Reconstruction of squidlike belemnoid cephalopods from the Cretaceous System, southern Tennessee
Member of an extinct group of cephalopod
s, possessing a large internal shell, that first appeared circa
345 million years ago, in the Early Carboniferous Period
, and became extinct during the Eocene Epoch
, which ended circa
36.6 million years ago. The internal shell of most species is straight, but that of some species is loosely coiled. The shell served for support and muscle attachment and enabled the animal to compensate for depth and its own body weight. Seealso ammonoid
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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.