This era is mostly known for the start of all lifeforms to appear which could then give rise to developing into complex organisms to adapt and fully developed into magnificent beasts on land, air and some may return to the ocean once again. All life started from the oceans and were simplistic organisms as they had primitive behaviours on how they respond around their environment and other animals. Most of the Cambrian animals were filled with arthropods, invertebrates and chordates who we are most likely to be closely related that would rose to vertebrae organisms.

This era is known for the rise of terrestrial animals as few species of prehistoric amphibians (they still existed and thrived throughout the Permian until the Permian mass extinction the great dying  and lasted until Early Cretaceous) evolve to adapt to terrestrial lifestyle to handle the drier climate which lead to the reptiles. These reptiles were stem mammals, protosaurs and early ancestral reptiles to archosaurs that dominated the Permian ecosystem for 47 million years. One of the most iconic group of reptiles are stem mammals, these ancestral mammal relatives are more closer to mammals than reptiles but are not closer to us as animals such as dimetrodon had no direct relatives after its family group went extinct in middle of Permian, these ancient animals is where you can see the earliest sign of features that we would find in modern mammal today. Sadly, this era is not well known from the public as it is only well known from palaeontologists and prehistoric experts due to dinosaurs and ice age animals having more exposure and are generally seen as more profitable for companies to invest than trying to educate the public about prehistory. 

It is also known for the biggest catastrophe in our planet history called the Great Dying where 96% of all life went extinct. It almost caused the end of all life in our planet as all plant, terrestrial and marine life were badly effected from the disaster.

In Early Permian, it was cooler and humid after the end of carboniferous as it was still in ice age, there were polar regions covered with deep layers of ice in the south of Gondwana. However, they were tropical and sub-tropical climates that effected the rest of the middle and north of Pangea were covered in swampy forests. As Permian climate started to become more warmer, the glaciers started to receded and the continental interiors become drier due to increased of global warming. The climate were also seasonal as researchers characterized its unique climate as megamonsoons which means that it goes through extreme transitions between different seasons.

The climate near the end of Permian period were extremely hot and dry as deserts became more widespread in all landmass of Pangea due to global warming, the effects of increased volcanism could be the factor of unstable warm climate and the extinction of almost all Permian animals during the great dying or Permian-Triassic extinction event. Due to increased eruption of volcanoes, the ash covers the sky which blocks out the sun and stopped photosynthesis to occur for plant to thrive and produce deadly gases like Carbon Monoxide in atmosphere which caused deadly suffocation for all large terrestrial animals on land. 

This era is best known for the iconic and most researched dinosaurs that inspired pop culture and palaeontology that help us to understand about the evolution of birds/avian dinosaurs and, how adaptable and fascinating on how non avian dinosaurs thrived and dominated the Mesozoic era until the Cretaceous extinction. The Cretaceous was the longest and the most diversified era of Mesozoic. This era gave birth to new groups of animals, vegetation and microorganisms that existed in the Cretaceous that would one day will become more diversified and successful by the end of Mesozoic era to thrive in Cenozoic era. Specifically, birds/avian dinosaurs and mammals such as placental and marsupials evolve to thrive and find new ecological ways to adapt to their environment in Cretaceous era despite the large non avian dinosaurs and other Mesozoic animals such as pterosaurs and marine reptiles have already taken these ecological niches. Also, this era also spawn new ecosystems and environments to appear due to climate change and continental drifts for non avian dinosaurs, prehistoric archosaurs and smaller animals to adapt and diverse into new species to occupy these new ecological niches and environments. Also, the cretaceous climate started to become cooler in some part of the world such as parts of laramidia and Australia to create polar climate that causes the increase of harsh winters and precipitation so, the Mesozoic animals have to survive the long three months of harsh winter in colder climate. 

This era also helped tremendously for palaeontologists thanks to the abundance of fossils, transitional fossils and even almost complete or mummified specimens that give us better understanding about the animals anatomy, skin impressions, their true colours, fossilised content of foods in their stomachs and injuries that help us better understand about these species, it could even help us to understand about specific individuals life before their death. 

Ecosystem:

The Pleistocene (or known as Ice Ages) began around 2.58 million years ago to 11,700 years ago, this period is best known from high levels of interglacial climate and glaciers that been spread around the northern hemisphere. This period is also known for large megafaunas that exists around North America, South America and Eurasia such as mammoths, Sabre toothed cats, giant armadillos, giant deer's, giant sloths, even the last few terror birds that survived on this era and more. This was the coldest and harshiest era of our planet history that forces the animals to adapt quickly to unexpected climatic changes and endure the extended winters.

Throughout the Pleistocene, most continents were dominated by megafaunas who are bigger relatives of modern smaller relatives or extinct species/subspecies. The largest and most successful herbivores that occupy North America throughout the Pleistocene were mammoths and mastodons, they share the same behaviours and ecological niche as modern day elephant relatives in Africa. However, there were big difference between modern elephants. mammoths and mastodons, both mammoths and mastodons have huge woolly and shaggy coats to help them survive in the harsh cold climate while modern elephants have thick skin with small trains of hair. Mammoths and mastodons have smaller ears than modern elephants as it helps them from losing body heat. Mammoths are usually bigger than elephants and mastodons as mastodons have a shorter, stockier build and longer body than modern elephant.

There were also wild horses that roam and thrived in open plains that have similar behaviours and ecological niche similar to modern horses and zebras. They thrived throughout the North America open plains until climate change and human hunting have caused their extinction. In open plains, there were also aurochs, American bison's and American camels that share the exact same behaviours and adaptions of their modern relatives or subspecies. However, they were also immigrated animals that originated from South America and migrated to North America after the Great Interchange. There were glyptodon and ground sloths that managed to thrive and dominated their new environments as they resembled of the South American environments and their food supply to benefit them until the end of the Pleistocene due to climate change and human hunting. 

One of the most successful predators before the megafauna extinction in North America were sabre-toothed cats, American lions and scimitar-toothed cats. These big cats were able to thrived and dominated the North American ecosystems as there were able to become hyper specialized hunters to hunt large prey such as aurochs, wild horses, mammoths, mastodons American bison's and American camels. Some were solitary hunters like smilodon so they have to develop stronger hind limbs and large sabre-tooth to pin down their prey and use their large fangs to damage the prey throat to suffocate them. There were also pack hunters like homotherium where they strongly rely on pack members and endurance to chase down on their prey as they are good endurance runners due to longer legs and slender build. They hunt variety of prey such as pronghorn, aurochs, wild horses, mammoths, mastodons American bison's and American camels by chasing down their prey until they become fatigue and then pinned them down by using their hindlimbs and smaller canines. There were also American cheetahs that share the same ecological niche of modern African cheetah to hunt long distancing runners such as pronghorns but, there closest relatives were cougars or mountain lions so they convergently evolve to have similar characteristics to modern African cheetahs. They dominated the great plains until they went extinct during the end of Pleistocene due to climate change and perhaps human activity. There were also dire wolves which are one of the largest and most successful canines in the Pleistocene, they were the most successful and opportunistic hunters that specialized on hunting horses, American bison's, caribou and American camels. They share the same ecological niche and behaviours to grey wolves that also dominated during the Pleistocene and manage to survive in modern today, dire wolves were highly social pack hunting and sexual dimorphemic animals. They heavily rely on members of their packs to support each other in comfort, hunting and parental care so they can have more successful rate of producing new pups to continue surviving and thriving on their ecosystems.

One of the most dominant apex predators in the North America in the Pleistocene were modern bears and short faced bear. These massive and opportunistic hunters had variety of diets to help them survive in their ecosystem: modern bears have omnivorous diet so they eat berries, twigs, roots, grasses, fish, aurochs, wild horses, American Bison's and deer while short faced bear were strictly carnivorous so they hunted deer, musk ox, American bison's, wild horses, ground sloths and caribou.