Biomolecules in fossils of cenozoic mammals: claims of non-mineralized soft tissues in fossils recovered from different taphonomic contexts

The discoveries of non-mineralized soft tissues in fossils have increased in recent years, especially those in depositional environments of cave, ice, amber and tar pit, as these are supposedly more taphonomically conducive to the preservation of these structures. Therefore, the aim of this study was to review scientific articles from the last six decades to verify the frequency of non-mineralized soft tissue findings in fossils of Cenozoic mammals recovered from different taphonomic contexts. For the appropriate purposes, a systematic review of English-language articles was carried out by peers and available on the platforms PubMed, Scielo and CAPES, which present the descriptors “fossil mammals”, “soft tissues”, “exceptional preservation”, “ fossils of cenozoic "," ancient protein "and" ancient DNA ". In the search, claims were delimited that had no cases where the organic material was completely replaced by minerals (mineralized soft tissues) and that the original molecules had not been recovered from depositional environments less favorable to taphonomic preservation (fluvial, wind and lake sedimentary deposits) ; reports of findings in fossils of non-cenozoic layers and of articles that, although they claimed the presence of the mammal's original organic material, were not included in their information. The results identified 15 articles that described the presence of non-mineralized soft tissues for extinct representatives of seven different orders (Artiodactyla, Carnivora, Metatheria, Perissodactyla, Pilosa, Primates and Proboscidea), distributed in 9 taxonomic families. Of these, the most identified biomolecules were collagen proteins (38.9%), fragments of mtDNA and nuDNA (27.8%), keratins (11.1%) and albumin (11.1%). The most used analytical techniques for biochemical detection were those of biological bases (35%), followed by chemical (27%), optical (23%) and detections that did not use such analytical methods (15%). The most frequent depositional environments were periglacial (27%), karst (21%) and infiltration (16%), although many articles do not present the referred information (26%). The distribution of non-mineralized soft tissue findings in fossil mammals recovered from different taphonomic contexts is global (with the only continent without reports being Antarctica), with Russia, specifically Siberia, being the country with the largest number of findings (40%) until now