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Shared behavioural, morphological and physiological characteristics are indicative of the evolution of extant birds from nonavian maniraptoran dinosaurs. One such shared character is the presence of uncinate processes and respiratory structures in extant birds. Recent research has suggested a respiratory role for these processes found in oviraptorid and dromaeosaurid dinosaurs. By measuring the geometry of fossil rib cage morphology, we demonstrate that the mechanical advantage, conferred by uncinate processes, for movements of the ribs in the oviraptorid theropod dinosaur, Citipati osmolskae, basal avialan species Zhongjianornis yangi, Confuciusornis sanctus and the more derived ornithurine Yixianornis grabaui, is of the same magnitude as found in extant birds. These skeletal characteristics provide further evidence of a flow-through respiratory system in nonavian theropod dinosaurs and basal avialans, and indicate that uncinate processes are a key adaptation facilitating the ventilation of a lung air sac system that diverged earlier than extant birds.

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Primitive ornithomimids, a ubiquitous group of specialized Cretaceous dinosaurs nested within a clade of predominantly carnivorous theropods, are known to have had teeth, whereas derived ornithomimids had an edentulous beak, which has prompted speculation about their dietary habits. Here we describe two new ornithomimid specimens in which soft-tissue structures of the beak have been preserved. These creatures probably used their beaks to strain food sediment in an aqueous environment, rather than for predation on large animals.

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Non-avian theropod dinosaurs with preserved integumentary coverings are becoming more common; but apart from the multiple specimens of Caudipteryx, which have true feathers, animals that are reasonably complete and entirely articulated that show these structures in relation to the body have not been reported. Here we report on an enigmatic small theropod dinosaur that is covered with filamentous feather-like structures over its entire body.

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Despite the discoveries of well-preserved Mesozoic birds, a key part of avian evolution, close to the radiation of all living birds (Aves), remains poorly represented. Here we report on a new taxon from the Late Cretaceous locality of Ukhaa Tolgod, Mongolia, that offers insight into this critically unsampled period. Apsaravis and the controversial alvarezsaurids are the only avialan taxa known from the continental deposits at Ukhaa Tolgod, which have produced hundreds of fossil mammals, lizards and other small dinosaurs. The new taxon, Apsaravis ukhaana, is the best-preserved specimen of a Mesozoic ornithurine bird discovered in over a century. It provides data important for assessing morphological evolution across Avialae, with implications for, first, the monophyly of Enantiornithes and Sauriurae; second, the proposition that the Mesozoic sister taxa of extant birds, as part of an 'ecological bottleneck', inhabited exclusively near-shore and marine environments; and third, the evolution of flight after its origin.

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An embryonic skeleton of a nonavian theropod dinosaur was found preserved in an egg from Upper Cretaceous rocks in the Gobi Desert of Mongolia. Cranial features identify the embryo as a member of Oviraptoridae. Two embryo-sized skulls of dromaeosaurids, similar to that of Velociraptor, were also recovered in the nest. The eggshell microstructure is similar to that of ratite birds and is of a type common in the Djadokhta Formation at the Flaming Cliffs (Bayn Dzak). Discovery of a nest of such eggs at the Flaming Cliffs in 1923, beneath the Oviraptor philoceratops holotype, suggests that this dinosaur may have been a brooding adult.

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The fossil record offers the only direct evidence of extinct life and thus has figured prominently in considerations of evolutionary patterns. But the incomplete nature of the fossil record has also been emphasized in arguments that fossils play only a secondary role in the recovery of phylogenetic histories based on extant taxa. Although these criticisms recently have been countered, there is no general understanding of the correspondence between the fossil record and phylogeny. An empirical survey of recently published studies suggests no basis for assuming that the stratigraphic occurrence of fossils always provides a precise reflection of phylogeny. Nevertheless, our survey of a sample of taxa shows a tendency for positive correlation between age and clade rank and, hence, a degree of correspondence between phylogenetic pattern and the paleontologic record.

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The purpose of the present study was to examine the differences between cardiac steroids that might underlie the variations in toxic/therapeutic ratios that have been reported to occur in vitro as well as in vivo. We used Na(+)-sensitive microelectrodes to measure changes in intracellular Na+ activity (aiNa) associated with positive inotropic and toxic effects of acetylstrophanthidin (AS) and a semisynthetic agent, actodigin. Measurements of aiNa, twitch tension and transmembrane potential were made in sheep Purkinje fibers stimulated at 0.03, 1 and 2 Hz. Ca(+)+i overload toxicity was indicated by the presence of transient depolarizations (TD). The following results were obtained: 1) at a stimulation frequency of 1 Hz, aiNa was significantly higher at peak tension with AS (13.6 +/- 1.1 mM) than with actodigin (11.0 +/- 0.4 mM, P less than .01), yet TD occurred at the same aiNa (10.9 +/- 0.7 vs. 11.9 +/- 0.7 mM, respectively, N.S.); 2) at frequencies of 1 to 2 Hz, aiNa was lower when TD occurred (10.4 +/- 0.9 mM at 2 Hz) than at peak tension (12.1 +/- 0.8 mM, P less than .05) during exposure to AS, whereas aiNa was the same at peak tension (10.6 +/- 1.1 mM) and when TD occurred (10.5 +/- 1.1 mM, N.S.) during exposure to actodigin; 3) the degree of positive inotropy at a high stimulation frequency (2 Hz) was significantly greater with actodigin (about 12-fold increase in force compared to control) than with AS (about 6-fold increase in force).(ABSTRACT TRUNCATED AT 250 WORDS)

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Interstitial cells of Cajal (ICC) have been suggested as pacemaker cells in the gastrointestinal tract. A method was developed to isolate ICC from the slow-wave pacemaker region of the canine proximal colon. These cells were identified under phase-contrast microscopy, and their identity was verified by comparing their ultrastructure with the morphology of ICC in situ. Patch-clamp experiments demonstrated that these cells are excitable; voltage-dependent inward and outward currents were elicited by depolarization. Inward current transients were identified as calcium currents. A portion of the outward current appears to be due to Ca2+-activated K channels commonly expressed in these cells. ICC were also spontaneously active, generating electrical depolarizations similar in waveform to slow-wave events of intact colonic muscles. These findings are consistent with the hypothesis that ICC initiate rhythmicity in the colon.

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