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.. 
Yàtọ̀ sí ohun orin tí kò láfiwé, ó tún ń sin ẹyẹ olóhùn dídùn tíirìn nínú ilé tó ń gbé.Ìtọ́kasí àwọn Ọjọ́ìbí ni àwọn olórin ará Nàìjíríà.. 