and structures used for mating. Differences from other groups Microbrachichiidae is identified as earliest branching placoderm lineage with claspers. Other placoderm groups such as ptyctodonts and arthrodires display evidence of similar innovations. The clasper structure in Microbrachius is clearly different from the pelvic girdle and pelvic fin. In other more derived antiarchs such as asteolepidoids and bothriolepioids, there is a complete lack of pelvic girdle and fins. In ptyctodont and arthrodire placoderms, the clasper is immediately posterior to the pelvic fin. Arthrodire claspers do not articulate directly with the pelvic girdle or fin. In ptyctodonts, the endoskeleton of the clasper was unossified (unknown affinity to other structures) but away from pelvis. Placoderms differ from chondrichtyans by having their claspers independent from the pelvis and pelvic fin. Mating behavior One such specimen shows two individuals preserved next to each other in what has been inferred to be side by side mating. As the male and female engaged in coitis, the animals have interlocked claspers to genital plate in a side by side position. Additionally the specimens show the use of interlocked pectoral appendages, possibly to additional help copulation. Implications New specimens of M. dicki have started the conversation of which is the primitive state for reproduction in vertebrates, internal or external fertilization? The traditional model is that external fertilization is the primitive state with internal fertilization evolving at different times in different clades. The discovery of mating specimens M. dicki gives the oldest proof of internal fertilization in jawed vertebrates. This lends credence to the possibility that internal fertilization evolved first and that actinopterygian fish and most lissamphibians (living amphibians) modified or lost these claspers and plates into forms for external fertilization. References Placoderms of Asia Placoderms of Europe Devonian placoderms Antiarchi Fossils of China Biota of Orkney Placoderm genera