Exceptionally preserved fossil feathers and feather-like integumentary structures provide valuable insights into the early evolution of feathers and flight, but taphonomic biases often make interpretations at the microstructural and ultrastructural levels ambiguous. Maturation experiments have been demonstrated to be useful for investigating the taphonomic alterations of soft tissues, including feathers, during diagenesis. However, experimentally matured feathers resembling fossil feathers preserving keratinous matrix have not yet been obtained. Here we employ experimental maturation to obtain feathers corresponding to different degradation stages, and compare these matured feathers with untreated feathers and fossil feathers at the macroscopic, microstructural, and ultrastructural levels. Results show that several features of thermally matured feathers are similar to those found in fossil feathers. The fusion of barbules that occurred in thermally matured feathers suggests that such a process could occur during diagenesis, making barbules difficult to identify in fossil feathers. Under the most extreme experimental condition, the keratinous matrix can partially survive when the whole feather is turned into ash-like remains and many melanosomes are exposed. Moreover, our results show that the keratinous matrix immediately surrounding melanosomes appears to be more resistant to degradation than the unpigmented keratinous matrix, supporting the hypothesis that melanin can act as a fixative agent to prevent the degradation of keratin.

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