Early Cretaceous Bird Research Articles

Leg feathers in an Early Cretaceous bird

Here we describe a fossil of an enantiornithine bird from the Early Cretaceous period in China that has substantial plumage feathers attached to its upper leg (tibiotarsus). The discovery could be important in view of the relative length and aerodynamic features of these leg feathers compared with those of the small 'four-winged' gliding dinosaur Microraptor and of the earliest known bird, Archaeopteryx. They may be remnants of earlier long, aerodynamic leg feathers, in keeping with the hypothesis that birds went through a four-winged stage during the evolution of flight.

The birds from Las Hoyas.

Information on the first steps of the avian evolutionary history has dramatically increased during the last few years. The fossil record provides a general view of the morphological changes of the avian flight apparatus from nonvolant ancestors (non-avian theropod dinosaurs) to the first derived fliers of the Early Cretaceous. The Las Hoyas bird record includes three genera: Iberomesornis, Concornis and Eoalulavis. This fossil material has yielded information about the early avian evolutionary history. These Early Cretaceous birds (some 120 Myr old) had a wingbeat cycle and breathing devices similar to those of extant birds. The function of the rectricial fan was also similar. In the evolutionary transition from cursorial ancestors to derived fliers it is possible to verify a trend to increase lift. Primitive wing aspect ratio morphotypes were elliptical ones, other derived morphotypes appeared, for example, in the Neornithes (extant birds). Some primitive fliers, like the Las Hoyas genus Eoalulavis, had an alula (feathers attached to the first digit of the hand) similar to that of present day birds, indicating braking and manoeuvring skills similar to those of their extant relatives. Primitive avian life habits are poorly understood. Some evidence from the Las Hoyas bird record indicates that Early Cretaceous birds were present in the trophic chains.

A new and primitive enantiornithine bird from the Early Cretaceous of China

ABSTRACT A new Early Cretaceous enantiornithine bird, Eocathayornis walkeri, gen. et sp. nov. is reported from Liaoning, northeast China. It is about the size of Cathayornis but is more primitive. Teeth are present on the jaws. Claws are retained on three wing digits, but that of the minor digit is reduced. The width of the radius is nearly three-fourths that of the ulna. The sternum is relatively short, with a pair of long caudo-lateral processes and a low and caudally distributed keel. The coracoid is strut-like and caudally concave, typical of enantiornithine birds. The advanced features of the scapula and the wing suggest a powerful flapping flight capability. This bird is referred to the family Cathayornidae based on a few shared derived characters with Cathayornis.

Largest bird from the Early Cretaceous and its implications for the earliest avian ecological diversification.

With only one known exception, early Cretaceous birds were smaller than their closest theropod dinosaur relatives. Here we report on a new bird from the Early Cretaceous feathered-dinosaur-bearing continental deposits of Liaoning, northeast China, which is not only larger than Archaeopteryx but is nearly twice as large as the basal dromaeosaur Microraptor. The new taxon, Sapeornis chaoyangensis gen. et sp. nov., has a more basal phylogenetic position than all other birds except for Archaeopteryx. Its exceptionally long forelimbs, well-developed deltoid crest of the humerus, proximally fused metacarpals, relatively short hindlimbs and short pygo-style indicate powerful soaring capability and further suggest that by the Early Cretaceous ecological diversification of early birds was greater than previously assumed. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00114-001-0276-9.

Liaoxiornis delicatus gen. et sp. nov., the smallest Mesozoic bird

Recently, a very small and complete bird specimen was collected from the Confuciu-sorn/s-bearing Yixian Formation. This finding represents a new kind of Mesozoic bird, named Liaoxiornis delicatus. It is characterized by a short skull with teeth, a long neck and a very small sternum with only posterior process; the humeral head is not internally curved, and the hindlimbs are longer than the forelimbs. Liaoxiornis delicatus is not only much smaller than Confuciusornis, but also smaller than Cathayornis and other early Cretaceous birds. It is the smallest bird known from Mesozoic deposit. Liaoxiornis provides new evidence indicating that the early adaptive radiation of birds is complicated.

The contractile properties of the M. supracoracoideus In the pigeon and starling: a case for long-axis rotation of the humerus

Wing upstroke in birds capable of powered flight is kinematically the most complicated phase of the wingbeat cycle. The M. supracoracoideus (SC), generally considered to be the primary elevator of the wing, is a muscle with a highly derived but stereotyped morphology in modern flying birds. The contractile portion of the SC arises from a ventral sternum, but its tendon of insertion courses above the glenohumeral joint to insert on the dorsal surface of the humerus. To clarify the role of the SC during wing upstroke, we studied its contractile and mechanical properties in European starlings (Sturnus vulgaris) and pigeons (Columba livia), two birds with contrasting flight styles. We made in situ measurements of isometric forces of humeral elevation and humeral rotation and, in addition, measured the extent of unrestrained humeral excursion during stimulation of the muscle nerve. We also generated passive and active length-force curves for the SC of each species. Stimulation of the SC at humeral joint angles of elevation/depression and protraction/retraction coincident with the downstroke-upstroke transition and mid-upstroke produced substantially higher forces of long-axis rotation than elevation. When the humerus was allowed to move (rotate/elevate) during stimulation, we observed rotation about its longitudinal axis of up to 70-80 degrees , but humeral elevations of only 40-60 degrees above the horizontal (as measured in lateral view). In the active length-force experiments, we measured mean (+/-s.d.) maximal tetanic forces of 6.5+/-1.2 N for starlings (N=4) and 39.4+/-6.2 N for pigeons (N=6), unexpectedly high forces approximately 10 times body weight. The working range of the SC in both species corresponds to the ascending limb (but not the plateau) of the active length-force curve. The potential for greatest active force is high on the ascending limb at joint angles coincident with the downstroke-upstroke transition, a time when the humerus is depressed below the horizontal and rotated forward maximally. As the SC shortens to counterrotate and elevate the humerus during early upstroke, the potential for active force at shorter lengths declines at a relatively rapid rate. These findings reveal that the primary role of the SC is to impart a high-velocity rotation of the humerus about its longitudinal axis, which rapidly elevates the distal wing. This rapid twisting of the humerus is responsible for positioning the forearm and hand so that their subsequent extension orients the outstretched wing in the parasagittal plane appropriate for the subsequent downstroke. We propose that, at the downstroke-upstroke transition, variable levels of co-contraction of the M. pectoralis and SC interact to provide a level of kinematic control at the shoulder that would not be possible were the two antagonists to work independently. The lack of a morphologically derived SC in Late Jurassic and Early Cretaceous birds precluded a high-velocity recovery stroke which undoubtedly limited powered flight in these forms. Subsequent evolution of the derived SC capable of imparting a large rotational force to the humerus about its longitudinal axis was an important step in the evolution of the wing upstroke and in the ability to supinate (circumflex) the manus in early upstroke, a movement fundamental to reducing air resistance during the recovery stroke.

Early Late Cretaceous birds from Saskatchewan, Canada: the oldest diverse avifauna known from North America

ABSTRACT Five taxa of fossil birds comprising at least 17 individuals have been discovered in a Cenomanian (early Late Cretaceous) nearshore marine deposit along the Carrot River, near the Pasquia Hills of Saskatchewan, Canada. More than a hundred fossils, all from a single locality, constitute the oldest and most diverse avifauna from the Cretaceous of North America. Four species represent the earliest known North American Ornithurae, two of them new species of the baptornithid Pasquiaornis, n. gen. (Hesperornithiformes), and the other two referred to the ichthyornithid Ichthyornis (Ichthyornithiformes). Pasquiaornis is more primitive than Baptornis, and its humérus and femur show resemblances to those of flying birds. A presumed enantiornithine is also present.

Early Adaptive Radiation of Birds: Evidence from Fossils from Northeastern China

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.

An Early Cretaceous bird from Spain and its implications for the evolution of avian flight

AVIAN flight is one of the most remarkable achievements of vertebrate evolution, yet there is little evidence of its early phases. Specimens of Archaeopteryx shed important (albeit controversial) light on this evolutionary phenomenon, but the large morphological (and almost certainly functional) gap between Archaeopteryx and modern avians remained virtually empty until recently. Here we report a new, exquisitely preserved, bird from the Lower Cretaceous Konservat-Lagerstatte of Las Hoyas (Cuenca, Spain) which provides evidence for the oldest known alula (bastard wing). Crustacean remains found inside its belly also provide the oldest direct evidence of feeding habits in birds. The new specimen has numerous synapomorphies with the Enantiornithes, but its unique sternal morphology, along with other autopomorphies in the furcula and vertebral centra, support the recognition of a new enantiornithine taxon, Eoalulavishoyasi. The combination in Eoalulavis of a decisive aerodynamic feature, such as the alula, with the basic structures of the modern flight apparatus indicates that as early as 115 million years ago, birds had evolved a sophisticated structural system that enabled them to fly at low speeds and to attain high manoeuvrability.

A Lower Cretaceous enantiornithine bird from the Ordos Basin of Inner Mongolia, People's Republic of China

The discovery of an Early Cretaceous bird from the Ordos Basin of Inner Mongolia (People's Republic of China) is reported. The specimen, collected by the Dinosaur Project (China – Canada – Alberta – Ex Terra) Expedition of 1990, includes scapulocoracoids, humeri, radii, ulnae and metacarpals. It is referred to the Enantiornithes.

Braincase ofEnaliornis, an Early Cretaceous bird from England

ABSTRACT The braincase of the Early Cretaceous bird Enaliornis is indicative of a primitive avian brain with a relatively large medulla oblongata, a small cerebellum, small cerebral hemispheres broadly separated from the labyrinth, and a strong basilordotic bend of the whole brain, the latter being characteristic of an airencephalic skull. The reduction of the dorsal pneumatic recess, the large size of the auricular fossa, and possibly the lack of interfoliar ridges on the roof of the cerebellar fossa suggest diving habits and thus support the association of the braincases with the type tarsometatarsus of Enaliornis. The braincase of Enaliornis is most similar to those of Hesperornis, Phaethon, Diomedeidae and Fregata. Most of the similarities to these taxa are primitive for birds.

REPTILIAN PHYSIOLOGY AND THE FLIGHT CAPACITY OF ARCHAEOPTERYX.

Current scenarios frequently interpret the Late Jurassic bird Archaeopteryx as having had an avian-type physiology and as having been capable of flapping flight, but only from "the trees downward." It putatively lacked capacity for takeoff and powered flight from the ground upward. Data from extant reptiles indicate that if Archaeopteryx were physiologically reptilian, it would have been capable of ground upward takeoff from a standstill, as well as "trees downward" powered flight. This conclusion is based largely on a previously unrecognized attribute of locomotory (skeletal) muscle in a variety of extant reptiles: During "burst-level" activity, major locomotory muscles of a number of active terrestrial taxa generate at least twice the power (watts kg-1 muscle tissue) as those of birds and mammals. Reptilian physiological status also helps resolve the apparently uneven development of various flight support structures in Archaeopteryx (e.g., well-developed flight features but relatively unspecialized pectoral girdle, supracoracoideus muscles, etc.). Endothermy and capacity for longer-distance powered flight probably evolved only in Early Cretaceous birds, which were the first birds to have a keeled sternum, strap-like coracoid, and hypocleidium-bearing furcula.

Unusual Early Cretaceous birds from Spain

The Neocomian Spanish outcrops of Montsec (province of Lerida) and the new one of Las Hoyas (province of Cuenca) have yielded several avian remains in the last few years. Several isolated feathers have been reported from Montsec, and a specimen of some feathered wing bones has recently been found. Las Hoyas has yielded an isolated feather and a nearly articulated small fossil bird that lacks the skull. This new specimen, reported here, presents a combination of derived (strut-like coracoids, pygostyle) and primitive (pelvic girdle, sacrum, hind limb) character states. If one considers Archaeopteryx, Ornithurae and the new Spanish fossil bird, it seems clear that the latter taxon is the sister group of Ornithurae (extant birds and all other fossil birds that are closer to recent forms than is Archaeopteryx).

A true carinate bird from lower Cretaceous deposits in Mongolia and other evidence of early Cretaceous birds in Asia

A partial, associated skeleton with feather impressions of a bird from early Cretaceous (Neocomian) deposits in Mongolia constitutes a new family and order (Ambiortidae, Ambiortiformes). The specimen presents a mosaic of archaic and specialised characters within the Class Aves and shows that advanced carinate birds existed some 10 to 12 million years after Archaeopteryx, lending tentative support to the idea that Archaeopteryx may not be representative of the state of avian evolution in the late Jurassic. The new specimen and numerous feather impressions from other early Cretaceous localities in Mongolia and the Soviet Union, indicate that birds were probably common in early Cretaceous biotas.