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Through the analysis of fossils dating back 200 million years evidence of internal fertilization in placoderms was discovered. They were the first back-boned creatures to evolve male genital organs called claspers leading to more complex form of sexual reproduction.

Fossilized remains of a small female placoderm appeared to have an embryo and umbilical cord attached during found during a discovery in the Gogo Formation, near Western Australia, The female placoderm was found to have died giving birth with the offspring and umbilical cord intact, also containing more internally fertilized eggs and a internal uterus.

For male placoderms bony pelvic girdles and claspers were developed as completely different structures. Extra pair of appendages, not attached to the pelvic fin allowing movement, which develop into parts used for reproductive purposes only. It was found that jaws appeared in placoderms around the same time as they developed claspers indicating possible connection in early reproductive behaviorIn addition to aiding in the capture of prey, feeding and ventilation, jaws may also have been utilised for holding on to a partner whilst mating.

Placoderm claspers are not homologous with those found in cartilaginous fish like the shark, in sharks claspers are specialized parts attached to pelvic fins Similarities revealed to be an example of convergent evolution since the structures are analogous and have similar function yet the species are not closely related.