Q-2.The history of mammals dates back at least to Triassic time.Development was retarded,however,until the sudden acceleration of evolutional change that occurred in the oldest Paleocene.This led in Eocene time to increase in average size,larger mental capacity,and special adaptations for different modes of life.In the Oligocene Epoch,there was further improvement,with appearance of some new lines and extinction of others.Miocene and Pliocene time was marked by culmination of several groups and continued approach toward modern characters.The peak of the career of mamals in variety and average large size was attained in the Miocene.
The adaptation of mammals to almost all possible modes of life parallels that of the reptiles in Mesozoic time,and except for greater intelligence,the mammals do not seem to have done much better than corresponding reptilian forms.The bat is doubtless a better flying animal than the pterosaur,but the dolphin horse and the antelope must excel any of the dinosaurs.The tyrannosaur was a more ponderous and powerful carnivore than any flesh-eating mammal,but the lion or tiger is probably a more efficient and dangerous beast of prey because of a superior brain.The significant point to observe is that different branches of the mammals gradually fitted themselves for all sorts of life,grazing on the plains and able to run swiftly (horse,deer,bison).living in rivers and swamps (hippopotamus,beaver),dwelling in trees (sloth,monkey) digging underground (mole,rodent),feeding on flesh in the forest (tiger) and on the plain (wolf),swimming in the sea (dolphin,whale,seal) and flying in the air (bat).Man is able by mechanical means to conquer the physical world and to adapt himself to almost any set of conditions.
This adaptation produces gradual changes of from and structure.It is biologically characteristic of the youthful,plastic stage of a group.Early in its career,an animal assemblage seems to possess capacity for change,which,as the unit becomes old and fixed disappears.The generalised types of organisms retain longest the ability to make adjustments when required,and it is from them that new,fecund stocks take origin - certianly not from any specialised end-products.So,in the mammals we witness the birth plastic spread in many directions,increasing specialisation,and in some branches,the extinction which we have learned from observation of the geologic record of life is a characteristic of the evolution of life.
iv.According to the passage,the greatest number of forms of mammalian life is found in the.
