Why didn’t the small post apocalypse survivor dinosaurs just refill the niches? Did the asteroid alter the planet in some way fundamentally different than the prior 200M years?
Edit: (collaborative clarification with my 5yo, with paraphrasing): Birds are boring dinosaurs. Why didn’t the big dinosaurs (non bird) come back? Why are there no mammal-sized (non bird) dinosaurs? (e.g., mouse through elephant-sized or even whale size)
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I can’t find it, but I saw a theory that post Yucatan asteroid and resulting volcanic activity removed a significant amount of oxygen from the atmosphere – from around 30% to current 21% which made it hard for any large animals like the dinosaurs to take in enough in respiration to power their bodies.
Also, resulting dust in the atmosphere from volcanic activity and global cooling because of dust meant the evolutionary niche they filled non viable for life of their type.
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