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1.
A partial skeleton of a primitive bird, Rahona ostromi, gen. et sp. nov., has been discovered from the Late Cretaceous of Madagascar. This specimen, although exhibiting avian features such as a reversed hallux and ulnar papillae, retains characteristics that indicate a theropod ancestry, including a pubic foot and hyposphene-hypantra vertebral articulations. Rahona has a robust, hyperextendible second digit on the hind foot that terminates in a sicklelike claw, a unique characteristic of the theropod groups Troodontidae and Dromaeosauridae. A phylogenetic analysis places Rahona with Archaeopteryx, making Rahona one of the most primitive birds yet discovered. 相似文献
2.
Fossil evidence for changes in dinosaurs near the lineage leading to birds and the origin of flight has been sparse. A dinosaur from Mongolia represents the basal divergence within Dromaeosauridae. The taxon's small body size and phylogenetic position imply that extreme miniaturization was ancestral for Paraves (the clade including Avialae, Troodontidae, and Dromaeosauridae), phylogenetically earlier than where flight evolution is strongly inferred. In contrast to the sustained small body sizes among avialans throughout the Cretaceous Period, the two dinosaurian lineages most closely related to birds, dromaeosaurids and troodontids, underwent four independent events of gigantism, and in some lineages size increased by nearly three orders of magnitude. Thus, change in theropod body size leading to flight's origin was not unidirectional. 相似文献
3.
Archaeopteryx is almost universally considered a primitive bird. Debate persists, however, about the taxonomic assignment of the six skeletal fossils. Allometric scaling of osteological data shows that all specimens are consistent with a single growth series. The absence of certain bone fusions suggests that no specimen is full-grown. Allometric patterns, as compared to growth gradients of other dinosaurs, extant ectotherms, and extant endotherms, suggest that Archaeopteryx was likely a homeothermic endotherm with rapid growth and precocial abilities for running and flying. Multivariate allometric models offer a significant potential for interpreting ontogenetic patterns and phylogenetic trends in the fossil record. 相似文献
4.
Both Hesperornis and Ichthyornis are toothed birds; they and Archaeopteryx share broad flattened teeth with highly expanded roots. The teeth of Ichthyornis have been reported to have been set in sockets as were those of Archaeopteryx, but new specimens of Ichthyornis show the teeth set in a groove as in Hesperornis. These new fossils are from an adult but not old bird; thus, the presence or absence of tooth sockets in birds may be dependent on age. 相似文献
5.
Some nonavian theropod dinosaurs were at least partially covered in feathers or filamentous protofeathers. However, a complete understanding of feather distribution among theropod dinosaurs is limited because feathers are typically preserved only in lagerst?tten like that of Solnhofen, Germany or Liaoning, China. Such deposits possess clear taphonomic biases toward small-bodied animals, limiting our knowledge regarding feather presence in larger members of feathered clades. We present direct evidence of feathers in Velociraptor mongoliensis based on the presence of quill knobs on the posterior forearm. This report of secondaries in a larger-bodied, derived, and clearly flightless member of a nonavian theropod clade represented by feathered relatives is a substantial contribution to our knowledge of the evolution of feathers. 相似文献
6.
Feduccia A 《Science (New York, N.Y.)》1993,259(5096):790-793
The Late Jurassic Archaeopteryx has been thought to have been a feathered predator adapted to running that represented a terrestrial stage in the evolution of true birds from coelurosaurian dinosaurs. Examination of claw geometry, however, shows that (i) modern ground- and tree-dwelling birds can be distinguished on the basis of claw curvature, in that greater claw arcs characterize tree-dwellers and trunk-climbers, and (ii) the claws of the pes (hind foot) and manus (front hand) of Archaeopteryx exhibit degrees of curvature typical of perching and trunk-climbing birds, respectively. On this basis, Archaeopteryx appears to have been a perching bird, not a cursorial predator. 相似文献
7.
Jurassic fossil vertebrates collected from the Falla Formation in the Central Transantarctic Mountains included a partial skull and postcranial elements of a crested theropod, Cryolophosaurus ellioti gen. nov. sp. nov. The theropod bears some resemblance to the large tetanurans of the Middle to Late Jurassic but also has primitive ceratosaurian features. Elements from a prosauropod, teeth from scavenging theropods, a pterosaur humerus, and a tritylodont molar were also recovered. The presence of this fauna suggests that a mild climate existed at high paleolatitude in this area of Gondwana during the Early Jurassic. 相似文献
8.
Stokstad E 《Science (New York, N.Y.)》2000,290(5498):1871-1872
Chinese paleontologists studying the fossil known as Microraptor describe it as both the smallest and the most birdlike dinosaur yet discovered. In this week's issue of Nature, they say the crow-sized, feathered creature--whose fossilized tail once formed part of a now-discredited "missing link" between birds and dinosaurs known as Archaeoraptor--belongs to the dromaeosaurs, dinosaurs that many paleontologists consider the closest dinosaurian relatives of birds. 相似文献
9.
Charig AJ Greenaway F Milner AC Walker CA Whybrow PJ 《Science (New York, N.Y.)》1986,232(4750):622-626
Archaeopteryx lithographica might be regarded as the most important zoological species known, fossil or recent. Its importance lies not in that its transitional nature is unique-there are many such transitional forms at all taxonomic levels-but in the fact that it is an obvious and comprehensible example of organic evolution. There have been recent allegations that the feather impressions on Archaeopteryx are a forgery. In this report, proof of authenticity is provided by exactly matching hairline cracks and dendrites on the feathered areas of the opposing slabs, which show the absence of the artificial cement layer into which modern feathers could have been pressed by a forger. 相似文献
10.
Wellnhofer P 《Science (New York, N.Y.)》1988,240(4860):1790
A new specimen of the primordial bird Archaeopteryx is reported from the Upper Jurassic Solnhofen Limestone of Bavaria. This "Solnhofen specimen" is the largest of now six skeletal specimens and shows dose similarities with the London specimen. It is therefore assigned to Archaeopteryx lithographica Meyer. Clear impressions of the feather shafts of the left wing are preserved. 相似文献
11.
Paul GS 《Science (New York, N.Y.)》2010,330(6002):320; author reply 320
Nudds and Dyke (Reports, 14 May 2010, p. 887) compared the rachis diameters of the primary feathers of Archaeopteryx and Confuciusornis to those of modern birds and found that the primary feathers of these two basal birds were too weak to support sustained flight. Our measurements of Confuciusornis specimens suggest that their conclusions need to be further evaluated. 相似文献
12.
On the basis of new information from the 10th specimen of Archaeopteryx, Mayr et al. (Reports, 2 December 2005, p. 1483) suggested that birds, or avian flight, originated twice. We investigate the statistical support for this phylogenetic hypothesis and show that it is no better supported by available morphological character data than the hypothesis of a single avian origin. 相似文献
13.
Ostrom JH 《Science (New York, N.Y.)》1970,170(3957):537-538
A fourth specimen of Archaeopteryx (cf. lithographica), the oldest known fossil bird, was recently found in the collections of the Teyler Museum in the Netherlands. Unique preservation of the horny sheaths of the manus claws provides new evidence that may be relevant to the question of the origins of avian flight. Tentative interpretation suggests a cursorial rather than arboreal origin. 相似文献
14.
An oviraptosaurian specimen (Dinosauria, Theropoda) from an Upper Cretaceous formation in China retains a pair of shelled eggs in the pelvis, providing direct evidence that oviraptorosaurian dinosaurs laid paired elongatoolithid eggs. The presence of the paired eggs suggests that theropod dinosaurs had two functional oviducts (like crocodiles) but that each oviduct produced only one egg at a time and that an entire egg clutch was laid through multiple ovipositions (like birds). The orientations of the eggs inside the skeleton and in clutches indicate that the mother came to the center of the nest to lay eggs. 相似文献
15.
Vanes in the primary flight feathers of Archaeopteryx conform to the asymmetric pattern in modern flying birds. The asymmetry has aerodynamic functions and can be assumed to have evolved in the selective context of flight. 相似文献
16.
Predatory dinosaur remains from madagascar: implications for the cretaceous biogeography of gondwana 总被引：1，自引：0，他引：1
SD Sampson LM Witmer CA Forster DW Krause PM O'Connor P Dodson F Ravoavy 《Science (New York, N.Y.)》1998,280(5366):1048-1051
Recent discoveries of fossil vertebrates from the Late Cretaceous of Madagascar include several specimens of a large theropod dinosaur. One specimen includes a nearly complete and exquisitely preserved skull with thickened pneumatic nasals, a median frontal horn, and a dorsal projection on the parietals. The new materials are assigned to the enigmatic theropod group Abelisauridae on the basis of a number of unique features. Fossil remains attributable to abelisaurids are restricted to three Gondwanan landmasses: South America, Madagascar, and the Indian subcontinent. This distribution is consistent with a revised paleogeographic reconstruction that posits prolonged links between these landmasses (via Antarctica), perhaps until late in the Late Cretaceous. 相似文献
17.
Late Jurassic and Early Cretaceous birds from northeastern China, including many complete skeletons of Confuciusornis, provide evidence for a fundamental dichotomy in the class Aves that may antedate the temporal occurrence of the Late Jurassic Archaeopteryx. The abundance of Confuciusornis may provide evidence of avian social behavior. Jurassic skeletal remains of an ornithurine bird lend further support to the idea of an early separation of the line that gave rise to modern birds. Chaoyangia, an ornithurine bird from the Early Cretaceous of China, has premaxillary teeth. 相似文献
18.
Wogelius RA Manning PL Barden HE Edwards NP Webb SM Sellers WI Taylor KG Larson PL Dodson P You H Da-qing L Bergmann U 《Science (New York, N.Y.)》2011,333(6049):1622-1626
Well-preserved fossils of pivotal early bird and nonavian theropod species have provided unequivocal evidence for feathers and/or downlike integuments. Recent studies have reconstructed color on the basis of melanosome structure; however, the chemistry of these proposed melanosomes has remained unknown. We applied synchrotron x-ray techniques to several fossil and extant organisms, including Confuciusornis sanctus, in order to map and characterize possible chemical residues of melanin pigments. Results show that trace metals, such as copper, are present in fossils as organometallic compounds most likely derived from original eumelanin. The distribution of these compounds provides a long-lived biomarker of melanin presence and density within a range of fossilized organisms. Metal zoning patterns may be preserved long after melanosome structures have been destroyed. 相似文献
19.
Jones TD Ruben JA Martin LD Kurochkin EN Feduccia A Maderson PF Hillenius WJ Geist NR Alifanov V 《Science (New York, N.Y.)》2000,288(5474):2202-2205
Longisquama insignis was an unusual archosaur from the Late Triassic of central Asia. Along its dorsal axis Longisquama bore a series of paired integumentary appendages that resembled avian feathers in many details, especially in the anatomy of the basal region. The latter is sufficiently similar to the calamus of modern feathers that each probably represents the culmination of virtually identical morphogenetic processes. The exact relationship of Longisquama to birds is uncertain. Nevertheless, we interpret Longisquama's elongate integumentary appendages as nonavian feathers and suggest that they are probably homologous with avian feathers. If so, they antedate the feathers of Archaeopteryx, the first known bird from the Late Jurassic. 相似文献
20.
A primitive enantiornithine bird and the origin of feathers 总被引：2，自引：0，他引：2
A fossil enantiornithine bird, Protopteryx fengningensis gen. et sp. nov., was collected from the Early Cretaceous Yixian Formation of Northern China. It provides fossil evidence of a triosseal canal in early birds. The manus and the alular digit are long, as in Archaeopteryx and Confuciusornis, but are relatively short in other enantiornithines. The alula or bastard wing is attached to an unreduced alular digit. The two central tail feathers are scalelike without branching. This type of feather may suggest that modern feathers evolved through the following stages: (i) elongated scale, (ii) central shaft, (iii) barbs, and finally (iv) barbules and barbicel. 相似文献