error message for index.cpp for polymorphism

index.cpp: In function ‘int main()’:
index.cpp:36: error: ‘unique_ptr’ is not a member of ‘std’
index.cpp:36: error: ‘unique_ptr’ is not a member of ‘std’
index.cpp:36: error: ‘animals’ was not declared in this scope
index.cpp:36: error: template argument 1 is invalid
index.cpp:36: error: template argument 2 is invalid