In which of the following subclasses of reptiles,the skull has a solid roof?

Which reptile possesses a four-chambered heart?

Which class of vertebrates was the first to lead a completely terrestrial life?

In which animal is a heart with an incompletely divided ventricle found?

Given below are two statements:
Statement $I$: The class name Reptilia refers to creeping or crawling mode of locomotion.
Statement $II$: All organisms belonging to Reptilia have three chambered heart.
In the light of the above statements, choose the most appropriate answer from the options given below:

Which of the following lacks a tympanum?