The creatures listed below never existed, because if they did, they couldn't have lasted beyond one generation. It leads one to wonder how anyone actually thought they could have existed in the first place.
A lion's head on an ant's body. The ant's digestive organs can't process the raw meat that its lion head desires, and so the beast starves. How this thing survived long enough to procreate is beyond us, but it's little wonder you don't see them around anymore.
In the Tartar language, its name means "the vegetable lamb." This creature was native to the shores of the Caspian sea. It's a lamb that grows from a vegetable stalk and is forever connected to it, much like an umbilical cord. The creature is immobile, rooted to the ground like the plant that it is. When it eats all the grass within its radius, it starves.
An Ethiopian buffalo creature covered in scales. While that's pretty cool - and terrifying - in and of itself, the reason it makes this list is because it has an unhealthy inclination to eat its own legs. Now, at the risk of sounding insensitive, it's a fact of life that food shortages occur in Ethiopia - you'd know this even if your only source for topical news was reruns of South Park. But still - its own legs?! - how hungry do you have to get?
This scourge of Gibraltar and the Mediterranean is a carnivorous winged deer. When it flies overland, it casts a human shadow. We're fairly certain that Disney's Bambi would have turned out quite differently if Bambi's mother were one of these.
This horror from the Middle East is a ferocious yellow rabbit with a black horn atop its head. The horn is impossibly long, easily extending as far out as the creature is big. It's a wonder the thing can even stand, much less move. As if the horn weren't enough, it's also got big, pointy teeth. Please refrain from making Monty Python jokes.