Question

what is the evolutionary origin of animals ?

type answer please :)

Answer 1

The term evolution originated from a latin word 'evolvere' meaning to unfold the hidden potentials. Evolution can be defined as change in properties of groups of organisms over succesive generations.Geological time scale is a record of geological events explaining earth's history. The geological time divided into era, period and epoch, which are further divided into different periods according to timescale and evolutionary sequence of organisams.

The first animal life is originated before cambrian period about 642-542 million years ago ( in the final stage of late proterozoic era, before cambrian peiod) the first  animal life 'Ediacaran biota' evolved from protists. They are soft bodied multicellular animals. The possibilities of existence of complex animal species even before ediacaran period cannot be ignored according to recent fossil studies.

Followed by this, during cambrian period, 542-488 million years ago, the diversification and proliferation of animals occured known as cambrian explotion.Most of the animal phyla existed today including mollusca, arthropoda, echinodermata, chordata etc originated during this time. The presence of trilobite, an arthropod was evident. Factors associated with cambrian explotion include presence of oxygen in the atmosphere, increased calcium level in ocean during cambrian period. Moreover there are several other factors expalined by theories that include environmental factors (such as ecological relationship between species, prey predator relationship etc) and genetical factors (evolution of hox genes facilitating morphological flexibility) which lead to historically unmatched diversification of animal kingdom during cambrian period.

Followed by cambrian period terestrail animals evolved during ordovician period. Continous environmental changes lead to masss extinction of species during permian period where trilobites disappeared. By the end of permian period, several reptiles disappeared while this lead to formation of new line of reptiles ie, dinosaurs by the end of permian period. Another mass extinction event occurred at the end of the Cretaceous period. Diversification of mammals and pollinating insects in cenozoic era. At the end of cenozoic era during quarternary period mass extinction of several mammals and origin of man occured.