The Rise and Reign of the Mammals

• 303-307m ya - The Carboniferous Rainforest Collapse - The climate became drier, temperatures swung cold and hot, and the ice caps melted, eventually disappearing for good in the ensuing Permian Period.
• 252-251m ya - The Permian-Triassic transition. 90% of species were wiped out. Mega volcanoes erupted for several hundred thousand years. Animals that survived became smaller (the Lilliput Effect). By growing fast and reproducing earlier, they have a better chance of successfully making it through a mating season, ensuring that their genes are passed on in this harsh, mercurial world.
• 230m ya - First Mammals
• 201m ya - Start of the Jurassic - Dinosaurs got bigger, mammals got smaller. Mammals were better than the dinosaurs at being small.
• 145m ya - Start of the Cretaceous
• 125-80m ya - Cretaceous Terrestrial Revolution - Angiosperms, flowering plants appear and quickly take over 80% of the flora, bringing alongside them pollinators
• 66m ya - End of the Cretaceous, beginning of the Paleocene - an asteroid hit the Yucatan peninsula with the force of over 1bn nuclear bombs, punching a hole in the crust 40km deep and over 160km wide. Almost instantaneously, everything within about 1,000km was vaporized, and the nuclear winter lasted several years. About 75% of species, including all dinosaurs except birds, died out. Only disaster species survive in darkness and filth, small and omnivorous. Within about 375-800k years temperatures stabilized and ecosystems recovered, and mammals take over. Now birds get smaller and mammals get bigger

What Makes a Mammal?

• Three are three modern groups of mammals:
  • Placentals - The placenta acts as the baby's pantry, lungs, and excretory system at the same time
  • Marsupials
  • Monotremes
• Warm-bloodedness
• Hair likely began as a sensory aid (like whiskers, a display structure, or as part of a gland-based waterproofing system, and was later repurposed as a body coating to retain heat. Once an animal has a lot of hair on its body, it's a tell-tale sign that it is producing at least some body heat internally, and doing its best to keep it from escaping. Making heat is expensive. Iv you're going to run your furnace at full blast, you'll want to close the windows, too, lest your gas bill will become unsustainable.
• Small size, warm-blooded metabolism, and stronger and more efficient bites developed together as part of a package deal.
• Mammals can sustain running speeds 8x faster than lizards and can forage for food across larger areas.
• They have to eat a lot more calories than cold-blooded animals of similar body size, and they have to breathe a lot more oxygen.
• Mammals developed a secondary palate - a hard roof of the mouth - which divides the mouth from the nasal passage. Lungs could take in more oxygen.
• The dentary-squasmosal joint allowed a completely new, more efficient way of eating. By chewing their food to mush, early mammals could do most of the processing in the mouth, beginning digestion before the food hit the stomach.
• The first Triassic mammals developed the neocortex - becoming brainier as they became better chewers.
• Mammary glands - Feeding babies with milk gives a steady source of food and fosters a bond between mother and child, which is important for cognitive and social development. For lactation to work , the babies must have diphyodonty (two sets of teeth, milk and adult), a hard palate and a muscular throat for sucking.
• Milk and larger brains evolved around the same time.
• Ear bones are jaw bones that evolution repurposed for hearing.
• New types of molars grind and shear food - come from eating insects