Question

these fossils of ancient animals were found in what is now asia and north america.
psittacosaurus, a 115 - million - year - old beaked dinosaur
protoceratops, a 75 - million - year - old frilled dinosaur
triceratops, a 67 - million - year - old horned dinosaur
protoceratops lived in what is now mongolia and china. like triceratops, protoceratops had a neck frill. unlike triceratops, the neck frill of protoceratops had large openings, which would have been covered by skin and muscles in life. also unlike triceratops, protoceratops did not have large facial horns.
many scientists hypothesize that protoceratops represents an evolutionary transition between beaked dinosaurs without horns and those with horns. which additional piece of evidence best supports this hypothesis?
protoceratops had more complex teeth than hornless beaked dinosaurs like psittacosaurus. these teeth were capable of cropping and shearing tough vegetation, similar to the more complex teeth of triceratops and other horned dinosaurs.
like other beaked and horned dinosaurs, protoceratops had powerful jaws, which it primarily used to process the tough plants it ate. however, it could also use its strong jaws to help defend against potential predators, such as velociraptor.
many dinosaurs, like duck - billed dinosaurs and long - necked dinosaurs, laid hard - shelled eggs. however, evidence from fossilized nests suggests that protoceratops likely laid soft - shelled eggs. the eggs of psittacosaurus and triceratops are unknown.

Explanation:

The hypothesis is about Protoceratops being an evolutionary transition between beaked dinosaurs without horns and those with horns. The first option shows Protoceratops has teeth complexity intermediate between hornless (Psittacosaurus) and horned (Triceratops) dinosaurs, supporting the transition. The second option is about jaw use (not evolution), and the third is about egg type (not related to horned - hornless transition). So the first piece of evidence best supports the hypothesis.

Answer:

Protoceratops had more complex teeth than hornless beaked dinosaurs like Psittacosaurus. These teeth were capable of cropping and shearing tough vegetation, similar to the more complex teeth of Triceratops and other horned dinosaurs.