It was warmer on average, that’s true. It was still cold enough for snow and ice in some regions, though, so Pachyrhinosaurus probably would have seen some snow. What show said the Pleistocene was our first ice age? Sure, they’re relatively rare, and the last one occurred all the way back in the Permian, but saying ice had never existed is just wrong. More on reddit.com

The last ice age before the Quarternary ice age (current), Karoo ice age was thought to have occurred 360-260 million years ago, and the Mesozoic era lasted from 252-66 million years ago so it just about missed the major ice age. During the Karoo ice age ice caps were found in South Africa. During the Triassic period of the Mesozoic, the beginning, the climate was very dry and the interior of Pangaea was very dry and mainly consisted of deserts. The interior was very seasonal however, and there were periods of rainfall and humidity, because it is so far from the ocean which means it experiences temperature extremes. During the Jurassic, Pangaea began to split up into different continents meaning more land is in contact with the ocean. The temperature still was rising, but stabilised with less extremes. As more areas were near the ocean, deserts began to get smaller as humidity increased. The last era was the Cretacious and had very high levels of CO2 which meant the entire world had nearly the same average temperature. The average temperature was 10 degrees Celsius higher than today and the equator featured mainly deserts despite being close to oceans as the temperature was too high, even for most sea life to exist. So like today, the Earth had different climates. Areas on the inside of continents would have been deserts, and humid areas near the coasts or smaller islands would probably be jungles. More on reddit.com

Cretaceous, the era of go big or go home. It even ended like a boss. More on reddit.com

Triassic is good enough. "Our journey continues in the period denominated the Jurassic. The supercontinent of Pangaea has split into two landmasses - Laurasia and Gondwana. While not as arid as the Triassic, the climate is still hot and humid, with forests extending into the poles. Following a brief extinction event, out of literal ash, the dinosaurs rose like a phoenix, quickly dominating their environment in all shapes and sizes. Long-necked behemoths known as sauropods browsed above clashes between formidable carnivorous theropods and spiked stegosaurian prey. Flying reptiles known as pterosaurs patrolled the skies, and giant marine reptiles had their own dynasty. Their success will grant these species to rule some more million years, in which they will diversify even more." "Our journey ends in the Cretaceous period. Continental drift continues, as our world begins to take on a more familiar shape. The climate is still considerably warm. Dinosaurs remain in power, and have hit their evolutionary peak. Theropods continue their legacy with the largest carnivore to ever walk the Earth - Tyrannosaurus rex. Mighty herbivores known as ceratopsians fight for their survival with all numbers of horns. Some tiny dinosaurs have taken to the air, but live under the shadows of the biggest flying animals to yet exist. However, it was not to last forever. An asteroid the size of Mount Everest strikes near the Gulf of Mexico with the energy of 10 billion Hiroshima bombs. The impact unleashes global wildfires, in turn enveloping the planet in a firestorm. The ensuing 15-year period of freezing darkness would've finished off any survivors above 25 kilograms. Small, unassuming critters known as mammals, which previously lived in fear of the dinosaurs, were given the opportunity of taking their place. While this was the end of the dinosaurs' rule, it wasn't the end of their kind. One lineage of flying dinosaurs survived, rapidly diversifing in spite of the mammals' rise to power. They still exist with us today, where we now call them birds." More on reddit.com