Some articles in Japanese with free pdfs from last year (2018) not yet mentioned. These come from a special section in an issue of the open access Japanese Journal of Ornithology.Â
Japanese Journal of Ornithology
Japanese Journal of Ornithology 67(1) (2018)
In Japanese with English abstracts
The origin of birds has been a fundamental and challenging subject in ornithology since the discovery of Archaeopteryx. Although the phylogenetic relationship between birds and crocodiles has been recognized since the beginning of discussion, researchers were unable to reached a consensus as to which was the ancestor of modern birds. Pterosauria, Crocodilia, Thecodont, Ornithischia, and Theropoda have all been put forward as the ancestors of birds. Recent paleontological studies have clarified that birds are derived from a clade of Maniraptora in the clade Coelurosauria among the Theropod dinosaurs. Fossil evidence has demonstrated that birds share several features with Coelurosauria dinosaurs, such as bipedal locomotion, fork-shaped furcula, air sacs, and laterally flexing wrists. Embryological and molecular biological evidence correspond with this view. Today, birds are phylogenetically defined as avian dinosaurs, and other dinosaurs are defined as non-avian dinosaurs. This implies that dinosaurs did not become extinct at the end of the Cretaceous period, 66 million years ago. Feathered dinosaurs represent one of the most remarkable topics of recent paleontology. Various dinosaurs with contour feathers have been found among the Coelurosauria, while simple filament-like protofeathers have been detected in an even wider range of taxa, including the Ornithischia. Furthermore, flightless Ornithomimus edmontonicus has been shown to have possessed pennaceous wings. These findings imply that non-avian dinosaurs evolved feathers and wings for rea- sons unrelated to flight, perhaps for display. While toothless beaks, the pygostyle, short- ened tails, and keeled sternums are considered to have evolved for flight, bipedalism, air sacs, and furcula are considered to be cases of exaptation. The fields of ornithology and paleontology may contribute to each other based on the close relationships between birds and dinosaurs. Collaboration between these two fields is essential for their future development. Â
Archosaurs (e.g., crocodilians, pterosaurs, and dinosaurs including birds) are the most diverse and successful clade of terrestrial vertebrates. An understanding of the nesting methods and behaviors of both extinct (e.g., non-avian dinosaurs) and extant archosaurs (i.e., crocodilians and birds) is crucial for the advancement of our understanding of the evolution and diversification of this clade. The nesting methods and behavior of extinct taxa cannot be directly observed from the fossil record, thus aspects of nesting (i.e., nest type, incubation behavior, and incubation period) may only be inferred and reconstructed based on certain features of fossil eggs, nests, and embryos (e.g., clutch size, egg mass, eggshell porosity, and embryonic osteology). Nests and nesting behaviors were likely to have been diverse among non-avian dinosaurs, and the evolution of these features in archosaurs is discussed. Â
Since the 1990s, the avian fossil record has been greatly advanced with the oldest record found from the Upper Jurassic and a pan-global distribution discovered in the Cretaceous. Birds possess highly modified skeletal characteristics such as the pygostyle, keeled sternum, forelimbs developed as wings, and toothless jaws, all of which are considered to have evolved in relation to flight. Recent discoveries have also revealed that Mesozoic birds had made various ecological developments including sexual dimorphism and differential growth rates. Although the reasons for the limited diversification of flightless birds in the Mesozoic and for the survival of the Neornithes through the K-Pg mass extinction event are still not well understood, they may be attributed to environmental and physiological limitations. In this paper, I suggest that the development of flight capability, endothermy, and efficient digestive systems may have been involved in the diversification and wide geographical distribution of birds. Although physiological characteristics are rarely preserved in the fossil record, new fossil discoveries and advancements in research on soft tissue reconstruction might reveal more details of the ecology of extinct birds in the near future. Â
Hesperornithiformes were toothed, foot-propelled diving birds and among the most widely distributed groups of birds in the Cretaceous (Late Albian to Maastrichtian) in the Northern Hemisphere. The first species of this group, Hesperornis regalis was discovered from the Niobrara Formation (Upper Santonian) in Kansas in 1871. H. regalis had extremely reduced forelimbs, powerful hind limbs, and a non-keeled sternum. Taking into consideration the osteological features mentions above, this huge diving bird was obviously a flightless foot-propelled diver. Currently, Cretaceous Hesperornithiformes are recognized as the oldest diving birds in the avian evolutionary history. Thirty-one species and at least fifteen genera have been named so far. Most of the known hesperornithiform remains have been recovered from the marine deposits of the Western Interior Seaway in North America, especially from Kansas and South Dakota in USA and Manitoba and Saskatchewan in Canada. In Europe, some hesperornithiform remains have been found from the Cretaceous deposits of the Turgai Strait (Russia and Kazakhstan), but Hesperornithiformes are extremely rare in Asia where they are only known from three remains from Mongolia and Japan. Current phylogenetic analyses of Mesozoic birds suggest that these diving birds are one of the closest relatives of the Neornithes (modern birds). In this article, we review the current knowledge of the origin of the Neornithes, the phylogeny of Mesozoic birds, and hesperornithiform osteology and paleoecology. We also discuss future prospects for research into these oldest diving birds.