Orthocerida

-Cephalopod group which seems to resist all attempts for a practical and useful classification.

-As with other celphalopods, (Nautiloidea, Ammonoidea), has univalve shell composed mostly of aragonite.

-Shell is filled with gas, and has one or more chambers within it through which it can govern buoyancy.

-Soft bodied "foot" is modified to ring of tentacles around mouth.

-Was already in dramatic decline going into Permian, and continued to decline throughout Permian.

-Only two genera and one genus survive into Triassic which became extinct quickly.

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