Microrelief on the exoskeleton of some early Osteostracans (Agnatha): preliminary analysis of its significance

The surface of the osteostracan exoskeleton has been studied using the SEM on isolated microremains, and small fragments taken from complete cephalothoracic shields. The material comesfromthe Silurian and Lower Devonian deposits of Severnaya ZemlyaArchipelago, Russia, and Saaremaa Island, Estonia. Imprints of epidermal cells on the exoskeleton surface are described forthe first time in osteostracans. It is concluded that the sculpture on the osteostracan exoskeleton, both macrosculpture and microsculpture, reflects processes of the probable mode of ossification ofthe osteostracan hard cover. On the other hand, varioustypes of microsculpture (microtubercles, fine ribs orstripes, microapertures) in general are related to the functional peculiaritiesresponsible for animals’ adaptation to the ambient environment, and were necessary for the implementation of metabolic processes in different covering tissues of early vertebrates.