Often a phrase like "as it does" is used merely for emphasis. However, without having more context for your example, "belonging as it does" could suggest that the following statement ("has a gnarled skin") is linked to the rhinoceros belonging to the odd-toed set of ungulates. But an ungulate is a mammal with hooves, I believe that gnarled skin is not a necessary characteristic. The horse, for example, is an odd-toed ungulate. So, in isolation the sentence could be misleading.
I await the rebuttals from rhino experts.