The answers you've been looking for. The answers you've been looking for. Dolphins and porpoises are indeed classified separately by biologists, based on a number of criteria. Although the original classification was based on morphological differences between species, modern genetic techniques also tend to support the phylogenetic, or evolutionary basis for this classification.
Porpoises tend to have small, triangular shaped dorsal fins as compared to their dolphin relatives.
The dorsal fins of dolphins are taller and tend to have a greater curvature to their trailing edge.