Final answer:
Evolution of a new anatomical feature is considered a shared derived character, indicating new traits that arose from a change in genetic makeup and became prevalent within a group, representing a new branch on the evolutionary tree.
Step-by-step explanation:
From an evolutionary perspective, the evolution of a totally new anatomical feature (a derived character) is considered a shared derived character. This occurs when a change in the genetic makeup of an organism leads to a new trait that becomes prevalent within a group, representing a new branch in the evolutionary tree.
Over time, many organisms descend from this point and possess this new trait, which helps to identify more recent evolutionary relationships among species within a clade. This is different from convergent evolution, which refers to the process whereby organisms not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. An example of convergent evolution would be the wings of insects and birds, which allow the ability to fly yet evolved independently in these very different organisms. In contrast, a shared derived character, such as the amniotic egg in reptiles and mammals, tells us about the relationships among the members of the clade and suggests a more recent common ancestor.