Gigantoproductus giganteus ("Gigantic giant Productus"[2]) is an extinct species of brachiopods in the family Monticuliferidae,[3] known only from its fossil remains.

The valves had a small number of broad ribs that radiated from a thick umbo and there were large wing-shaped ears of calcareous material on either side.

[5] These are visible in an internal mould of the brachiopod, a cast fossil which has been formed when a hole in sediment left by the soft tissues of the dead organism was later infiltrated by mineral matter.

[1] The morphology of the shell makes it likely that it lived on the seabed, partially buried in sand or mud, in shallow water in locations with strong waves and currents.

[2] Like other brachiopods, Gigantoproductus giganteus was a filter feeder, using its lophophore, a specialist feeding organ, to extract planktonic particles from the water.