Shastasaurus pacificus was a large ichthyosaur, known for its streamlined body and elongated, dolphin-like shape. It inhabited the oceans during the Late Triassic period. Unlike many other marine reptiles, it lacked teeth and likely fed by suction, consuming soft prey such as squid.

Shastasaurus pacificus is primarily known from fossil records found in North America, specifically in the region that is now California. Fossils have been discovered in the Shasta County area, which is how the genus received its name.

Shastasaurus pacificus lived during the Late Triassic period, approximately 210 million years ago. During this time, the area was part of a tropical to subtropical marine environment with warm, shallow seas. These conditions were conducive to the marine life that thrived during the Triassic.

Shastasaurus pacificus was an ichthyosaur, an extinct group of marine reptiles. It occupied a niche as a large marine predator, feeding primarily on cephalopods and other marine life. Its streamlined body and adaptations for swimming suggest it was well-suited to an open-ocean lifestyle, making it a dominant predator in its ecosystem.