Plant life on land follows a very different evolutionary pattern - in terms of primary ecosystems - to both land animals and marine life. Whilst the division of the main evolutionary stages of multicelluar life into Palaeozoic, Mesozoic, and Cenozoic is described in many popular science books and educational websites, few people are aware that these terms apply to animal life only. Plant life followed a different route, and the paleobotanical time-eras of Palaeophytic, Mesophytic, and Cenophytic are only approximately equivalent. Palaeophytic refers to the primaril;y spore-bearing (and a few primitive seed-bearing) Paleozoic vascular flora, which appeared in the Middle Ordovician period and die out quite a few millions of years before the end of the Paleozoic (latest early Permian and earlier). In the middle Permian the gymnosperm-dominated Mesophytic flora emerges (although Mesophytic type plants go back to the Carboniferous, just as some Paleophytic plants survive even to this day), and this flourishes right up until the middle and later Cretaceous. At this time, when the dinosaurs and other mesozoic animals are in full swing, the current, angiosperm-dominated Cenophytic flora emerges (in fact Angiosperms appear in the later Early Cretaceous, but do not become predominant until the later Cretaceous). The Cenophytic flora continues quite happily through the great K-T extinction that eliminated the dinosaurs and many other forms of animal life (including some marsupial mammal and early bird types), although some modern biome-types like grasslands only appeared very recently (during the Miocene epoch).
Nothing grabs the imagination like big animals. The dinosaurs in particular are the sexy superstars of the history of life on Earth, by virtue of their great size (although none matched the blue whale), unusual form (although few were as strange looking as a giraffe), and perhaps most of all because they are long vanished, leaving only fossil bones, petrified footprints and other such traces.
Personally I find other types of megafauna (and even not so mega- fauna) just as interesting as dinosaurs. And if one is to consider the magnificent spectacle of the succession of life on Earth, one needs to take these otehr creatures into account as well.
Being at the top of the food chain, big animals are unusually vulnerable to environmental stress. Bacteria have hardly changed in three billion years, but the biggest amphibians, reptiles, birds and mammals that terrified, stomp on, and/or eat their smaller contemporaries come and go. And it is quite a fascinating pastime to watch and record their comings and goings.
The following diagram by Dr Bob Bakker from classic work The Dnosaur Heresies (Longman Scientific & Technical, 1986) illustrates the major biotas or Megadynasties (ecological communities) of terrestrial megafauna.
Four Megadynasties are listed, reflecting the changing sucession of Theropsids (Synapsids - Protomammals and Mammals - left on diagram) and Sauropsids (reptiles, chiefly archosaurs, right half of diagram). Each megadynasties can be divided into a succession of empires. Each empire is in a sense an evolutionary pulse, a new adaptive radiation. Allowing for the contemporary dicynodont-cynodonts and aetosaurs-rhynchosaurs that gives twelve altogether, although either more or less could be postulated. Also, not all these dynasties were widespread. The duckbill-horned dinosaur (or hadrosaur-ceratopsian to give a more technical sounding term) dynasty, in which the great T. rex and it's cousins were the top preditors, was limited to a single large island that encompassed what is now East Asia (Mongolia, China, Japan, etc) and western North America. The fact that dinosaurs from the hadrosaur-ceratopsian biota feature in popular movies and fantasy gives the mistaken impression that these animals had a worldwide distribution (the Hadrosaurs, to be sure, did make it to Europe and South America, but the ceratopsids and tyrannosaurs did not)
The following are a list of megafauna dynasties defined according to the predominant herbivores (time period in brackets)