"Extinction is not part of evolution. It is a failure to evolve."

Extinction plays a huge role in evolution. All species become extinct at some point allowing speciation to occur. Major extinction events such as the Cretaceous-Palaeogene event means a burst in speciation and allows entire new ecosystems to evolve, in this case the demise of non-avian dinosaurs that led to a rapid increase in mammal diversity and disparity, some evolving into giant forms.

Labelling extinction a failure is repeating an old trope we were all taught at school, but is the wrong way to think about extinction. Extinction is an inability to adapt and as an evironment changes, species become extinct. Look at the mass extinction we're causing on the planet now as we alter the environment organisms live in too quickly or simply slaughtering them en-masse; these species are not failing, we are.