 Trilobites appear to have been primarily marine organisms (though some trackways suggest at least temporary excursions unto land), since the fossilized remains of trilobites are always found in rocks containing fossils of other salt-water animals such as brachiopods, crinoids, and corals.Within the marine paleoenvironment, trilobites were found in a broad range from extremely shallow water to very deep water.Trilobites, like brachiopods, crinoids, and corals, are found on all modern continents, and occupied every ancient ocean from which Paleozoic fossils have been collected.