What specific foot structure is Paraceratherium's limb arrangement derived from, despite its differences?

Basic three-toed structure

Although Paraceratherium possessed a limb proportion and toe arrangement that differed slightly from the standard modern three-toed rhino configuration, its anatomy demonstrates that it is clearly derived from the basic three-toed structure common to the Rhinocerotidae family. This alignment in toe structure, examined through detailed osteological studies, serves as crucial evidence tying it to true rhinos, differentiating it from other ungulates that might possess four toes, such as early relatives of horses. The retention of this underlying structural blueprint, even with modifications to support massive weight, confirms its placement within the established evolutionary trajectory of rhinos.