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751.
The recently reported Jeholornis represents the only known bird with a complete long skeletal tail except for Archaeopteryx. Two newly discovered specimens referable to Jeholornis provide some important new information about its anatomy. The tail of Jeholornis is much longer than that of Archaeopteryx and comprises a maximum of 27 caudal vertebrae compared with only 23 in Archaeopteryx. More interestingly, the tail feathers are shaped more like those of dromaeosaurs than those of Archaeopteryx. We conclude that the common ancestor of birds must have a more primitive tail than that in Archaeopteryx, confirming the side branch position of Archaeopteryx in the early avian evolution. The synsacrum is composed of six sacrals, representing a transitional stage between Archaeopteryx and more advanced birds. The scapula of Jeholornis has a dorso-laterally exposed glenoid facet, and the coracoid has a supracoracoid foramen. The presence of a pair of fenestrae
in the sternum of Jeholornis has further implications for the air-sac system in early birds.
Electronic Supplementary Material The online version of this article (doi: contains supplementary material, which is available to authorized users. 相似文献
752.
Apesteguía S 《Die Naturwissenschaften》2004,91(10):493-497
Ornithischian and theropod dinosaurs were morphologically diverse during the Cretaceous. In contrast, sauropods were relatively more conservative. The anatomy of Bonitasaura salgadoi, a new 9-m titanosaurian sauropod from Upper Cretaceous beds of Patagonia, suggests that sauropod anatomical diversity would have included unexpected items. Its unusual, rectangular lower jaw possesses narrow, anteriorly restricted teeth and shows evidence of a sharp keratinous sheath over the non-dentigerous region that probably worked to guillotine plant material. This discovery definitely demonstrates that titanosaurs acquired a mandibular configuration similar to that of some basal diplodocoids, as had already been suggested by the lower jaw of the controversial genus Antarctosaurus. This oral configuration, plus the beak-like structure and the skull shape, resemble some traits more commonly seen in Laurasian ornithischians, mostly unexpressed in southern continents. A high sauropod morphological diversity seems to be in agreement with the poorly represented ornithischian clades of the southern hemisphere.Communicated by G. Mayr 相似文献
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Animals assess the fighting ability of conspecifics either by engaging in aggressive interactions or observing contests between others. However, whether individuals assess physical prowess outside the context of aggressive interactions remains unknown. We examined whether male green swordtails (Xiphophorus helleri) extract information about the fighting ability of solitary individuals via observation and whether acquiring such information elicits behavioral modifications. Contests preceded by mutual visual assessment were significantly shorter than fights where only one or neither of the two individuals was informed in advance. Focal animals initiated aggressive behavior more often against larger opponents only after previewing their adversary, indicating that swordtails can extract information about relative body size from watching solitary conspecifics. When a fighting disadvantage is perceived, observers adopt tactics that increase their probability of winning the contest. 相似文献
755.
Unai?IriarteEmail author Jon?I?aki?álvarez-Uriarte Rubén?López-Fonseca Juan?Ramón?González-Velasco 《Environmental Chemistry Letters》2003,1(1):57-61
The relatively recent discovery of disinfection by-products has driven the main regulatory organisms to set maximum contaminant
levels for certain substances in drinking water. Trihalomethanes can be deemed as the most important group of by-products
in chlorinated surface waters. The present work has focused on trihalomethane formation in a full-scale water treatment plant.
We studied the effect of several factors, including ozonation, on trihalomethane levels in chlorinated treated water. The
treatment scheme also includes an ozonation step.
Electronic Publication 相似文献
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The movement of animals in groups is widespread in nature. Understanding this phenomenon presents an important problem in ecology with many applications that range from conservation to robotics. Underlying all group movements are interactions between individual animals and it is therefore crucial to understand the mechanisms of this social behaviour. To date, despite promising methodological developments, there are few applications to data of practical statistical techniques that inferentially investigate the extent and nature of social interactions in group movement. We address this gap by demonstrating the usefulness of a Hidden Markov Model approach to characterise individual-level social movement in published trajectory data on three-spined stickleback shoals (Gasterosteus aculeatus) and novel data on guppy shoals (Poecilia reticulata). With these models, we formally test for speed-mediated social interactions and verify that they are present. We further characterise this inferred social behaviour and find that despite the substantial shoal-level differences in movement dynamics between species, it is qualitatively similar in guppies and sticklebacks. It is intermittent, occurring in varying numbers of individuals at different time points. The speeds of interacting fish follow a bimodal distribution, indicating that they are either stationary or move at a preferred mean speed, and social fish with more social neighbours move at higher speeds, on average. Our findings and methodology present steps towards characterising social behaviour in animal groups. 相似文献