They signaled the beginning of a revolution as they peeped out among the bushes. They were covered with fur and warm-blooded. Unlike their reptilian and amphibian counterparts, they could inhabit a larger region of the planet beyond the limits of their cold-blooded relatives. The Hellions were terrors of the air but being cold-blooded made them sluggish and vulnerable as the temperature dropped. Flying became more and more difficult and there was a point in the upper 40s at which they are not able to fly or digest food. In this state they were easy prey even for the smaller carnivorous mammals who brought a new hunting strategy to the table. They would simply wait for the temperature to drop until the reptile was sluggish then simply hunt as a pack while the hapless victim as an easy meal. This was basically the last major prehistoric revolution before the appearance of people and the Dimensional Merge that would forever change everything. The tropical garden had disappeared long ago and was part of the distant hazy past. The Bananasauros was dying out as it was not able to adjust to a changing environment.
In addition, they were also able to turn to scavaging if prey was scarce. These adaptable hunters played an important role in keeping the area clean and free of dead carcasses. There stomachs secreted a powerful acid that cold neutralized just about any bacteria found in decaying corpses. These same bacteria would have easily most of your other animals. The reptiles were now relegated to second class status as the newly evolved mammals gradually took over and changed the rules of survival. Of course during the hot summer, the Hellions still ruled the air and were unsurpassed as the top predator of the air. But being a flying reptile had its risks. If the Hellion suffered a major injury to its wing and was not able to fly it would gradually starve if it was not first eaten by other predators.
Smaller hunters in the patches of forest and meadows were quick to seize upon an opportunity for an easy meal. Another factor leading to the decline of the reptiles was the fact that their nests ran the risk of being raided by other more agile predators if they stepped away in a careless moment. These new mammals by contrast gave birth to live young and were able to find secure shelters to successfully raise their young. The faster these animals were able to adapt to their environment, the faster they would evolve. Or so it seemed. The evolutionary line for mammals seemed to diverge into several branches, as the process gradually travelled towards the poles away from the equator.