The Mesozoic literally means 'middle animals', because it is the middle Era in which animals thrived on Earth. It is from 251-65.5 million years (Ma) ago and includes the Triassic (251-199.6 Ma), Jurassic (199.6-145.5 Ma) and Cretaceous (145.5-65.5 Ma) Periods. During the Mesozoic, both the landscape and life on Earth changed drastically. It saw the breakup of Pangaea, the large supercontinent that had existed previously, and the introduction of many new plants and animals. By the end of the Cretaceous, the continents had started to move to the relative positions seen today, and the major land masses were present.
|Sorry about the quality: the captions from top left are Permian, 225 million years ago, Triassic, 200 Ma ago, Jurassic, 150 Ma ago, Cretaceous, 65 Ma again, and Present Day|
Image from http://pubs.usgs.gov/gip/dynamic/historical.html
The Mesozoic is commonly known as "the age of the dinosaurs", or in terms of plants, "the age of the cycads". Dinosaurs first appeared in the Triassic, and survived until the end of the Cretaceous, living for over 150 million years. Pterosaurs, which are often mistakenly called dinosaurs, lived during the same time as the dinosaurs, also going extinct 65.5 Ma ago. Another major group that evolved during the Mesozoic was birds. Birds evolved from small theropod dinosaurs, and are therefore dinosaurs (biologically speaking). This is why you will sometimes see the distinction between avian (birds) and non-avian dinosaurs. The first birds include animals like Archaeopteryx, a beautiful fossil that shows features of both dinosaurs and birds, and may have been able to fly. They appear during the Jurassic Period. Mammals also evolved, with the first ones appearing at the end of the Triassic, 205 Ma. Mammals were relatively minor aspects of the Mesozoic fauna, and only became very diverse and common after the non-avian dinosaurs went extinct at the end of the Cretaceous.
|A fossil of Archaeopteryx, one of the first birds from the Solnhofen limestone in Germany.|
Picture from Wikimedia Commons
Plants changed substantially during the Mesozoic as well. For most of the Mesozoic, only gymnosperms existed. Gymnosperms are the 'naked seed' plants, because of the unenclosed nature of their unfertilised seeds, vs. angiosperms (aka flowering plants) that have their ovaries encased within an ovule. Gymnosperms in the Mesozoic include ferns, cycads, ginkgophytes and other strange plants no longer present today, and were common during the Triassic. Conifers, a very common group of modern gymnosperms, started to appear in the Triassic, with modern groups in the Cretaceous. Angiosperms didn't evolve until the Early Cretaceous, with much diversification during the Late Cretaceous. This means that most herbivorous dinosaurs weren't eating leaves like what we think of today from big deciduous trees, but rather things like ferns (including some giant ferns), ginkgos, cycads, and conifers. Check out our short educational video on 'Plants of the Mesozoic Era' for more information.
|Typical Mesozoic landscape from Germany from Wikimedia Commons|
The end of the Mesozoic is marked by another large mass extinction, in which all non-avian (non bird) dinosaurs, pterosaurs, and many other animals went extinct. Two main debates about the cause of this extinction exist and consist of a large meteor impact that hit on the Yucutan Peninsula in Mexico (the Chicxulub crater), and hugh volcanic eruptions that occurred in Indian (the Deccan Traps). Although most scientists believe it was caused by the meteor impact, there are a number of people that believe the volcanic eruptions were the main cause, or at least somewhat to blame. Take a look at our 'K-T Extinction Event' video to learn more.
http://en.wikipedia.org/wiki/Mesozoic -> Of course use caution when using Wikipedia as a source, as anyone can change it. That being said, this page seems to be quite accurate, and provides lots of information I didn't include!