Sometimes things don't work out. Like the Edsel. Here's a bunch of extinct animals that didn't quite make it either.
Our favorite is the whorl shark, pictured here, who had a weird circular saw sticking out from its lower gum. With teeth like that you'd think, it would have been able to keep everybody else pretty far away. But time took him down too. (Its heyday was about 300 million years ago.)
The full list, with gallery, is on WebUrbanist, and shows a range of dinosaurs and other creatures that evolution didn't favor — at least not long enough that we got to meet them.
Some are familiar, like a 50-foot snake, or a four-ton fish as long as a school bus. Others are weirder, like the 8 and-a-half foot centipede-like thing, or the Macrauchenia, which looks like it was designed by a distracted deity who couldn't quite make up his mind: part camel, part horse, part anteater. It must have made Darwin (who discovered it) wonder how it lasted long enough for him to encounter it.
Images from WebUrbanist