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The Petrified Forest
Petrifaction happens when minerals in groundwater replace organic matter molecule by molecule, so the shape survives while the substance is exchanged. The Chinle Formation preserves an entire Late Triassic ecosystem: the conifer Araucarioxylon, early crocodile-like phytosaurs, and the very first dinosaurs in North America, still small and unremarkable among larger reptiles. The beds sit just below the boundary where the great dinosaurs take over, and are therefore important for understanding that dinosaur dominance was not given but followed from an extinction that hit their competitors harder.
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