[ValerieUSA]

produce fertile offspring

But could infertile offspring leave behind fossils just to confuse us???

[Polybius]

But could infertile offspring leave behind fossils just to confuse us???

Yep. Mules are an example. Horses and donkeys are close enough genetically to mate and produce offspring. However, the resulting offspring (mules) are infertile. Horses and donkeys are therefore classified as different species.

[Joe Driscoll]

Neandertals roamed across Europe.

Some things never change.