What type of organisms lived in the mesozoic time period?

There were far too many organisms in the Mesozoic that have been discovered to list, and what has been discovered is only a fraction of what actually existed. Here is the list for you:

Animals

In the Air:

Insects

Pterosaurs

The first birds (some of which had teeth)

On Land:

Dinosaurs

Small mammals (multi-tuberculates, placentals, marsupials, and monotremes)

Lizards

Amphibians (frogs, salamanders, and the last temnospondyls [huge, toothed amphibians])

Insects

In the Ocean:

Fish

Coral

Sharks

PlesiOSaurs (marine reptiles, some of which had long necks)

Icthyosaurs (marine reptiles that looked like fish)

Mosasaurs (huge marine lizards)

Plants

Ferns and Tree Ferns

Conifers

Cycads

Bennettitales

The first angiOSperms (flowering plants) appeared during the end part of the Cretaceous