The origin or evolution of new types of biological organization as a result of general adaptation from its predecessor, resulting in the formation of new classes, groups of phyla is known as a mega evolution. Mega evolutionary changes are rare and have occurred only a few times in the evolutionary history of living beings. But the most interesting thing is that all these biological organizations persist without extinction (with few exceptions). All the phyla and most of the classes of microorganisms, plants, and animals represent their separate organization and are produced as a result of mega evolution.
Features of Mega Evolution:
The fossil evidences in favour of mega evolution are relatively rare. The special features of mega evolution are-
Mega evolution includes experimentation and exploitation of new zone by the members of the ancestral stock in several divergent lines. This experimentation involves appearance of new characteristics, which may prove suitable for a new zone.
Mega evolution operates individuals, which have developed some general adaptations for the new zone.
The pre-adapted group of individuals then crosses the ecological barriers and makes a breakthrough into the new zones.
The breakthrough and shifts are always rapid, otherwise they fail on account of extreme negative selection.
The new zone is always ecologically accessible and is devoid of competition.
The initial shift is always followed by adaptive radiation, which is actually macro evolution.
Examples of Mega Evolution:
The origin of amphibians from fishes, origin of reptiles from amphibians and the origin of birds and mammals from reptiles afford the best examples of mega evolution.