Geologists and other scientists say more than 530 million years ago fishes were one of the first creatures to evolve into the Earth followed by insects which dwelled from 480 million years ago.
The two groups dominated sky, ground and sea but they failed to stop dynamics of evolution which brought reptilians about 320 million years ago. The arrival of these egg laying creatures brought many changes on the Earth’s surface due to their huge body size and a unique ability to multiply which gave them power against other creatures.
From that time reptiles spread into all parts of the world including forest because some of them were amphibians capable of hunting on ground, fly in the sky and retreat into the sea for their safety.
At the same time the world’s history shows that mammals evolved on the Earth about 320 million years ago but they were less known to other creatures until 250 million years ago when a mass extinction event killed 70 percent of vertebrates.
From an egg laying mammal, evolution of this group passed different stages but from those days to date their offspring start life without teeth to cut or grind food stuffs. Unlike fishes, reptiles and other creatures, from those prehistoric days to date mammals start their life without a well developed digestive system.
This weakness is clearly seen among, primates, antelopes and bigger mammals such as buffaloes and elephant which have digestive system which function using the same mechanism which is found among cows.
In order to get clear picture of how the mammary gland plays an important role on these animals it is better to see how their digestion system works. As we have seen the first chamber is Reticulum which has the main function of sorting out and blocks all unwanted materials from going into the second chamber.
Rumen is the largest chamber which is responsible for receiving all food from the mouth and store and makes it ready for the whole process of digestion. The third chamber in digestive system of a herbivorous mammal is called Omasum and this cavity is responsible for absorbing nutritious materials such as calcium and fat which are in liquid form.
During their early stage in life, it is the Abomasum or the fourth chamber where the main process of digestion and absorption of nutritious materials take place. Scientists say normally during their adulthood stage it is the rumen chamber is play major roles but calves of buffaloes, zebras and elephants start their lives while depending on the abomasums.
During suckling process saliva glands secrete large amount of special liquid which combine with milk from the breast to form a mixture which is taken direct into the abomasum. This chamber is equipped with special enzymes which are secreted purposely for digesting and absorbing nutrients such as starch, carbohydrates, proteins and fats.
The abomasum bears this crucial responsibility because from their embryo stage mammals grow up into their mother’s womb without a well developed diges tive system. Scientists use the word Viviparous for a process of giving birth without of a need of laying an egg which is crucial process which differentiates mammals from fishes, reptiles and birds.
Being one of prominent member of group of mammals, primate females en dure six months of gestation period which is rewarded with an infant which starts life while depend on supply of milk from its mother.
Cheetah, leopard, lion and other cats are born with blind eyes which force them to depend on their mothers for security during this delicate period. Despite their actions which terrify others in the savannah, these are mammals which start their lives in a humble manner just like a kitten of domestic cat which depends on its mother.
The tendency of starting life without having ability of eating normal food is a weakness which starts right from the embryo and redevelops into the birth stage where female mammals feed their offspring with milk from the mammary gland which scientists use it to name of this unique group of animals.
Scientists say all these came to be as mammals evolved into their full stage about 170 million years ago when they acquired a placenta which helps them to carry, protect and feed the embryo inside their bodies.
Meanwhile scientists say dinosaurs which dwelled on Earth for the first time more than 200 million years ago and conquered it for about 160 million before a long period of volcanic activities pushed them into extinction about 66 million years ago.
Scientists also say by wiping off most of these prehistoric giants the Earth opened its land to be inhabited by new creatures, these were the ancestors of modern birds which appeared about 150 million years ago by evolving from an ancient dinosaurs.
By using geometric properties of eggs which dates about 250 million years ago scientist say compared to modern birds some dinosaurs incubated their eggs for a long time with hatchlings being smaller and need more time to reach adulthood size, this slow, long and delicate reproductive resulted into their extinction 66 million years ago.
Scientists continue to say some species of aquatic birds and great ancestor of modern Cormorants dwelled on the Earth’s surface about 120 million years ago after they managed to escape extinction.
This was only possible when they started using eggs which were elongated and more symmetric than all other birds eggs but today cormorant lay eggs which are chalky blue in colour as special strategies to hide them against predators as they are incubated on trees, rock islets and cliffs.
Scientists say unlike modern ones, most of eggs of those days had ordinary size but were more porous a primary condition which allowed the exchange of adequate gas. This factor played an important role to the evolution of birds and reptiles at the time when the Earth was going through a dramatic climate changes which forced some creatures into extinction.
That was a crucial stage of evolution process which enabled some claver birds to bury their eggs in ground to protect them from volcanic activities which were blowing up from inner core as asteroids from the sky pounded its surface repeatedly.
Scientists say some birds such as quail evolved on the Earth’s surface more than 85 million years ago with strat egy of laying small spotted eggs which are less visible in the middle of grass where the small ground dwelling bird build their nestles.
It is believed that about 24 million years ago different geological and climate factors contributed into the expansion of the savannah grassland into different parts of the world including Africa where Serengeti, Tarangire, Mikumi, Ruaha and Katavi are known all over the world for being homes for mammals, reptilians and avian.
History indicate that ancestors of modern secretary bird evolved into the savannah about 23 million years ago before the earth passed through another climate changes which allowed some plants to evolved into huge forests and enabled some mammals to flourish.
This happened after the first land plant made its appearance about five million years ago then grew and multiply into a huge forest 90 million years later after the big bang which happened when planet Earth was being created about4.5 billion years ago.