The size of subarcuate fossa of six different mammals has been observed. Among the examined species; camel, dog, rabbit and rat show clear subarcuate structure, which was characterized by the shape of fossa, and could be easily measured by using endocast. In these species the parafloccular lobe of cerebellum is isolated from cranial cavity and engulfed by this fossa. However, in donkey, the fossa is unclear or absent. Studies have reported correlated relationship between the subarcuate fossa and the size of skull and the certain part of cerebellum. The size of the subarcuate fossa is varying from absence of the fossa to large size fossa with its high contribution area of skull size. Dog has the largest subarcuate fossa among the examined species in this study followed by rabbit then camel, after that rat, very small in ruminants and nearly absent in equine. The study reveals the possibility of subarcuate fossa to determine the degree of evolution of the animals, based on variation of this fossa in closely related animals. This order not follow any previous study in literatures that hypothesis correlation between the size of subarcuate fossa and the size of skull or animal size or even part of cerebellum which evolved in this fossa. The result of this paper supports the hypothesis of the correlation relationship between subarcuate fossa and phylogeny of the animals.