whay are sponges considered to be an evolutionary deal end?

Answer 1

They are extremely primitive, so scientists speculate that have remained evolutionary unchanged for millions of years. Because they have not every diverged from their original form, they are considered at a dead end. However, this does not mean that they will never adapt or change, because an alteration in the environment can cause such an effect.

Answer 2

Crocodiles are also an evolutionary dead end. Failure to speciate in eons.