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A new enantiornithine, Musivavis amabilis n. gen. n. sp., is reported from the Lower Cretaceous Jehol Biota in western Liaoning, China. The new taxon is similar to the bohaiornithids in the robust subconical teeth, bluntly expanded omal ends of the furcula, caudolaterally oriented lateral trabeculae with triangular distal ends of the sternum, and a robust second pedal digit. Yet it differs from members of Bohaiornithidae in several features recalling other enantiornithine lineages, such as the acuminate rostral ramus of maxilla, the shape of the coracoid lateral margin, the presence of craniolateral processes on the sternum, the proportions of the manual phalanges, and the unspecialized third pedal ungual phalanx. A comprehensive phylogenetic analysis of Mesozoic birds shows that homoplasy significantly affects the reconstruction of enantiornithine relationships. When all phylogenetic characters are considered of equal weight, Musivavis is reconstructed in a lineage related to a radiation of large-bodied enantiornithines including Bohaiornithidae and Pengornithidae. Alternative scenarios based on progressive downweighting of the homoplastic characters support more basal placements of the pengornithids among Enantiornithes, but do not alter the affinity of Musivavis as a member of the “bohaiornithid-grade” group.
It has been amply demonstrated that trawl fishing affects overall biomass, size and species structure of demersal fish communities, and an increasing number of studies are proving that this could have even greater unexpected effects on biological diversity. The aims of this study are: (1) to examine the temporal trends of several ecological diversity indices for middle-slope communities in specific locations within the Sardinian seas, which have been recently subject to increasing fishing capacity; and (2) to simulate the Shannon's entropy (H′) temporal trend, using a multiple linear regression, in order to investigate about the relationships between fishing effort and species diversity. The data come from 11 MEDITS trawl surveys (1994 to 2004). Temporal trends in fishing effort were analysed and ecological diversity indices were measured. Analysis was conducted for four areas (NW, NE, SE, SSW). Significant variations over time in both fishing pressure and ecological diversity indices were found for the southern zones. More precisely, the SE zone showed an increase in fishing effort (+120% in 2004), and a decrease of Shannon–Weiner's diversity. The SSW zone exhibited a 22.6% increase of fishing effort and a decrease of species richness. The best model of H′ incorporates species richness and fishing effort expressed as number of boats per trawling area. Our results seem to indicate that fishing pressure affected the species richness and the abundance of middle-slope species and that variation in ecological diversity indices differed with different levels of fishing effort.
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