Animals communicate in a variety of ways and animals are capable of feeling emotions. Mammals (like dogs and humans) have very similar neural and hormonal responses to external stimuli because we have a shared phylogenetic history.
For instance, the same areas of the brain light up in humans and other mammals when we feel pain or stress. By in large we use the same hormones to send the same kind of information, the hormones in you elicit the same response in dogs.
The complexity of emotions in animals is difficult to quantify because:
They may express them in ways we cannot or do not understand, as they may use senses that we do not use or they may have senses that we don't know about. For instance, it was only recently found that elephants can emit low-frequency sounds, way below human hearing, and in this way they can communicate over very long distances.
We are capable of explaining our emotions through words, whereas we can only gain an understanding of animal emotions through their responses to [our] external stimuli. We may also measure hormone levels or perform brain scans. "Evidence for emotions in animals has been primarily anecdotal, coming from individuals who interact with pets on a regular basis. However, critics of emotions in animals cite anthropomorphism as motivating factor in the above suggestion. Much of the debates confusion centers around the difficulty in defining emotion and the cognitive requirements necessary to experience emotion in a similar vein to humans". So yes, anthropomorphizing emotions is taken seriously, however that does not prevent scientist from trying to quantify animal emotions in other ways.