Evolutionary biology key terms

An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity.
A significantly large and diverse radiation within a relatively short geologic time scale is often referred to as an explosion.
Radiations may affect one clade or many, and be rapid or gradual; where they are rapid, and driven by a single lineage's adaptation to their environment, they are termed adaptive radiations.

In evolutionary biology, a key innovation, also known as an adaptive breakthrough or key adaptation, is a novel phenotypic trait that allows subsequent radiation and success of a taxonomic group.
Typically they bring new abilities that allows the taxa to rapidly diversify and invade niches that were not previously available.
The phenomenon helps to explain how some taxa are much more diverse and have many more species than their sister taxa.
The term was first used in 1949 by Alden H.
Miller who defined it as key adjustments in the morphological and physiological mechanism which are essential to the origin of new major groups, although a broader, contemporary definition holds that a key innovation is an evolutionary change in individual traits that is causally linked to an increased diversification rate in the resulting clade.