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Egg taphonomy
Egg taphonomy is the study of the decomposition and fossilization of eggs. The processes of egg taphonomy begin when the egg either hatches or dies. Eggshell fragments are robust and can often travel great distances before burial. More complete egg specimens gradually begin to fill with sediment, which hardens as minerals precipitate out of water percolating through pores or cracks in the shell. Throughout the fossilization process the calcium carbonate composing the eggshell generally remains unchanged, allowing scientists to study its original structure. However, egg fossils buried under sediments at great depth can be subjected to heat, pressure and chemical processes that can alter the structure of its shell through a process called diagenesis.
==Laying and burial==
The formation of fossil eggs begins with the original egg itself. Not all eggs that end up fossilizing experience the death of their embryo beforehand. Even eggs that successfully hatch can fossilize. In fact, not only is this possible it's actually common. Many fossil dinosaur eggs are preserved with their tops broken open by the escaping hatchling. Of course not all open fossil eggs made it to a happy ending. Some contain fossil feces (known formally as coprolites) left by the larvae of scavenging insects like flies.〔 Dinosaur eggs may have been the victim of the same causes of mortality suffered by modern bird and reptile eggs, like asphyxiation due to overly deep burial, congenital health problems, dehydration, disease, drowning, and inimical temperatures. After hatching or death the processes of decomposition and/or preservation begin. As noted, insects can be among the first scavengers of a dead egg, but deeply buried specimens may not be accessible to them and will be decomposed solely by bacteria and fungi.〔 Whether or not hatching was successful, water and wind would fill the egg with sediment through any large openings.〔 Not all fossil egg specimens are of complete specimens, though. According to egg paleontologist Kenneth Carpenter, individual pieces of eggshell are much more robust than the entire egg. This strength comes from the organic matter that cements the eggshell's calcite crystals together. Simple experiments have demonstrated that under certain conditions eggshell can be transported for 68 kilometers or 42 miles with little loss of size. The durability of eggshell under transport means that pieces of fossil eggshell aren't necessarily discovered in deposits geographically close to the nest they originated from.〔
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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