I must say everybody is entitled to their own opinion, but i strongly disagree with this German guy Eble. He is by the way a physicist and not a paleontologist, who also claims that archaeopteryx was a underwater swimmer. He states that all ammonoids (heteromorph or not) were benthonic (and by this he mains really benthonic on the bottom and not demersal like some fish). He came to this by making false assumptions on ammonoid growth and his own calculations of negative buoyancy of ammonoids, which were proven wrong by all other studies, which all gave values within the margin of error of neutral buoyancy. If would by the way be very hard to live on the seafloor with a negatively buoyant shell (must of been drag carrying that around). It think it is ok to assume that the hydrostatic apparatus was working, because they all (even the weirdest heteromorphs like Nipponites) posses (and did not lose) their siphuncle. So per definition they would be somewhere in the water column from swimmers to planktonic floaters or vertical migrants. Some of them could have feeded demersally on the bottom (some orthoconic forms without adapical ballast) or potentially gyroconic forms, while other must have unmistakenly fed in the water column with a stabile upward pointed aperture (assuming soft parts filled the entire body chambers => see some of the discussions from Neal Monks)...