Question

Reptiles are classified on the basis of
(a)vacuities
(b)Brain
(c)Scales
(d)None of the above

Answer 1

Hint: The reptiles are classified mainly on the basis of the structure of their skulls, in which there are temporal fossae or empty spaces in the temporal region. The function of these temporal fossae is to enable the jaw muscles to protrude out onto the upper surface of the skull.

Complete answer:
Based on the number and presence or absence of temporal fossae or vacuities reptiles were formerly grouped under four sub-classes. The four subclasses are Anapsida, Synapsids, Parapsida, Diapsida.
(i)Anapsida-No temporal fossae. E.g., Cotylosauria, Chelonia.
(ii) Synapsida-Only lateral temporal fossae present. This group is believed to have given rise to mammals.
(iii)Only supra temporal fossae present.
(iv) Diapsida-Supratemporal and infratemporal fossa present.
Later studies on fossil reptiles made it clear that the above classification does not reveal the evolutionary or phylogenetic relation of the main groups. The terms Parapsida and Diapsida are now seldom used, though the names Anapsida and Synapsids are still retained. The more widely accepted classification is to divide reptilia into six subclasses, namely Anapsida, ichthyopterygia, Synaptosauria, Lepidosauria, Archosauria, and Synapsida.

Additional Information: -Subclass Anapsida includes extinct and living reptiles. The Temporal region has a complete bony roof.
-Ichthyopterygia includes wholly extinct aquatic Reptiles. Only supratemporal fossa present.
-Synaptosauria includes extinct aquatic and terrestrial Reptiles. Only supratemporal fossa present.
So, the correct answer is ' Vacuities'.

Note: -Reptiles are cold-blooded, lung breathing, oviparous tetrapods, with dry skin covered by the exoskeleton of epidermal scales, called corneocytes.
-The group is a heterogeneous assemblage, represented today by lizards, snakes, crocodiles, turtles, tortoises, and sphenodon.
-Reptiles are believed to be evolved from the carboniferous amphibian stock Ichthyostega, which existed about 360 million years ago. This significantly involved the evolution of shelled and amniotic eggs.