similar to modern loons. Along with the Ichthyornithes and Hesperornithes, M. cascadensis and Vegaviidae appear to represent a third clade of bird that evolved to exploit marine habitats in the Late Cretaceous, one specialized for foot-propelled diving and rapid cruising flight over water.

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          MORPHOLOGY, PHYLOGENETIC TAXONOMY, AND SYSTEMATICS OF ICHTHYORNIS AND APATORNIS (AVIALAE: ORNITHURAE)

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            Mass extinction of birds at the Cretaceous-Paleogene (K-Pg) boundary.

            The effect of the Cretaceous-Paleogene (K-Pg) (formerly Cretaceous-Tertiary, K-T) mass extinction on avian evolution is debated, primarily because of the poor fossil record of Late Cretaceous birds. In particular, it remains unclear whether archaic birds became extinct gradually over the course of the Cretaceous or whether they remained diverse up to the end of the Cretaceous and perished in the K-Pg mass extinction. Here, we describe a diverse avifauna from the latest Maastrichtian of western North America, which provides definitive evidence for the persistence of a range of archaic birds to within 300,000 y of the K-Pg boundary. A total of 17 species are identified, including 7 species of archaic bird, representing Enantiornithes, Ichthyornithes, Hesperornithes, and an Apsaravis-like bird. None of these groups are known to survive into the Paleogene, and their persistence into the latest Maastrichtian therefore provides strong evidence for a mass extinction of archaic birds coinciding with the Chicxulub asteroid impact. Most of the birds described here represent advanced ornithurines, showing that a major radiation of Ornithurae preceded the end of the Cretaceous, but none can be definitively referred to the Neornithes. This avifauna is the most diverse known from the Late Cretaceous, and although size disparity is lower than in modern birds, the assemblage includes both smaller forms and some of the largest volant birds known from the Mesozoic, emphasizing the degree to which avian diversification had proceeded by the end of the age of dinosaurs.
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              "Pachyostosis" in aquatic amniotes: a review.

              During the course of amniote evolution, numerous taxa secondarily adapted to an aquatic life. It appears that many of these taxa primitively display "pachyostosis," an osseous specialization characterized by an increase in bone compactness and/or volume. The term "pachyostosis" is used in morphological and histological descriptions to describe what in fact corresponds to different patterns. The aim of this paper is to present the current state of knowledge relative to this adaptation among aquatic amniotes. All the taxa that have returned to an aquatic environment are listed. Moreover, their degree of adaptation to the marine environment, their life environment, and the nature of their "pachyostotic" pattern, when present, are described. This inventory enables the evaluation of the current quality of the data relative to this specialization and provides an indication of the work that remains to be done. The functional consequences of "pachyostosis," and notably its importance for buoyancy control in the context of hydrostatic regulation of the body trim, are discussed and opposed to the requirement of improved swimming abilities in the case of a hydrodynamic mode of trim regulation. Questions are posed about the signification of the polymorphism displayed by this specialization between different taxa, different specimens of the same taxon and different bones of the same specimen, and the problem of quantification of pachyostosis is discussed. © 2009 ISZS, Blackwell Publishing and IOZ/CAS.
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                Author and article information

                Contributors
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: Project administrationRole: ResourcesRole: SoftwareRole: VisualizationRole: Writing – original draftRole: Writing – review & editing
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: Writing – original draftRole: Writing – review & editing
                Role: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: SoftwareRole: VisualizationRole: Writing – review & editing
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                8 December 2017
                2017
                : 12
                : 12
                : e0189473
                Affiliations
                [1 ] School of Earth & Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada
                [2 ] Department of Natural History, Royal BC Museum, Victoria, British Columbia, Canada
                [3 ] Department of Biology and Biochemistry, and Milner Centre for Evolution, University of Bath, Bath, United Kingdom
                University of Michigan, UNITED STATES
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Author information
                http://orcid.org/0000-0003-3902-7190
                Article
                PONE-D-17-09464
                10.1371/journal.pone.0189473
                5722380
                29220405
                de7aeb0d-d5f9-4d00-b005-27f5b103a48b
                © 2017 McLachlan et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 9 March 2017
                : 28 November 2017
                Page count
                Figures: 8, Tables: 1, Pages: 18
                Funding
                The authors received no specific funding for this work.
                Categories
                Research Article
                Biology and Life Sciences
                Organisms
                Eukaryota
                Animals
                Vertebrates
                Amniotes
                Birds
                Biology and Life Sciences
                Anatomy
                Musculoskeletal System
                Skeleton
                Humerus
                Medicine and Health Sciences
                Anatomy
                Musculoskeletal System
                Skeleton
                Humerus
                Biology and Life Sciences
                Zoology
                Animal Anatomy
                Wings
                Biology and Life Sciences
                Physiology
                Biological Locomotion
                Flight (Biology)
                Bird Flight
                Medicine and Health Sciences
                Physiology
                Biological Locomotion
                Flight (Biology)
                Bird Flight
                Biology and Life Sciences
                Zoology
                Ornithology
                Bird Flight
                Earth Sciences
                Geology
                Geologic Time
                Mesozoic Era
                Cretaceous Period
                Biology and Life Sciences
                Paleontology
                Fossils
                Marine Fossils
                Earth Sciences
                Paleontology
                Fossils
                Marine Fossils
                Earth Sciences
                Geomorphology
                Topography
                Landforms
                Islands
                Biology and Life Sciences
                Ecology
                Paleoecology
                Ecology and Environmental Sciences
                Ecology
                Paleoecology
                Biology and Life Sciences
                Paleontology
                Paleobiology
                Paleoecology
                Earth Sciences
                Paleontology
                Paleobiology
                Paleoecology
                Custom metadata
                All relevant data are within the paper and its Supporting Information files. The fossil material described is housed within the Royal BC Museum (Victoria, British Columbia, Canada) under the accession number RBCM.EH2008.011.01120. Modern materials from which measurements were obtained are also housed in the University of Washington Burke Museum (Seattle, Washington).

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