Carpometacarpus

About: Carpometacarpus is a research topic. Over the lifetime, 58 publications have been published within this topic receiving 1542 citations.

The origin and early evolution of birds

Abstract: Birds evolved from and are phylogenetically recognized as members of the theropod dinosaurs; their first known member is the Late Jurassic Archaeopteryx, now represented by seven skeletons and a feather, and their closest known non-avian relatives are the dromaeosaurid theropods such as Deinonychus. Bird flight is widely thought to have evolved from the trees down, but Archaeopteryx and its outgroups show no obvious arboreal or tree-climbing characters, and its wing planform and wing loading do not resemble those of gliders. The ancestors of birds were bipedal, terrestrial, agile, cursorial and carnivorous or omnivorous. Apart from a perching foot and some skeletal fusions, a great many characters that are usually considered ‘avian’ (e.g. the furcula, the elongated forearm, the laterally flexing wrist and apparently feathers) evolved in non-avian theropods for reasons unrelated to birds or to flight. Soon after Archaeopteryx, avian features such as the pygostyle, fusion of the carpometacarpus, and elongated curved pedal claws with a reversed, fully descended and opposable hallux, indicate improved flying ability and arboreal habits. In the further evolution of birds, characters related to the flight apparatus phylogenetically preceded those related to the rest of the skeleton and skull. Mesozoic birds are more diverse and numerous than thought previously and the most diverse known group of Cretaceous birds, the Enantiornithes, was not even recognized until 1981. The vast majority of Mesozoic bird groups have no Tertiary records: Enantiornithes, Hesperornithiformes, Ichthyornithiformes and several other lineages disappeared by the end of the Cretaceous. By that time, a few Linnean ‘Orders’ of extant birds had appeared, but none of these taxa belongs to extant ‘families’, and it is not until the Paleocene or (in most cases) the Eocene that the majority of extant bird ‘Orders’ are known in the fossil record. There is no evidence for a major or mass extinction of birds at the end of the Cretaceous, nor for a sudden ‘bottleneck’ in diversity that fostered the early Tertiary origination of living bird ‘Orders’.

A long-tailed, seed-eating bird from the Early Cretaceous of China

Abstract: The lacustrine deposits of the Yixian and Jiufotang Formations in the Early Cretaceous Jehol Group in the western Liaoning area of northeast China are well known for preserving feathered dinosaurs, primitive birds and mammals1,2,3. Here we report a large basal bird, Jeholornis prima gen. et sp. nov., from the Jiufotang Formation. This bird is distinctively different from other known birds of the Early Cretaceous period in retaining a long skeletal tail with unexpected elongated prezygopophyses and chevrons, resembling that of dromaeosaurids4,5,6, providing a further link between birds and non-avian theropods7,8. Despite its basal position in early avian evolution, the advanced features of the pectoral girdle and the carpal trochlea of the carpometacarpus of Jeholornis indicate the capability of powerful flight. The dozens of beautifully preserved ovules of unknown plant taxa in the stomach represents direct evidence for seed-eating adaptation in birds of the Mesozoic era.

Early diversification of birds: Evidence from a new opposite bird

Abstract: A new enantiornithine birdLongipteryx chaoyangensis gen. et sp. nov. is described from the Early Cretaceous Jiufotang Formation in Chaoyang, western Liaoning Province. This new bird is distinguishable from other known enantiornithines in having uncinate processes in ribs, elongate jaws, relatively long wings and short hindlimbs, and metatarsal IV longer than metatarsals II and III. This new bird had probably possessed (i) modern bird-like thorax which provides firm attachment for muscles and indicates powerful and active respiratory ability; (ii) powerful flying ability; (iii) special adaptation for feeding on aquatic preys; and (iv) trochleae of metatarsals I–IV almost on brate heterocoelous. Distal region of sternum with well developed carina and lateral processes. Uncinate processes present but not fused with ribs. At least 6 rows of gastraliae present. Carpometacarpus not completely fused, minor metacarpal longer than major one; second phalanx the same level, an adaptation for perching. The new bird represents a new ecological type different from all known members of Enantiornithes. It shows that enantiornithines had probably originated earlier than the Early Cretaceous, or this group had experienced a rapid radiation right after it first occurred in the early Early Cretaceous.

Functional osteology of the avian wrist and the evolution of flapping flight

Abstract: The avian wrist is extraordinarily adapted for flight. Its intricate osteology is constructed to perform four very different, but extremely important, flight-related functions. (1) Throughout the downstroke, the cuneiform transmits force from the carpometacarpus to the ulna and prevents the manus from hyperpronating. (2) While gliding or maneuvering, the scapholunar interlocks with the carpometacarpus and prevents the manus from supinating. By employing both carpal bones simultaneously birds can lock the manus into place during flight. (3) Throughout the downstroke-upstroke transition, the articular ridge on the distal extremity of the ulna, in conjuction with the cuneiform, guides the manus from the plane of the wing toward the body. (4) During take-off or landing, the upstroke of some heavy birds exhibits a pronounced flick of the manus. The backward component of this flick is produced by reversing the wrist mechanism that enables the manus to rotate toward the body during the early upstroke. The upward component of the flick is generated by mechanical interplay between the ventral ramus of the cuneiform, the ventral ridge of the carpometacarpus, and the ulnocarpo-metacarpal ligament. Without the highly specialized osteology of the wrist it is doubtful that birds would be able to carry out successfully the wing motions associated with flapping flight. Yet in Archaeopteryx, the wrist displays a very different morphology that lacks all the key features found in the modern avian wrist. Therefore, Archaeopteryx was probably incapable of executing the kinematics of modern avian powered flight.

Flightlessness in steamer-ducks (anatidae: tachyeres): its morphological bases and probable evolution.

Abstract: Flightlessness in Tachyeres is caused by wing-loadings in excess of 2.5 g·cm-2 , which result from the large body size and small wing areas of the flightless species. Reduced wing areas of flightless species are related to absolutely shorter remiges, and to relatively or absolutely shortened wing bones, although these reductions differ among species. Reduced lengths of the ulna, radius, and carpometacarpus are associated most strongly with flightlessness. Pectoral muscles and the associated sternal keel are well developed in all species of Tachyeres, largely because of the use of wings in "steaming," an important locomotor behavior. Relative size of these muscles was greatest in largely flighted T. patachonicus; however, sexual dimorphism in wing-loadings results in flightlessness in some males of this species. Proportions in the wing skeleton, intraspecific allometry, and limited data on growth indicate that the relatively short wing bones and remiges of flightless Tachyeres are produced developmentally by a delay in the growth of wing components, and that this heterochrony may underlie, in part, skeletal sexual dimorphism. Increased body size in flightless steamer-ducks is advantageous in territorial defense of food resources and young, and perhaps diving in cold, turbulent water; reductions in wing area probably reflect refinements for wing-assisted locomotion and combat. Flightlessness in steamer-ducks is not related to relaxed predation pressure, but instead was permitted selectively by the year-round habitability of the southern South American coasts. These conditions not only permitted the success of the three flightless species of Tachyeres, but at present may be moving marine populations of T. patachonicus toward flightlessness.