The Internet of things from its name enhanced field more than WSN and can connect these fields with each other to build new field, solve a specific problem or can be considered as a future work for any field in WSN or other field
For example, it can be used as a single research for secure WSN routing protocol like LEACH
But IoT is a network of anything based on the embedded sensors. Moreover, this network is usually connected to the internet and the whole data is saved and analyzed in the cloud storage.