Q. What is an instance of a hypothesis which may explicate why there is not a big representation of the class Reptilia found in Polar Regions?

Beings of the class Reptilia are abundant and they are rare in intensely cold regions like close to the earth poles and more diverse in hot climate regions. They need an external heat source to warm their bodies and this is explicated because these animals are heterothermic that are they have "cold blood".

The heterothermic feature also explicate why reptiles are more active during the day, a period when they can use the sun heat to warm their bodies.