As I understood it, the dashed line is just the 35°C wet bulb temperature line.
I think it’s the “old assumed border of survivability” and don’t know if it is based solely on mathematics or on other experiments as well.
I also don’t know on how many individuals the new line is based and what age group the older people one is.
Aren’t these changes, because there are just have bones to look at, so skin properties etc are a guessing game?
But how did that jaw bone double in length in 2001? Was the skull a missing part until then?