Final answer:
Paranthropus boisei was labeled as hyper robust due to its specialized skull and dental features geared towards heavy chewing, such as a prominent sagittal crest for muscle attachment and large, flat molars for grinding hard food.
Step-by-step explanation:
Paranthropus boisei was considered "hyper robust" due to distinctive features that indicate a specialization for heavy chewing. The most notable of these features is a pronounced sagittal crest, a ridge of bone on top of the skull that served as an attachment for powerful jaw muscles. Furthermore, Paranthropus boisei had a flat face with large jaws and large attachment sites over the entire skull for these muscles, as well as large, flat molars suited for grinding a diet primarily composed of hard nuts and seeds. This robust cranial and dental anatomy was a functional adaptation to its diet and is distinct when compared to their more gracile australopithecine relatives, who had a more varied diet and less pronounced masticatory features.