Birds are dinosaurs — they never went extinct. When the asteroid hit 66 million years ago, non-avian dinosaurs disappeared, but their descendants (birds) survived and thrived. Beyond that, the survivors were surprisingly diverse.
Who Made It Through
- Birds — the only dinosaur lineage to survive. Small, fast metabolism, could survive on insects and seeds. Today there are 10,000+ bird species.
- Mammals — mostly small (rat to possum-sized). Could burrow, hide, and survive on insects, seeds, and carrion. Mammals then diversified into every niche left by dinosaurs.
- Lizards and snakes — some survived, especially small species that could hide. They recovered slowly over millions of years.
- Crocodilians — survived largely unchanged. They are apex predators that eat anything, flexible diet, semi-aquatic (protected from direct asteroid effects).
- Turtles — survived, especially aquatic species. Hard shells meant some could weather the initial chaos.
- Fish and amphibians — freshwater and ocean species survived better than land-based amphibians. The oceans took a massive hit but did not go sterile.
- Insects — the real MVPs. 99% of insect species survived. They are small, reproduce fast, and eat almost anything. Insects were the food base for everything else.
The Extinction Mechanism
The asteroid impact killed dinosaurs not through the impact itself, but through the aftermath: dust and soot blocked the sun for months, plants died, herbivores starved, carnivores followed. Large animals with slow reproduction died first. Small animals with fast metabolisms, hibernation, ability to burrow, or aquatic refuge survived. This is why the cutoff was roughly 25 kg (55 lbs) — anything larger than a large dog had almost no shot.
Pro tip: The extinction was not instant or universal. Some non-avian dinosaurs may have survived for 100,000+ years after the impact in isolated pockets, but they could not compete with the rapidly evolving mammals. The real story is not why some species died — it is why mammals and birds took over so completely after. They filled every niche dinosaurs left behind.