Didymoceras Stevensoni Heteromorph Ammonite Fossil on Matrix, South Dakota.
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An exceptional and highly sculptural heteromorph ammonite fossil, Didymoceras stevensoni, preserved and mounted upon its original sedimentary matrix from the Pierre Shale of Custer County, South Dakota.
Unlike the familiar tightly coiled form associated with most ammonites, Didymoceras developed an extraordinary open, helically coiled shell, producing the dramatic looping configuration seen in this specimen. The exposed shell rises prominently from the matrix, displaying pronounced ribbing, projecting tubercles, and the remarkable irregular geometry characteristic of this uncommon Late Cretaceous cephalopod.
The warm brown fossilized shell contrasts beautifully against the pale buff-colored shale matrix, while associated fossil material embedded within the stone further emphasizes its geological context. Presented almost as a natural sculpture, the specimen has a strong three-dimensional quality and can be appreciated equally as an important natural-history object and as a sophisticated decorative piece.
Didymoceras stevensoni is a recognized nostoceratid heteromorph ammonite occurring within the Pierre Shale. Current stratigraphic references place its zone in the Upper Campanian at approximately 75.2–75.1 million years ago.
Dimensions: Height: 7 in. x Width: 8 in. x Depth: 4.5 in.
Details
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Species: Didymoceras stevensoni (Whitfield, 1877)
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Type: Heteromorph / uncoiled ammonite
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Formation: Pierre Shale
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Geologic Period: Late Cretaceous
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Stage: Upper Campanian
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Age: Approximately 75 million years
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Locality: Custer County, South Dakota
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Country: United States
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Material: Fossil ammonite on natural matrix