The start and end of the period are defined by carefully selected locations; the uncertainty in dating arises from trying to date these horizons.The chronostratigraphic term "Jurassic" is directly linked to the Swiss Jura Mountains.. 
jẹ́ ará Nàìjíríààìtọ́kasí àwọn Ọjọ́ìbí níàwọn ara Nàìjíríà..