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| Soft tissues may be preserved in fossils by several different processes. Sometimes the actual tissue may be preserved intact because it is embedded within mineralized tissue: for example, collagens are relatively stable and have been extracted from fossil bones. By contrast, other soft tissues may be preserved by mineral replacement of the tissue, on a molecule by molecule basis, producing replicas of muscle tissue such as those known in some fossil fishes from the Santana Formation of Brazil. It seems that both of these processes may have occurred within the therizinosaur eggs, and produced some rather complicated results. | For example, some material which is not attacked by the acetic acid has the characteristic appearance of cartilage, but chemical analysis is essential to determine whether it is actually cartilage or a mineral replica. Some thin layers appear to be composed of mineral replicas of flattened (epithelial ?) cells; one sheet of non-bony material is reminiscent of skin. Skin preservation is already known from adult dinosaurs, especially where the skin has been mummified by drying. This aspect of the therizinosaur eggs is in urgent need of further research. |
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