The K–Pg event is one of the most drastic extinction events that had ever occurred in history. In geologic record, it is marked by a thin layer of sedimentary rock rich with the metal iridium, which is rare in earths’ crust but common in asteroids, suggesting that the event was caused by a collision with an asteroid approximately six miles wide. Another factor that contributed to the extinction is the eruption of the Deccan traps which released high quantities of sulfur dioxide. The layer of volatiles and debris in the upper atmosphere blocked sunlight; this meant that phytoplankton and plants could not conduct photosynthesis in these conditions. By the end of this event the mammals radiated and due to the lack of competition had dominated megafaunal niches ever since.
But in this timeline it was different, an increase in ammonia supported denser foliage cover, which resulted in a higher carbon dioxide intake, resulting in a glacial maximum. The deciduous trees began to be supplanted by graminoids, which can tolerate lower moisture and can regenerate quickly. The oxygen levels subsequently decrease after this event, inhibiting the development of large mammals, and enabling the avians, with their complex respiratory system to proliferate and efficiently compete with mammals. It began to cool once more during the Neogene, and the east Antarctic ice sheets began to accumulate until only the outermost fringes of the continent are ice free.
Format: Habitat, ancestor, diet
Example: Indian rainforests, Anthrasimias, insectivorous