A cruel example of Darwinism in action. The animals that are either slow to move, or weak, or previously injured, or otherwise stupid enough to just stand there are weeded out by speeding motorists, and those who survive crossing the roads live to breed offspring that are more likely to get out of the way when an SUV driver on a cellphone hits the gas pedal.
Roadkill is comprised mostly of rodents, turtles, deer. The rest is composed of domestic animals bred for aesthetics.
Squished cadaver that lies in or close to a road, most likely crushed or knocked by a passing vehicle. Is now rotting and being devoured and cannibalised by other animals.