Which of the following reptiles had huge fearsome dagger-like teeth?

The correct answer is Option (4) → Tyrannosaurus rex

Reptiles of many shapes and sizes ruled the earth for about 200 million years. The land reptiles among them were the dinosaurs, and NCERT names the biggest one and describes its teeth.

Option (1) Ichthyosaurs — Incorrect. Ichthyosaurs were land reptiles that went back into water and evolved into fish-like reptiles. NCERT does not describe them with dagger-like teeth.

Option (2) Stegosaurus — Incorrect. Stegosaurus is one of the dinosaurs shown in the family tree of Figure 6.2. It is recognised by the plates along its back, not by fearsome teeth.

Option (3) Brachiosaurus — Incorrect. Brachiosaurus, also shown in Figure 6.2, is the dinosaur with a very long neck. The book does not mention dagger-like teeth for it.

Option (4) Tyrannosaurus rex — Correct. Tyrannosaurus rex was the biggest of the dinosaurs, about 20 feet in height, and had huge fearsome dagger-like teeth.

NCERT Extract:
A Brief Account of Evolution – “… Giant ferns (pteridophytes) were present but they all fell to form coal deposits slowly. Some of these land reptiles went back into water to evolve into fish like reptiles probably 200 mya (e.g. Ichthyosaurs). The land reptiles were, of course, the dinosaurs. The biggest of them, i.e., Tyrannosaurus rex was about 20 feet in height and had huge fearsome dagger like teeth. About 65 mya, the dinosaurs suddenly disappeared from the earth.”

Figure 6.2 A family tree of dinosaurs and their living modern day counterpart organisms like crocodiles and birds