A graptolite (extinct hemichordate) from the lower Ordovician Al Rose Formation, Inyo County, California, called scientifically Didymograptus sp. Golden to reddish-brown coloration of specimen derives from replacement of original rhabdosome colony by the mineral limonite, a variety of hydrated iron oxide. The actual colonial graptolite animal lived inside those "notches" on the inside of the wishbone-shaped rhabdosome.

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