Erbenoceras was one of the first ammonites.
The ammonites that became very common in the Jurassic and Cretaceous periods often had shells tightly coiled in a flat spiral shape. But they originally evolved from straight cephalopods, and in the Devonian a range of early ammonites had shells that were only partly coiled. One of them was Erbenoceras.
This shell shape made Erbenoceras a slower swimmer than the ammonites with fully coiled shells and it was therefore, perhaps, a plankton feeder rather than an active predator.