Here's why:
* Massive Molars and Premolars: *P. boisei* possessed enormous molars and premolars, much larger than those of other hominids. These teeth were covered in thick enamel, ideal for handling tough vegetation.
* Powerful Jaw Muscles: The lantern jaw shape suggests strong jaw muscles, capable of generating the force needed to grind and crush the fibrous plant matter they likely consumed.
* Small Canines: Compared to its large molars, *P. boisei* had relatively small canines, further indicating a focus on plant-based foods rather than meat.
The "Nutcracker Man" Hypothesis: Scientists have nicknamed *P. boisei* the "Nutcracker Man" due to the specialized nature of its jaw and teeth, suggesting a diet heavily reliant on tough, fibrous plant matter, likely including seeds, roots, and tubers.
Important Note: While *P. boisei* is generally considered to have been a herbivore, some evidence suggests a potentially more diverse diet that may have included some meat, though plant matter likely remained the primary food source.