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Egg paleopathology
Egg paleopathology is the study of evidence for illness, injury, and deformity in fossilized eggs. A variety of pathological conditions afflicting eggs have been documented in the fossil record. Examples include eggshell of abnormal thickness and fossil eggs with multiple layers of eggshell. The identification of egg paleopathologies is complicated by the fact that even healthy eggs can be modified during or after fossilization. Paleontologists can use techniques like cathodoluminescence or thin sectioning to identify true paleopathologies in fossil eggs. Despite the diversity of paleopathologies known from fossil eggs, the vast majority of conditions known to afflict modern eggs have not yet been seen among fossils.
==Identification==
Differences in preservation and diagenesis make it difficult to confidently identify eggshell pathologies in the fossil record. Multilayered eggshell identification can be complicated if the secondary eggshell is disconnected from the original. When this happens the two shells can vary in structure and may even be mistaken as coming from different types of eggs.〔 Stacked eggshells from collapsed or compressed eggs may resemble multilayered eggshells but in thin cross-sections viewed under a microscope the stacked shell will have mammilae facing opposite directions whereas egg shells that developed in layers on top of each other will have mammilae facing the same direction.〔 Also, in stacked shells the layer separating the shells will resemble the sediment surrounding the fossil and in multilayer the layer between shells will resemble the primary shell more than the surrounding sediment.〔
Cathodoluminescence can be used to distinguish pathological egg shell from egg shell that has been altered diagenetically. Rigid egg shells, except in turtles, are composed of calcite. Since calcitic and aragonitic structures do not luminesce, signs of luminescence point to alterations to the chemical composition or structure of the shell. Magnesium-Calcite is sometimes replaced by Manganese-Calcite, which luminesces bright red-orange or yellow orange. In multilayer eggs the shells will appear the same color, but the shell membrane between them tends to be replaced by manganese-calcite that luminseces bright orange. Manganese is the primary instigator of luminescence whereas iron hinders it.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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