<Tr> <Td> Mean surface temperature over period duration </Td> <Td> c. 16.5 ° C (3 ° C above modern level) </Td> </Tr> <Tr> <Td_colspan="2"> Key events in the Jurassic view discuss edit - 205---- - 200---- - 195---- - 190---- - 185---- - 180---- - 175---- - 170---- - 165---- - 160---- - 155---- - 150---- - 145---- s o z o i Triassic J u r s s i Cretaceous r l y i d d l Hettangian Sinemurian Pliensbachian Toarcian Aalenian Bajocian Bathonian Callovian Oxfordian Kimmeridgian Tithonian An approximate timescale of key Jurassic events . Vertical axis: millions of years ago . </Td> </Tr> <P> The Jurassic (/ dʒ ʊəˈr æsɪk /; from Jura Mountains) was a geologic period and system that spanned 56 million years from the end of the Triassic Period 201.3 million years ago (Mya) to the beginning of the Cretaceous Period 145 Mya . The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles . The start of the period was marked by the major Triassic--Jurassic extinction event . Two other extinction events occurred during the period: the Pliensbachian / Toarcian event in the Early Jurassic, and the Tithonian event at the end; however, neither event ranks among the "Big Five" mass extinctions . </P> <P> The Jurassic period is divided into three epochs: Early, Middle, and Late . Similarly, in stratigraphy, the Jurassic is divided into the Lower Jurassic, Middle Jurassic, and Upper Jurassic series of rock formations . </P>

When did the jurassic period start and end
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