Exceptional Preservation of Non-Mineralized Biomaterials in Fossils of the Avialae Clade

Thousands of primitive and diverse fossils birds from Mesozoic and Cenozoic have been discovered around the world. Among these, hundreds of studies have found exceptional preservation of mineralized biomaterials, allowing to expand the knowledge about the ecology and Evolution of birds. However, the Avialae clade presents scarce data regarding non-mineralized biomaterials, and those that have already been identified are dispersed in the scientific publications, associating the idea of the findings with isolated phenomena. This paper presents a review of the literature published in the last two decades, in order to better understand the frequency of nonmineralized biomaterials findings in fossils of the Avialae clade. 12 articles describing original biocomponents for representatives of Anchiornithinae, Confuciusornithidae, Enantiornithes and Euornithes were found. Among these, the molecules of proteins (50%) and melanins (41.7%) showed higher frequency of findings. In general, although the data for the groups were not shown to be taxonomically comprehensive, there was a wide geographic distribution across the globe regarding original biochemicals in mesozoic and cenozoic rocks. However, it is believed that the frequency is underreported and, from the emergence of new technologies, the forecast is that more organic biomaterials will be identified in the fossils.