What defining feature, associated with modern rhinoceroses, is completely missing in Paraceratherium?

Nasal horn

The most striking feature distinguishing Paraceratherium from most common perceptions of rhinoceroses is the complete absence of a nasal horn, which is a keratinous projection. This lack of a horn often prompts observers to question its familial placement, suggesting it might be an entirely separate evolutionary experiment in giant mammals. However, the fossil record indicates that the evolution of horns occurred at various times within the rhino lineage, and not all ancestral or contemporary species possessed them. Viewing the horn as the singular defining trait ignores the deeper millions of years of rhino evolution and the diverse adaptations that occurred before or alongside the development of prominent horns in later species.