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After The Dinosaurs - The Evolution of Modern Mammals

Sep 13, 2008
The extinction of the dinosaurs and the end of the Cretaceous period saw the start of the Tertiary period. This time leads right up until around 1.8 million years ago and the evolution of humans. The Tertiary is split into two main eras, the Paleogene and the Neogene, both of which are split into smaller time periods. These times would see the evolution and eventual domination of mammals, birds and insects as life re-evolved to fill the niches left by the departure of the dinosaurs.

Over the 42 million years of the Paleogene the Earth would change considerably. Continents continued to drift away from each other and into their current positions. Laurasia was still in one piece initially but Gondwanaland was splitting into what would become Africa, South America, Antarctica and Australia. India would eventually collide with Asia and form the Himalayas. After eight million years Laurasia was starting to break up into Europe, Greenland and North America.

It took just ten million years from the extinction of the dinosaurs for mammals to take over and evolve into larger herbivorous and carnivorous forms. The first mammals are considered quite primitive, with much smaller brain to body mass ratios than mammals that would appear later on. Little is known about them as remains are hard to come by, some are only identifiable from teeth fossils. By this point many of the main groups of mammals had their own evolutionary offshoots; platypus, marsupials, the now-extinct multituberculates and placentals were all abundant. However true modern mammals would not evolve until later, in the Eocene era around 55 million years ago.

By the middle stages of the Paleogene mammals had continued to evolve, with hooved animals, rodents, primates, bats and marsupials all present. By this point in time mammals had also taken to the seas. Animals such as Basilosaurus and Prorastomus would be early precursors to whales and seals.

The few reptiles that survived would go on to form modern turtles, crocodiles and pythons. The reptiles would never prove to be as dominant as they were in the Jurassic and the Cretaceous but adapted fairly well to the cooling Earth.

Flowing plants and grasses would come to dominate the plant world, with deciduous trees overtaking the tropical forests of before. Towards the end of the Paleogene era in the Oligocene legumes, ferns, roses, beech and pine trees had all evolved.

Birds continued to evolve and thrive in the new conditions. After the complete extinction of the Pterosaurs the birds had the skies to themselves and diversified into a great number of species. Cranes, hawks, pelicans, herons, owls, ducks, pigeons and woodpeckers all evolved during this time. Some of the most striking birds of the time are ones that have been dubbed Terror Birds. Flightless birds standing up to three metres tall and running at speeds of up to 30mph, birds such as Gastornis were the dominant predators in their ecosystems. These giant birds would struggle with the arrival of larger carnivorous mammals, and would eventually become extinct as they were no longer able to compete.

With mammals now dominating the planet, primates would continue to evolve and grow into new species. Over time one species of great ape would emerge as the dominant species on the planet, with its brain capabilities far outstripping any other organism before and since.
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