What type of evolution is shown in the figure?

Two morphologically similar populations are intersterile. They belong to

Assertion: From an evolutionary point of view,the human gestation period is believed to be shortening.
Reason: One major evolutionary trend in humans has been the larger head undergoing a relatively faster growth rate in the foetal stage.

Closely related,morphologically similar sympatric populations,but reproductively isolated,are designated as

Scientists believe that evolution is gradual. However,extinction,which is a part of the evolutionary story,is often 'sudden' and 'abrupt' and also group-specific. Comment on whether a natural disaster can be the cause of the extinction of species.

The phylogenetic tree of dinosaurs is given below. What do $P$ and $Q$ represent?