[Marika (OP)]

David wants to know:

From a biological point of view, what is the exact biological process within certain species of turtle or crocodiles, where temperature determines what sex the young will be? How is this achieved?

What do you think?

[evan_au]

There are hormones that can bias the impact of temperature on sex, so it is thought that temperature may be influencing the production or detection of signals on this hormone pathway.

There are also some species where the sex is determined genetically, but can be overriden by extremes of temperature.
See: https://en.wikipedia.org/wiki/Temperature-dependent_sex_determination#Hormones_in_TSD_systems