Paleocene and Eocene epochs
64.5 to 36.6 million years ago

64 MILLION YEARS AGO

A study of 500 metre-deep core samples from sediments along New Jersey's coastline by a team of scientists led by Professor Kenneth Miller suggest sea levels rose and fell frequently by tens of metres soon after the reign of the great dinosaurs had ended. Such fluctuations were only possible if the Earth was not free of ice at this time.
The team made this interesting discovery after studying the sediment type, the fossils it contained, and the changes in the amount of isotopes from different elements in different layers of the sediment core. (1)

64-50 MILLION YEARS AGO

With far fewer predators of the dinosaur kind roaming around nearly 64.5 million years ago, certain mammals became more curious and adventurous by leaving their burrows, trees, or other hiding places on a more regular basis to search for food. (2)
As these mammals adapted to the open environment, their bodies were able to evolve physically bigger over time. However, brain capacity would probably not have increased significantly until memory, visualisation and communication were understood by certain mammals as important to coping with an increasingly more competitive and changing environment, especially as food supplies dwindled over time and other mammals began competing for their share of the food and other resources.

Earth in the Middle Eocene period around 50.2 million years ago. Image © 1997 C.R. Scotese is available from http://www.geologie.uni-stuttgart.de/down/maps2/pl12.jpg.
One of the mammals that evolved a slightly larger brain were apparently tree dwellers living in the tropical jungles around the equatorial regions of the planet. The oldest known primate is a small animal called Purgatorius: it appeared around 65 million years ago eating insects and climbing around in the trees searching for food, and it had excellent eyesight, strong grasping hands and a relatively large brain size.

55 MILLION YEARS AGO

World temperatures rose by up to 20&#degC over a 20,000 year period around 55 million years ago. There is every indication extra volcanic activity and mountain-building was occuring at this time.
Over the next 5 million years, flowering plants diversified in numbers, allowing a greater number of insects to thrive and an extra source of food for the evolving mammals.

50.2 MILLION YEARS AGO

The Himalayas are born from the collision of India with the Asian continent.
Antarctica separated from the Australian mainland and moves southward, resulting in the Australian continental shelf suddenly dropping away and forming a massive 5 kilometre deep canyon wall. By 25 to 30 million years ago, Tasmania and South America separated from Antarctica.
Icesheets begin to appear on Antarctica, causing sea levels to fall. Tasmania appears part of the Australian mainland.

40 MILLION YEARS AGO

The end of the Eocene Epoch saw the birth of extensive mountain-building in the Andes in South America, the Himalayas in central Asia, and the Rockies in North America. Australia also had its fair share of mountain-building with the appearance of a few volcanoes along Australia's eastern coast.
In Europe, a few volcanoes and numerous hot springs appeared in a region we would call Germany. Some lakes were known to have released poisonous volcanic gases. If the gases exceeded a certan quantity, it can kill the animals. Much of the European continent is heavily forested to support the many unusual mammals of both the herbivore and carnivore types of this time.
As for the wildlife in Australia, they were mainly concentrated in and around the inland sea and numerous freshwater lakes in the central part of the continent. Furthermore, the animals were relatively large and unusual compared to what we now have in Australia today. It is these unusual animals that would form the basis of many great ancient stories for the Australian aborigines.
It is believed by scientists that birds were the dominant creature on land during this period of Earth's history. This is a world where birds would eat animals the size of large tree primates.
In the water, dangerous mammalian predators were plentiful including the ancestors of the whales which existed in both lakes and oceans.

NOTES

The Canberra Times: Seas rising twice as fast - Global warming to blame: study. 26 November 2005, p.23.

Findings published in the 29 March 2007 issue of the research journal Nature suggests some mammals underwent a quick diversification and evolution after the dinosaurs died-out but the group of mammals that have survived to this day including humans began to diversify and evolve 10 to 15 million years after the apocalyptic event when global warming returned to heat up the planet.
The research was conducted by an international team of scientists including members of the Imperial College London and the Zoological Society of London. It involved studying existing fossil records. But because the fossil record is, by its very nature, incomplete, scientists had to apply new molecular evolutionary analyses to the fossil evidence by comparing the DNA of species and measuring the number of mutations. Generally, genetic changes are relatively constant over time. But since scientists can determine the common ancestors of today's mammal species, it is possible to measure the approximate time when extra mutations occurred for a species corresponding to a period of tremendous diversification and evolution.
Scientists also employed radioisotope dating to estimate the times for diversification from the fossil records as a means of supporting the molecular analyses technique.
After combining 2,500 partial evolutionary trees obtained through radioisotope dating and molecular analyses by other scientists, the first complete mammalian tree tracing the history of all 4,500 mammals known on Earth was created.
As Andy Purvis of Imperial College said:
"Our research has shown that for the first 10 or 15 million years after the dinosaurs were wiped out, present-day mammals kept a very low profile, while these other types of mammals were running the show. It looks like a later bout of 'global warming' may have kick-started today's diversity — not the death of the dinosaurs.
This discovery rewrites our understanding of how we came to evolve on this planet, and the study as a whole gives a much clearer picture than ever before as to our place in nature." (Highfield, Roger [Science Editor]. Global warming, not death of dinosaurs, led to rise of mammals: Telegraph.co.uk. 3 April 2007.)

The research has also discovered that many of the genetic ancestors of the mammals we see today existed 85 million years ago. Furthermore, the diversification came in two waves — one wave occurred around 95 million years ago, and a second major wave occurred around 50 to 55 million years ago (or roughly about the time when flowering plants diversified in numbers and types which may have provided a possible extra source of food for the emerging mammals).
World temperatures rose by at least 5&#degC (and probably closer to 20&#degC) over a 20,000 year period around 55 million years ago (the kind of temperatures humans might experience by the end of the 21st century).
Dr Kate jones from the Zoological Society of London added:
'Not only does this research show that the extinction of the dinosaurs did not cause the evolution of modern-day mammals, it also provides us with a wealth of other information. Vitally, scientists will be able to use the research to look into the future and identify species that will be at risk of extinction. The benefit to global conservation will be incalculable.' (Highfield, Roger [Science Editor]. Global warming, not death of dinosaurs, led to rise of mammals: Telegraph.co.uk. 3 April 2007.)