THE POSITION OF GRAPTOLITES WITHIN LOWER PALEOZOIC PLANKTIC ECOSYSTEMS

An integrated approach has been used to assess the palaeoecology of gr aptolites, both as a discrete group and as a part of the biota present within Ordovician and Silurian planktic realms. Study of the function al morphology of graptolites and comparisons with Recent ecological an alogues demonstrates that graptolites most probably filled a variety o f niches as primary consumers, with modes of life related to the colon y morphotype. Graptolite coloniality was extremely ordered, lacking an y close morphological analogues in Recent faunas. To obtain maximum fu nctional efficiency, graptolites would have needed varying degrees of coordinated automobility. A change in lifestyle related to ontogenetic changes was prevalent within many graptolite groups. Differing lifest yle was reflected by differing reproductive strategies, with synrhabdo somes most likely being a method for rapid asexual reproduction. Direc t evidence in the form of graptolithophage 'coprolitic' bodies, as wel l as indirect evidence in the form of probable defensive adaptations, indicate that graptolites comprised a food item for a variety of preda tors. Graptolites were also hosts to a variety of parasitic organisms and provided an important nutrient source for scavenging organisms.