Scientifically the degu is called "Octodon degus". Degus are mammals, and belong to the group of "Rodentia"(rodents). More specifically they belong to the "Caviomorpha" (The guinea pig belongs to this group too). Within this group of "Caviomorpha" the degu belongs to the "Octodontidae".
Not long ago the scientific magazine "Nature"published an article about the "Caviomorpha". It said that "Caviomorpha" don't belong to the "Rodentia", because of the pair of extra teeth that they have. They are related to the "Lagomorpha" (to which belongs the hare) instead. If this is true, it would mean that the degu is not a rodent. But if you look at the degu , you will see that it doesn't look like a hare at all, but it much more looks like rodents. The degu's appearance can be a reason to decide that the degu is not a lagomorph. It is not clear to which group in the animal world the degu should belong. Some people want to create a new category for "Caviomorpha", next to the "Rodentia" and the "Lagomorpha".