AskHistorians

Given the data on human survival rates in collisions, high rate of speed is almost completely the causal factor of serious injury and death. So, at least for larger animals I would say it's a modern phenomenon. Maybe some rats or toads or something got hit by a wagon wheel but the scale would be nothing like today.

I read in this book that the "deer in the headlights" behavior is because they can't really process something moving at that speed.

I'm sure there were animals killed in wagon wheels and groups of people riding horses and stuff, but we're obviously on a different level.

Not roadkill per se, but most ancient societies had laws governing accidents caused by draft animals and carts. But I’d imagine they mostly took place in crowded urban streets, not rural roads with wild animals.