A new paper:
In recent years, several papers have claimed that soft tissue can preserve within bone matrix of extinct vertebrates, some dating back over 100 million years. Work conducted on specimens from Montana suggested sediment type may influence preservation of original tissues and proteins. An alternative hypothesis is that soft tissue preservation may be linked to the time that a specimen is exposed to the environment prior to burial. The time of exposure can be estimated by the degree of disarticulation of a skeleton. A study was conducted to determine if these factors truly contribute to the preservation of soft tissue-like structures in the geological record. This study is not intended to verify the presence of proteins but is simply to determine how common are macrostructures that look like soft tissue preservation. Samples were placed into a 0.5 M solution of (ethylenedinitrilo)tetraacetic acid, disodium salt, dihydrate (EDTA) for two months to dissolve mineral components. All specimens studied were collected from the Dinosaur Park Formation (upper Campanian) to minimize stratigraphic variation that may influence preservation. Dissolution of vertebrate remains sampled indicate an unexpectedly high rate of structural preservation. Fifteen dinosaur, two crocodilian, one fish, and one turtle were sampled for a total of nineteen specimens. Specimens were chosen based on sediment type and degree of articulation. Approximately half of the samples were recovered from sandstones, and the other half originated in mudstones. Additionally, approximately half of the samples were collected from articulated or closely associated skeletons, and the other half were taken from isolated bones or specimens from micro vertebrate sites. Of the nineteen specimens tested, eighteen specimens produced "vessel" structures, eighteen had extracellular organic-like matter, and seven revealed "osteocyte" structures. Although "vessel" and extracellular organic-like structures are not associated to a specific matrix type or degree of association, "osteocyte" structures appear to be associated more often with articulated/associated specimens, especially if they are preserved in sandstones.