Unfortunately that is a rhetorical question as there is many species of dolphins including the rather large orca (killer whale).
Dolphins are related to whales and porpoises.
Dolphins and porpoises are both cetaceans, and the term dolphin is usually reserved for the larger porpoise species, like the spinner and bottlenose varieties.
Whales and Porpoises are related to dolphins.
Dolphins and porpoises live in pods.
Porpoises are not actually dolphins, they are both different branches of sea mammals known as ceteceans but they are not the same so in answer to your question porpoises were not the first dolphin species on earth because they are not a dolphin.
The marine mammal related to porpoises is a dolphin.
Bottle-nosed Dolphin
All dalphin, porpoises, and whales belong to the order Cetacea.
Many people call dolphins porpoises. Though very similar, dolphins and porpoises are not the same.
No, dolphins, whales, and porpoises are mammals because they do not lay eggs.
Dolphins are marine mammals closely related to whales and porpoises.
Dolphins and porpoises are both cetaceans and are similar in behavior and overall appearance.