The chordate family tree shows the specific ancestors of vertebrates, and from an evolutionary perspective, vertebrates are phylogenically closely related to groups of animals called **tunicates and lancelets**.

Living chordate species are extremely diverse in population. In fact, up to date, the total number of vertebrate species living is around 96% of all the living chordates, accounting for a round 50,000 chordate species worldwide.

One major evolutionary trend of chordates is convergent evolution where groups of unrelated organisms obtain similar forms and functions due to similar environmental conditions.

The number of chordate species has changed over time, but during the course of evolution, it is evident that new adaptions can appear from one population species to another. For example, the presence of a jaw appeared first, because it can be used for effective feeding, then it was followed by paired appendages for locomotion.

Adaptive radiation occurs when a group of organisms diverges genetically due to changing environment. This is because the environment presents different challenges that must be solved by organisms. This rapid diversification leads to the formation of new species.

The web feet in both frogs and ducks are the result of convergent evolution because these organisms are not related but have similar organs. Recall that convergent evolution means that distantly related organisms have adapted similar traits in order to live and survive in their environment. The web feet are needed for both organisms to adapt to the aquatic environment.

See explanation.