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orthocone is known in Antarcticeras, which may be a descendant of the orthoceratoids and has an orthocone-like shell that is thought to have been weakly mineralized and internal, in contrast to the external, fully-mineralized shells of earlier orthocones--an example of convergent evolution with the coleoids. However, other studies have recovered it as an oegopsid squid. Orthocone nautiloids

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