 The distinction between chromosomal sex-determination systems and TSD is often blurred because the sex of some species – such as the three-lined skink "Bassiana duperreyi" and the central bearded dragon "Pogona vitticeps" – is determined by sex chromosomes, but this is over-ridden by temperatures that are tolerable but extreme.Also, experiments conducted at the pivotal temperature, where temperature is equivocal in its influence, have demonstrated an underlying genetic predisposition to be one sex or the other.Temperature-dependent sex determination was first described in "Agama agama" in the year 1966 by .