60 million years ago, It's been at least 4 million years since the catastrophic extinction event that caused the disappearance of the giant dinosaurs and since then the vacant ecological niches have already been taken by large mammals. 

They've already quickly established their evolutionary success globally. Quickly outcompeting other animal groups for dominant roles...

The new era, the Cenozoic starts with the early Paleogene period, more specifically the Paleocene, the world is becoming to take the more modern look we are familiar with today, one big difference is the the subcontinent of India was in process of colliding into the Asian continent and despite how adaptive organisms have been, the world is still in the healing process, the planet is still being hit by frequent meteorites though no where near enough impactful as the ones that caused the recent mass extinction event.

The subcontinent of India was in process of colliding into the Asian continent that broke of from Africa and Madagascar. This gigantean continental sized collision will push up such landmass that it will form the largest mountain ranges of today, the Himalayas. 

While mammals are running havoc across the globe, here in Colombia, South America, mammals do not rule, and instead it's a land ruled by reptiles reminiscent of earlier times. Examples of such fauna are 40ft crocodilians and car sized turtles.

The most powerful apex predator here though is Titanoboa, a 14.3 m 1.5 tonne constrictor snake that descended from earlier boas that thrived under the shadows of giant dinosaurs is now of sizes similar to them, to avoid competition from crocodilians, Titanoboa's diet likely consisted of fish and probably rarely left water. Evident by the fact that it's curved teeth was not fused to it's jaws like that of modern boas that constrict large prey.

The Colombian environment that Titanoboa lived in was like that of today's Colombia, humid rainforests with large bodied rivers, flora was of low diversity and was still in the stages of evolutionary recovery and the absence of large Dinosaurs has allowed these jungles to become much more dense in vegetation, unlike elsewhere these habitats were hot and humid, reaching a high 34 degrees Celsius, it was the perfect opportunity for Titanoboa's poikilothermic ancestors to take advantage of and reach such gigantic sizes along side the fact there was little significant mammalian competition also had a role to play.

Due to the rich amount of biomatter these lush ecosystems sustain, they can cause the most dreadful hazard to all beings, the rivers that Titanoboa thrive in can build up of decaying biomatter, this matter of decomposing animal and plant material releases poisonous methane gasses, if these releases are sudden and big enough they can suffocate entire surrounding areas and kill nearby animals.

The rainforests Titanoboa was dependent on soon had intervals of disappearance, which in turn caused the disappearance of most of the giant reptiles that couldn't adapt quick enough to the change.

On the matter of methane releases, soon to come, will such gas releases will also occur in the oceans releasing mass quantities of greenhouse gases in the atmosphere, it events like these as well as predominately extreme volcanism that has already played a significant role on the impact on life of Earth that will cause total climate chaos to come, the Earth will soon receive a peak global surface temperatures, hottest the Earth will be through the entire Cenozoic, known as the Paleocene-Eocene Thermal maximum. To put it into perspective, the hot 34 degree rainforests of the Paleocene will be the entire average surface temperature of the entire Earth, such global heat will even allow the icecaps will be ice free and home to jungles.