Dinos non aviens de Chine

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Posté par Markvantomme il y a 18 ans

Xu & Norell (2006) Non-Avian dinosaur fossils from the Lower Cretaceous Jehol Group of western Liaoning, China. GEOLOGICAL JOURNAL 41: 419–437

Over the past 10 years, numerous dinosaur specimens covering several major dinosaurian clades have been recovered from theLower Cretaceous Jehol Group of western Liaoning. Among ornithischians from the Jehol Group, ornithopod fossils shed new light on the evolution of this largest ornithischian group; ankylosaurian discoveries add morphological diversity relevant to the highly specialized ankylosaurian body-plan and ceratopsian occurrences offer a chance to study patterns of morphological change at the base of the Ceratopsia. The most signiﬁcant discoveries are exceptionally well-preserved theropod specimens covering most major coelurosaurian groups. Most theropod taxa from the Jehol Biota are the earliest, most basal members of
coelurosaurian sub-clades and provide substantial new information important for the reconstruction of coelurosaurian
phylogeny and understanding the character evolution. The examination of character distributions along the coelurosaurian lineages reveals that the major structural modiﬁcations seen in birds were acquired sequentially and hierarchically early in coelurosaurian evolution. Most signiﬁcantly, the Liaoning theropod discoveries advanced our understanding of two longdebated evolutionary issues: the origin and early evolution of feathers and the origin of avian ﬂight. The known distribution of the feather-like integumentary structures and true feathers along the coelurosaurian lineages suggests that: (1) simple,
ﬁlamentous integuments represent a primitive morph in feather evolution; (2) pennaceous feathers evolved early in maniraptoran evolution; and (3) feathers with aerodynamic features originated before the origin of birds. The presence of ﬂight feathers on the metatarsus represents a new morph that is not known previously, but it has implications for understanding the origin of avian ﬂight. The discovery of four-winged dinosaurs was suggested to provide strong evidence supporting the ‘tree-down' hypothesis for the origin of avian ﬂight, though in-depth analysis and more data are needed to conﬁrm this. A brief analysis of the fossil preservation and faunal composition reveals several interesting characteristics: (1) Volcanic activity might have contributed to the exceptional preservation of dinosaurian skeletons and in particular their soft tissues; (2) Different from most other dinosaur faunas, the Jehol dinosaur fauna has a low ornithischian speciﬁc diversity relative to a high theropod speciﬁc diversity; and (3)
the Liaoning theropods show a strong tendency toward secondary herbivory. The faunal composition suggests a complex biogeographic history for this fauna and provides negative evidence for the hypothesis that eastern Asia was isolated from the Middle Jurassic through late Early Cretaceous times.

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