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Magnetofossils are the fossil remains of iron-biomineralizing organisms. They are classified into two general categories: conventional and giant magnetofossils. Conventional magnetofossils comprise the~ 20-100 nm-sized equant, prismatic, and bullet-shaped particles made by magnetotactic bacteria (MTB). In contrast, giant magnetofossils are~ 1 µm (or larger) needle, bullet, spindle, and spearhead-shaped particles made by as yet unidentified organisms. The stable single-domain magnetic state of most magnetofossils, and thus their correspondingly distinct magnetic coercivity components, makes them distinguishable in bulk sediments using non-destructive component-specific magnetic measurements. Some of the organisms responsible for these components flourish in specific environmental conditions and thus may be proxies for environmental change throughout the geologic record. This proxy development …