Sticky orange coating on a 6,000-year-old Yukon dart came from a beaver's anal sac

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A 6,000-year-old feathered dart recently discovered in the Canadian Yukon was smeared with castoreum, a sticky, orange secretion produced in the anal sacs of beavers.

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This is the first time that castoreum has been chemically identified in the archaeological record, and the dart is the earliest evidence of the substance's use on an ancient weapon, scientists recently reported. The researchers aren't sure why the anal secretion was applied to the dart, though it could have been as a way to preserve it, decorate it or even reinforce it

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The dart, which measured about 6.6 feet (2 meters) long, is known as an atlatl, a segmented throwing weapon made of three sections of birchwood bound together with animal sinews and fletched with feathers. Reddish-orange residue coated the dart in two places near the weapon's joints

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At first, scientists thought that the residue on the dart might be red ochre — a natural clay pigment — or adhesive colored by ochre, as ochre-tinted spruce resin was previously identified in other artifacts from this Yukon region. Using surgical tools, the researchers carefully removed small samples of the residue for chemical analysis, and found that the residue came from beavers' back ends.

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Beavers' castor sacs lie between the base of the tail and the pelvis; they are located internally near the cloaca, and beavers secrete paste from these glands for scent marking, the researchers reported. When fresh, "castoreum is a sticky, semi-liquid paste and becomes solid with a waxy to resinous texture as it dries,"

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