North Dakota: Teredo petrified wood (state fossil)
North Dakota: Teredo petrified wood (state fossil)
North Dakota's state fossil is a peculiar type of petrified wood, called Teredo petrified wood. This wood bears the boreholes of shipworms, genus Teredo, hence its name. Shipworms are actually a type of mollusc (not worms at all) that were the bane of mariners past and still wreak havoc today on wooden boats and dock posts.
During the Paleocene Epoch, about 60 million years ago, North Dakota was partially covered by the last seaway to invade North America, the Cannonball Sea. The swamps and lowlands bordering this sea -- not too different from Florida today -- were home to 50 foot long crocodiles and giant predatory birds. The marine fauna includes bony fish and sharks, crabs, lobsters, snails, and clams. Trees that washed into the sea were frequently attacked by shipworms before they were fossilized, leaving them riddled with holes. This wood belongs to a variety of species, including bald cypress, ginkgo, redwood, and magnolia trees.
Teredo petrified wood is one of the most common North Dakota fossils and is known almost exclusively from the Cannonball Formation, and the best collecting sites are in the south-central portion of the state. Collectors frequently polish the wood and make it into bookends and paperweights.
Because of the uniqueness of this petrified wood and its popularity with collectors, the state legislature named it the state fossil in 1967, making North Dakota one of the first states to designate an official fossil.
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