ABSTRACT Basal Ornithuromorpha, until recently, was one of the most poorly documented segments of early avian evolution. The known species diversity of the ornithuromorph clade has increased rapidly with the addition of new discoveries from the Early Cretaceous deposits of northeastern China. Reported in this paper is the discovery of a new bird from the Lower Cretaceous Yixian Formation, Liaoning Province, China. The specimen represents a new species, Longicrusavis houi, but bears similarities to Hongshanornis longicresta from the same formation of Inner Mongolia. The two birds are comparable in size and share an unusual sigmoid mandible and elongate hindlimbs relative to their forelimbs. Together these taxa represent a clade (Hongshanornithidae, new taxon) of specialized 'shorebirds' whose elongate hindlimbs indicate ecological adaptations different from those of other Jehol ornithuromorphs. Phylogenetic relationships of Mesozoic birds are discussed based on the results of a comprehensive cladistic analysis. New morphological information on Ornithuromorpha is provided through the detailed description of the new taxon together with new information on Hongshanornis.
The origin of bird and avian flight is one of the most controversial debates since the fossil of Archaeopteryx was found in Germany. With the continuous discoveries of relative fossils of dinosaurs from all over the world, scientists have reached a consensus that the ancestors of bird might be small sized non-avian theropod dinosaurs. However, the disputation focus now remains in how the dinosaur learned to fly. Via analysis of kinematics and dynamics of reconstructed Caudipteryx robot on the test rig, we discovered that the flapping motion of the forearms of feathered dinosaurs was developed as they were only able to run on the ground when it was long before it could actually fly in the sky. This study supports the inferences that the performance of powered flapping flight was evolved long before the feathered dinosaurs could fly. This is a completely natural biophysical principle that provides a vital role to comprehend the evolution of avian flight.
Since the first skeletal remains of avians preserved in amber were described in 2016, new avian remains trapped in Cretaceous-age Burmese amber continue to be uncovered, revealing a diversity of skeletal and feather morphologies observed nowhere else in the Mesozoic fossil record. Here we describe a foot with digital proportions unlike any previously described enantiornithine or Mesozoic bird. No bones are preserved in the new specimen but the outline of the foot is recorded in a detailed skin surface, which is surrounded by feather inclusions including a partial rachis-dominated feather. Pedal proportions and plumage support identification as an enantiornithine, but unlike previous discoveries the toes are stout with transversely elongated digital pads, and the outer toe appears strongly thickened relative to the inner two digits. The new specimen increases the known diversity and morphological disparity among the Enantiornithes, hinting at a wider range of habitats and behaviours. It also suggests that the Burmese amber avifauna was distinct from other Mesozoic assemblages, with amber entrapment including representatives from unusual small forms.
As key components of the tetrapod pectoral girdle, the scapula and coracoid have played a significant role in the evolution of forelimb locomotion among terrestrial vertebrates. The transition from a rigid fused scapulocoracoid in ancestral non-avian theropods to a presumably more flexible separated scapula-coracoid in early birds is considered to be one of the key morphological transitions related to the rapid refinement of flight. In most Mesozoic birds (e.g., Enantiornithes and Ornithuromorpha) and crown birds the scapula and coracoid are separate (unfused), with few exceptions (e.g., flightless paleognaths). In contrast, in Confuciusornis , a basal pygostylian from the Early Cretaceous Jehol Biota known from thousands of specimens, the scapula and coracoid remain plesiomorphically fused. This raises questions regarding the influence of shoulder girdle architecture on the early evolution and refinement of avian flight. The paravian scapula-coracoid joint has never previously been investigated using histology, and thus joint morphology has only been inferred superficially. In order to better understand the evolution of this joint in Mesozoic birds, we make the first histological study of the scapulocoracoid glenoid joint in Confuciusornis . The results demonstrate that the scapula and coracoid both consist of cancellous and compact bone, with both fibrolamellar and parallel-fibered structure. A thin layer of calcified cartilage is present on the glenoid fossa surface, representing remnants of the articular surface for the humerus. Both histology and computed tomography reveal that the scapulocoracoid of Confuciusornis is fully fused, forming a synostosis. Humeral histology suggests the studied individual was nearing completion of its first year of growth, suggesting the Confuciusornis scapulocoracoid fused before skeletal maturity was achieved, as in flightless paleognaths, whereas in the plesiomorphic condition fusion occurs late in ontogeny. We hypothesize the fused scapulocoracoid of Confuciusornis is secondarily evolved and suggest the primary factor responsible for this morphology may have been a decrease in mechanical stimulation at the glenoid of Confuciusornis relative to other volant birds, linked to the unique flight style of this taxon. Further investigation into the histology of the glenoid joint in other Mesozoic paravians and extant birds will help to clarify the morphological transition of the scapula-coracoid joint in early avian evolution.
ABSTRACTWe describe a new enantiornithine bird, Fortunguavis xiaotaizicus, gen. et sp. nov, from the Lower Cretaceous lacustrine deposits of the Jiufotang Formation in northeastern China. The new taxon has a strongly dorsoventrally bowed furcula indicating that enantiornithines evolved furcular morphologies in parallel with ornithuromorphs. The new specimen has very robust limbs compared with other enantiornithines and has an unique foot morphology with metatarsal II much shorter than metatarsal IV, robust pedal digits, and strongly recurved pedal unguals. Although recurved unguals characterize Enantiornithes, the extreme curvature present in Fortunguavis suggests scansorial specialization in this species. These features hint at a unique ecology for this taxon and further increase the known diversity of body plans in Early Cretaceous enantiornithines.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at http://www.tandfonline.com/UJVP.
ABSTRACTWe describe a new isolated tarsometatarsus from the Early Cretaceous (Barremian-Aptian) Ilek Formation Shestakovo-3 locality in western Siberia. The new specimen represents a new taxon, Evgenavis nobilis, gen. et sp. nov., significantly increasing the Mesozoic avifauna from Russia. The specimen shares morphologies with a number of basal ornithothoracine taxa, but shows most similarity to the basal pygostylian Confuciusornis sanctus, the oldest known beaked bird and most common taxon from the Yixian Formation. Evgenavis may represent the first record of Confuciusornithiformes outside of the Jehol Group and its equivalent deposits. However, this is not supported by cladistic analysis, which weakly resolves the new species and Mystiornis both within the diverse Enantiornithes, indicating that additional material is required to assess the systematic position of Evgenavis nobilis (Aves incertae sedis). The three-dimensional preservation of the specimen allows for a partial reconstruction of the pedal musculature, revealing a primitive stage in the evolution of the neornithine condition.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at http://www.tandfonline.com/UJVP.
Abstract We welcome any new interpretation or alternative hypothesis regarding the taxonomic affinity of the enigmatic Oculudentavis khaungraae . However, here we demonstrate that Li et al. have failed to provide conclusive evidence for the reidentification of HPG-15-3 as a squamate. We analyse this specimen in a matrix that includes a broad sample of diapsid reptiles and resolve support for this identification only when no avian taxa are included. Regardless of whether this peculiar skull belongs to a tiny bird or to a bizarre new group of lizards, the holotype of Oculudentavis khaungraae is a very interesting and unusual specimen, the discovery of which represents an important contribution to palaeontology. Its discovery documents a potential new case of convergent evolution in reptiles, while highlighting the importance of amber deposits for documenting taxa not recorded in sedimentary deposits.
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