Flatfish follow up: Following our item on the fossil fish with asymmetrical eyes one of our readers wrote: “Interesting commentary on the Heteronectes ‘evolution’. However, since modern flatfish eyes DO migrate around the head, could this not be just another case of a fossil found in a mid-range developmental state? After all, flounders don’t just wake up one day and boom! Their eyes have shifted to one side, do they?”

Editorial Comment: This is a good point. However, the researcher who first described the fossil in 2008 did answer this question. He gave the following three reasons for believing this was an adult form:
1. There is more than one specimen with this same configuration.
2. The head bones are fully ossified, i.e. have finished growing.
3. The specimens are present day adult size. In living flatfish eye migration starts while they are still quite small.

He also pointed out there are living fish that sit propped up on the sea floor, rather than lying flat, and asymmetrical eyes would be useful for a fish with this habit. Therefore, there is good reason for thinking this fossil is a fully functional adult form.

Evidence News 1 August 2012