Several mass extinctions are recorded in the fossil record.
Paleontologists have been able to recognize patterns within and
between extinction events. Currently, there are five major
extinction patterns recognized. Steven M. Stanley, has outlined
them in his book entitled, Extinction. - Extinction strikes in
both the land and the sea. - On the land, while animals suffer
repeatedly, plants tend to be highly resistant to mass
extinctions. - Preferential disappearance of tropical forms of
life during mass extinctions. - Tendency of certain groups of
animals to experience them repeatedly (for example, trilobites
and ammonoids). - Alleged equal spacing, or periodicity in
geological time (occurring about every 26 million years). These
similarities between distinct extinction occurrences aid
paleontologists in determining the agents the agents that
perpetuated the disappearances of species in each extinction
event. Such agents are currently divided into two types: -
Catastrophic Agents- such as meteorite impacts and