Hybrid Theory
The possibility of unknown monsters, also thought of as undocumented animal species, has been debated for many years. One of the ways people are explaining these creatures is with the theory of hybridization. Hybrid animals are a mix of two different species, and often look exotic, strange, or possibly, scary. Hybrids could explain sightings of so-called 'monsters.'
Mythological Hybrids
In mythology, many monsters are hybrids. These mythological creatures include the Hippocampus, a horse and dolphin cross, the Chimera, a hybrid of lion, serpent and goat, and the Griffin, which is a mix of lion and eagle.
Actual Possibilities
Many hybrid animals occur naturally in the wild, although it's not common. However, these hybrids are always crosses between very similar animals, such as a grizzly bear and polar bear cross, or a horse and zebra hybrid. Therefore, these animals look relatively normal, if more exotic than their non-hybrid relatives, and would probably not be thought of as monsters.