20 October 2014–16 November 2014
North Foyer, Ground floor
How the earliest vertebrates reproduced
This display shows the earliest record of male and female sexual structures appearing in the evolution of vertebrates.
These tiny fish (Microbrachius dicki) lived in ancient Scottish lakes and are 385 million years old – nearly twice the age of the first dinosaurs.
They belong to a very primitive fish group called antiarch placoderms, yet exhibit very advanced adaptations for reproduction – similar to those found in guppies today.
They possess ‘sexual dimorphism’, meaning males and females are very distinct: the male bore a large L-shaped genital structure (called a ‘clasper’) and the female had an ornamented pair of plates in her pelvic region, to receive the tip of the male clasper and lock it in place. This indicates they reproduced by copulation, with the male transferring sperm along grooves seen in his clasper.
They probably gave birth to live young. Small antiarch placoderms are already one-quarter as long as adults, suggesting they spent substantial time growing inside the mother. Other types of placoderms have even been found preserved with young inside.
Read more about the research in Unlocked: Stories from our Scientists.
This Science Unlocked display is a showcase of a scientific research paper published in Nature. The research was led by Prof John Long (Flinders University & Honorary Research Associate, South Australian Museum) with Adelaide researchers Dr Brian Choo (Flinders University) and Dr Mike Lee (South Australian Museum & University of Adelaide).