[sureLoss]

Originally Posted by Traditional_Ale

Except in the pilot episode of Enterprise they return a Klingon to Kronos and he has the bumpy forehead.

Yup, at the start of Enterprise the Klingons had a bumpy forehead. However later on Enterprise had a couple of episodes dedicated to telling the story of how the Klingons ended up with a more human type of forehead they had in TOS.

Spoiler-ed in case anyone ends up watching Enterprise.

Spoiler!

The Klingons began experimenting in genetically enhancing themselves after encountering and having their asses kicked by genetically augmented humans in a previous Enterprise episode.

However, the Klingons accidentally made a previously harmless virus deadly to them in the process. Eventually a vaccine is discovered but a side effect would be the Klingons would lose their forehead ridges for a couple of generations.

But who knows... the Klingons that were in Star Trek Into Darkness looked completely different than any of the Klingons that were previously shown in any Star Trek franchise.