Sharks first inhabited the waters during this period of the Paleozoic era named for an English county
The first period in the new Mesozoic Era, the Triassic, is an 
interesting time... [DOC] [TLE] Jurassic Period | geochronology | Britannica.com [PAR] Second of three periods of the Mesozoic Era, extending from 201.3 million to ... 
organisms important in the modern world made their first appearance during the 
Jurassic.