Almost every geologic period ends with some sort of extinction event. There is some evidence for this happening at the end of the Jurassic, although not by any means a major extinction event (unless it was your species that became extinct!).
No the Cambrian Period came before the Jurassic Period.Periods in the Paleozoic Era (542 - 251 Ma) and the Mesozoic Era (251 - 65.5 Ma) Cambrian (542 - 488.3 Ma) Ordivician (488.3 - 443.7 Ma)...