Hamites - Morphology and Ecology

Morphology and Ecology

Hamites species are characterised by a shell that began with an open, sometimes helical, regular spiral that either opened into a single large hook, or else formed three parallel shafts that gave the mature shell the approximate appearance of a paper clip . No Hamites had spines or other such ornamentation on the shell, but several species appear to have developed apertural modifications when mature; that is, once the ammonite had grown to its final size, the aperture became constricted and was bounded by one or two thickened ribs, known as collars. These have been observed on other ammonites as well, and are assumed to be signs of sexual dimorphism.

The open shell of these ammonites would have made them poor swimmers because of drag, but beyond that fact, very little is certain about their mode of life. It is widely assumed that they were planktonic, perhaps catching small prey in the manner of jellyfish, but repaired shell damage apparently caused by crabs may indicate that they spent at least some time close to the sea floor.