Centuries ago before scientific methods became commonplace, people used to believe anything including the existence of weird creatures. All it took was a narration by one lonely travel and just like that, you’ll have a new animal species.
But as eons have gone by, we’ve become better informed. We know that the following 10 animals never existed even though at one time they were believed to. 
1 Vegetable Lamb
In most myths, animals are either a combination of two different species or a bigger and more powerful version of those we already know. But the vegetable lamb was unique.
It wasn’t just an animal but also a plant according to some accounts of the myth. But other variations of this story state that the vegetable was largely a plant and instead of bearing fruits, it produced a lamb.
Just like you’d expect of any lamb, this had blood, bones, and flesh. The only difference was that it couldn’t move.
It was connected to its parent plant via a stem to its navel forming a sort of umbilical cord. The stem was flexible enough to allow the lamb to feed on the vegetation around the plant until there was no more to be eaten at which point both the plant and lamb would die.
Those around could then feast on the dead lamb whose blood supposedly tasted like honey. The wool on the other hand was used to make clothes, particularly head coverings.
Possibly, the myth might have been based on the cotton plant which despite being common in Central Asia was unheard of to the Northern Europeans before the 10th century. 
2 De Loys’ Ape
De Loys’ ape was thought to be a new primate species discovered in 1920 by FranŇ«ois de Loys, a big-time Swiss oil geologist. As the story goes, the geologist was out in the wild chilling with his friends near the Venezuela-Colombia border when they were attacked by a pair of monkeys. They shot at them killing one while the other disappeared into the jungle.
The monkeys were unique in the eyes of de Loys with his party because of their big size. So the geologist took a picture of the carcass but totally forgot about the whole encounter until years later when the photo was discovered by a French anthropologist, Georges Montandon.
The anthropologist was convinced that this was a never-seen-before ape and went ahead to create a new genus for it. According to him, it was an unknown American version of the orangutan, chimpanzee, and gorilla.
But when he was put to task at the French Academy of Sciences, he couldn’t defend his supposed new ape. Turns out the primate wasn’t unknown but a rather well-established species called the spider monkey.
3 Kraken
The Kraken is one of the most known mythical creatures since it was first imagined in the 12th century. It has its origins in the Nordic folklore and is believed to frequent the coasts of Greenland and Norway.
Today, it's featured in some of the most popular works of art like film, literature, and television.
The Kraken myth was only natural at a time when the sea was largely mysterious leaving a lot to speculation and a fertile breeding ground for embellished animal encounters. And just like most myths, the Kraken might have been a real-life animal blown out of proportion.
According to the myth, the huge monster was a deep-sea dweller and could ascend every few times to feed or attack ships. Owing to its huge size, it could cause massive whirlpools with its movement which will, in turn, capsize vessels.
After that, it’ll reach out with its massive tentacles to drag the ship below the surface and swallow it whole. The myth further alleges that there are just about two of these big guys since their massive size means the ocean would have been an insufficient source of food if they were to reproduce in large numbers.
In recent years, scientists have theorized that the Kraken could have been based on another real-life aquatic creature like a giant squid. Giant squids grow to as much as 10 meters and can weigh in at 700 kilograms.
4 Bonnacon
The renowned Roman author Pliny the Elder is credited as being the first to describe the bonnacon – a bull with a horse-like mane and inward-curving horns.
From the sound of it, the bonnacon is far much more normal than most of the animals you’ll encounter in mythology. But you’ll be mistaken to believe this.
Since its horns were backward-facing, it couldn’t use them to mount a good enough defense against attackers. So it had another perhaps more lethal weapon – its fecal matter. This wasn’t your usual waste material.
It was highly acidic and ensured the bonnacon’s safety by burning would-be pursuers.