11–16 Million-Year-Old Miocene Rainforest Fossils Perfectly Preserved in “Rust” at McGraths Flat, Australia

Beneath dry farmland in central New South Wales lies one of the world’s most extraordinary fossil sites: McGraths Flat. Dated to the Middle Miocene (11–16 million years ago), the deposit has yielded hundreds of three-dimensionally preserved organisms—plants, insects, spiders, fish, and more—encased not in shale or limestone, but in goethite, a fine-grained iron oxide-hydroxide mineral commonly known as “rust.”

Discovered in 2020 and detailed in Science Advances (2022) with major follow-up studies in 2025–2026, the site formed when iron-rich groundwater, leached from weathered basalt under warm, humid rainforest conditions, flowed into an oxbow lake and precipitated as ultra-fine ferricrete. Particles just 0.005 mm across infiltrated and replaced every cell, preserving soft tissues, colors, and even microscopic structures in stunning detail.

Among the treasures: trapdoor spiders with intact fangs, fish with preserved gills and scales, winged insects, and a diverse flora that reveals a lush subtropical rainforest teeming with life—before Australia’s climate dried and the continent’s rainforests contracted dramatically.

“This mode of preservation was thought impossible in iron-rich settings,” noted lead researcher Matthew McCurry. “Yet the nanoscale iron particles acted like a natural cement, replicating organisms cell by cell.”

McGraths Flat is rewriting the rules of Konservat-Lagerstätten. It proves that iron oxides—long dismissed as poor preservers—can rival the finest shale sites when conditions align. The fossils offer an unparalleled window into Australia’s Miocene ecosystems, showing how the continent’s biodiversity responded to gradual aridification long before the Pleistocene.

After millions of years hidden beneath farmland, the “rust” of McGraths Flat has delivered one of the most vivid snapsH๏τs of a lost Australian rainforest ever found.