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Early mineralization is widely regarded as an important factor in exceptionally preserved soft tissue in the fossil record. However, there is a race against time between soft tissue destruction and the mineralization process. Dehydration of terrestrial animal carcasses may gain valuable time in that race. The decay of collagen, the dominant protein in most animals, is poorly understood and consequently difficult to assess in fossils because of complex changes following the death of an animal. We analysed the ultrastructure of collagen from decomposed dolphin, python and turtle tissue, which had subsequently been air-dried, using scanning and transmission electron microscopy and small angle X-ray scattering. Despite severe exposure of the dolphin tissue to decay and dehydration, many collagen fibres maintained their structural integrity, showing little degradation. Fibril shrinkage as indicated by the characteristic D-banding of collagen was quite small in all the dehydrated tissue studied compared to native tissue. Thus, with respect to the first stage of preservation the structural identity of the tissue is retained. However, the ephemeral benefits of dehydration must be transcribed to long-term geological survival — usually by mineralization. This would require re-hydration of the tissue so that decay by bacteria and release of minerals occur or the tissue is exposed to water-borne minerals that permeate the tissue. Re-hydrating the dehydrated tissue showed minimal structural loss. In nature seasonal dry periods may have a devastating effect on animals often accounting for mass mortalities and unlikelihood of mineralization at the time (either authigenic mineralization or permineralization). However, with the return of the seasonal summer rains and floodwaters often rich in minerals, re-hydration of the dried animal carcasses or parts may present, as we have shown, a viable second chance for mineralization and long term survival of informative tissue structure. Briefly mentioned in comparison is keratin, which has a higher natural propensity for survival compared to collagen.

Fibrillin-rich microfibrils are the major structural components of the extracellular matrix that provide elasticity in a majority of connective tissues. The basis of elastic properties lies in the organization of fibrillin molecules, which, unfortunately, is still poorly understood. An X-ray diffraction study of hydrated fibrillin-rich microfibrils from zonular filaments has been conducted to give an insight into the molecular structure of microfibrils in intact tissue. A series of measurements was taken during controlled tissue extension to observe alterations in the lateral packing of microfibrils. Computer-generated simulated patterns were used to fit the experimental X-ray scattering data and to obtain the fibril diameter and lateral distance between the fibrils. The results suggest a nonlinear correlation between external strain and decrease in fibril diameter and lateral spacing. This was accompanied by a nonlinear increase in axial periodicity and a structure with a 160-nm periodicity, which is reported here for the first time using X-ray diffraction. These changes may reflect the unraveling of fibrillin from the complex folded arrangement into a linear structure. This finding supports a pleating model where fibrillin molecules are highly folded within the microfibrils; more importantly, the connection is made between the interaction of individual microfibrils and the change in their suprafibrillar coherent organization during extension. We suggest that the intermediate states observed in our study reflect sequential unfolding of fibrillin and can explain the process of its reversible unraveling.