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Geopic of the week: Asterosoma

Above is a commonly misunderstood geologic feature called an Asterosoma.  Almost everyone, upon first seeing an Asterosoma, thinks it’s either a fossilized plant, flower, or some kind of fossilized animal – usually an octopus.

Asterosomas are actually trace fossils left behind by ancient marine animals (most likely worms or shrimp) that burrowed through mud in a delta or tidal-flat.  This one was found in the Carboniferous section of north Arkansas and is roughly 300 million years old.  These trace fossils are called Asterosoma because of their star-like shape.

In cross-sectional view, multiple Asterosomas sometimes overlie one another connected by a central vertical tube – like a garland of Asterosomas.  This suggests that, as new sediment was periodically washed into the environment, the animal may have burrowed its way back to the top of the mud and wallowed out another home for itself.  The animal itself was too soft-bodied to be preserved in the rock record.

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