Mesozoic

The Mesozoic Era (252 million years ago to to 66 million years ago) is a geologic span of time on Earth which includes the Triassic, Jurassic and Cretaceous Periods, an era populated by dinosaurs.

Conditions in this era included seismic activity, volcanoes, and violent storms. Lifeforms included tree ferns and pterosaurs. 

History
252 million years ago, 90% of Earth species died within a span of one million years during the Permian-Triassic Extinction Event. 

65 million years ago, an asteroid impact near the Yucatan Peninsula in Mexico created an extinction event that killed off most of the dinosaurs.

In an alternate timeline when the impact was prevented, descendants of Mesozoic wildlife were discovered on Earth by the USS Enterprise (NCC-1701), including ammonites, shellfish, plesiosaurs, man-o-wars, and sharks. 

Other planets
In 2269, the plant and animal lifeforms on the planet Anomaly were described as Mesozoic in nature. 

In 2270, Lieutenant Commander Piper saw a holographic projection of her homeworld of Proxima Beta. She saw features representing an early part of the Mesozoic Era, replete with blooming cycads and conifers. She expected to see club moss, algae, lichen, moss, and dragonflies as well. 

In 2371, during a survey of the Trige sector by USS Bonestell, Captain Kathryn Janeway's interest was piqued by a planet that resembled Earth during the Mesozoic Era. When she and Tuvok were trapped by a pterosaur in a cavern, she told him that she'd been offered command of USS Voyager and asked him to join her there. 

In 2376, when a waitress at a tavern thought he was from a race of "rock people", Zak Kebron asked to be served magma and said he had previously visited the bar in the Mesozoic Era. 

In 2269, the planet Vesbius supported mosses, rushes and ferns like those of the Mesozoic Era. 

Mesozoic-type planets

 * Anomaly
 * Coltac
 * Earth (past)
 * Neesan
 * Proxima Beta
 * Trige sector planet
 * Vesbius