About 8 cm long, Microbrachius lived in ancient lake habitats in Scotland, as well as parts of Estonia and China. According to the study, the male members of this ancient species developed bony L-shaped genital limbs called claspers to transfer sperm to females. The females, it was found, developed small paired bones to lock the male organs in place for mating. The male’s organ was nearly as long as his body and rigidly fixed, and it used its small jointed arm-like appendages to achieve the appropriate mating position. The fish are believed to have mated sideways.
The discovery means that sex with internal fertilisation evolved much earlier in the history of vertebrates than previously thought. Since the oldest bony fishes, which follow placoderms in the evolutionary chart, show no evidence of internal fertilisation, the researcher concludes that at some point the internal fertilisation method got lost, before some of their descendants ‘re-invented’ such organs for a similar function. For instance, modern sharks and rays have claspers along the inner part of their pelvic fins that they use to deposit sperm in females.
In a press release put out by Flinders University, Long says, “Placoderms were once thought to be a dead-end group with no live relatives but recent studies show that our own evolution is deeply rooted in placoderms, and that many of the features we have, such as jaws, teeth and paired limbs, first originated with this group of fishes… Now, we reveal they gave us the intimate act of sexual intercourse as well.”