Ancestral traits (also known as primitive traits) are characteristics that are shared by a group of organisms because they have been inherited from a common ancestor. These traits are usually simple in structure and function, and can be found in other groups of organisms that are not closely related.
Derived traits (also known as modified traits) are characteristics that have evolved in a particular group of organisms and are not present in their ancestors. These traits are usually more complex in structure and function, and are specific to the group of organisms that possess them.
The main difference between ancestral and derived traits is that ancestral traits are inherited from a common ancestor, while derived traits have evolved in a particular group of organisms. Ancestral traits are found in many different groups of organisms, while derived traits are unique to particular groups of organisms.