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A megabias, or a taphonomic megabias is a large scale pattern in the quality of the fossil record that affects paleobiologic analysis at provincial to global levels and at timescales usually exceeding ten million years. It can result from major shifts in intrinsic and extrinsic properties of organisms, including morphology and behaviour in relation to other organisms, or shifts in the global environment, which can cause secular or long-term cyclic changes in preservation.〔 ==Introduction== The fossil record exhibits bias at many different levels. At the most basic level, there is a global bias towards biomineralizing organisms, because biomineralized body parts are more resistant to decay and degradation. Due to the principle of uniformitarianism, there is a basic assumption in geology that the formation of rocks has occurred by the same naturalistic processes throughout history, and thus that the reach of such biases remains stable over time. A megabias is a direct contradiction of this, whereby changes occur in large scale paleobiologic patterns. This includes * Changes in diversity and community structure over tens of millions of years * Variation in the quality of the fossil record between mass and background extinction times * Variation among different climate states, biogeographic provinces, and tectonic settings. It is generally assumed that the quality of the fossil record decreases globally and across all taxa with increasing age, because more time is available for the diagenesis and destruction of both fossils and enclosing rocks, and thus the term "megabias" is usually used to refer to global trends in preservation. However it has been noted that the fossil record of some taxa actually ''improves'' with greater age.〔 Examples such as this, and other related paleobiological trends, clearly indicate the action of a megabias, but only within one particular taxon. Hence, it is necessary to define four classes of megabias related to the reach of the bias, first defined by Kowalewski and Flessa. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Megabias」の詳細全文を読む スポンサード リンク
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