I never learned much about evolution, so please do explain it like I’m 5
In: Biology
Things go extinct usually because their niche disappears. The environment can no longer support them after changing in some way, or other competition / circumstances make their survival strategy completely non-viable. Or, something out competes or overtakes them for their niche, or targets them specifically. So, the species disappears.
If things were to change again to make the species potentially viable, and the niche reappeared (or something very similar to it), it IS possible for something like them to evolve to re-fill that niche, but it could be a completely different species. Each species that arises comes from a species that already exists, by slowly diverging in their traits to better suit the niche. If we have no dinosaurs now, it’s unlikely to get dinosaurs again, unless for some reason their very specific characteristics are better suited than those of modern predators. And, since it’d likely be a lot longer of a stretch to go from birds or similar species to undergo enough change to become “dinosaurs” as we know them compared to just… having large canines / felines / herbivores, those niches are likely to remain dominated by modern species.
After all, it takes time to get good at fulfilling a niche. It works better if the niche evolves with your species, or said niche is empty–if it’s already filled, anything newly adapting to this niche is at a massive disadvantage often compared to species ALREADY very well suited to it.
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