Well preserved fossils
Macri and his colleagues first learned about McGrath’s site in 2017. Once the importance of these fossils came to them, they went there for three to four days in a row. They opened their hands to the flint-like rocks as they tried to peek into a primeval forest.
As the research progresses, they discover how special the method of preservation is. All the fossils were trapped in extremely thin layers of an iron and oxygen-containing mineral called goethite. Fossils have been found in such rocks before, but the quality of the finds from McGraths Flat is extraordinary.
“Little or no attention has been paid to this form of preservation,” said one of the study’s leaders, Michael Freese, who is a virologist at Australia’s University of Canberra who also studies microfossils. “If you asked people if they really believed that ironstone could contain beautiful fossils, they would probably say, ‘Don’t be silly!'”
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He explains that the finds from McGraths Flat can be analyzed well with a scanning electron microscope (Scanning Electron Microscope, SEM) due to their unusual method of petrification. This is one of the most powerful microscopes out there. Researchers often have to coat the objects they want with SEM with a thin layer of gold or platinum, which may limit future studies of these objects. Fossils from McGraths Flat already contain a lot of iron and are so conductive that they can be placed directly under an electron microscope, without additional preparation.
“The fossil exits the SEM the same way it went in,” Freese said.
The smallest fossils have already yielded some great discoveries. In the only fossil feathers known from the site, researchers can see accumulations of the pigment melanin. Its shape indicates that the plumage was dark or iridescent in color. The scientists also saw melanin in the eye of a fish fossil, and even found a scale separate from the wing of a butterfly or moth that lived more than 11 million years ago.
