Welcome to another “Evolution Events” episode. Today’s topic includes the evolutionary and modern differences between two similar-appearing cetacean groups, dolphins and porpoises. Have you ever wondered what the differences between these animals are? We are referring here to porpoises as belonging to the “Phocoenidae” family, where dolphins belong to a few families including the familiar, “Delphinidae”. These common names and their meanings may, however, vary amongst languages or countries.
With many of our Evolution Events, we suggest reading “What’s in a Name? Whales, Dolphins, Porpoises in Order Cetacea” to clarify groups.
Let’s begin by telling these two types of animals apart. Most generally speaking, porpoises have small, triangularly- shaped dorsal fins; dolphins have curved, rounded dorsal fins. Porpoises have triangular teeth with flatter tops, where dolphins’ teeth are more curved and pointed. A porpoise has a rounder, more blunt face whereas a dolphin has a longer, more elongated rostrum (snout). Dolphins are usually larger animals that are more streamlined (e.g. think bottlenose dolphin).
Within the family Phocoenidae, there exist two subfamilies of porpoise. Dolphins are sorted into a number of families including Delphinidae, Platanistidae, Pontoporiidae and Iniidae. Now listen carefully as we bring another significant term into this article….“Delphinoidea”. Hmmm…this sounds similar to the above “Delphinidae”, but it has a crucially distinct meaning.
Delphinoidea is a superfamily that encompasses a lot of animals, and not just some dolphins. Delphoinoidea holds two extinct families (we will not go into this detail here), Delphinidae (remember, a dolphin family), Phocoenidae (porpoises), Stenidae and Monodontidae. For our purposes, we will not discuss Stenidae but instead only reflect on Monodontidae. Monodontidae is the family that contains belugas and narwhals today; this group has an important connection to porpoise evolution!
Scientists believe that porpoises evolved/split off from this family, Monodontidae, about 15 million years ago during the Miocene time period. In the past, porpoises have been grouped with the oceanic dolphin family, Delphinidae. This is not correct and they are distinct from this dolphin family.
With the above being stated, it is important for us to remember that all cetaceans belong to Order Cetacea (whales, dolphins, porpoises), which only has two major scientific categories; toothed whales and baleen whales. Evolutionarily speaking, both toothed and baleen cetaceans evolved from land mammals. All cetaceans with teeth belong to Suborder Odontoceti. The Pacific white-sided dolphin and Dall’s porpoise are both odontocetes, for example. As per above, porpoises and dolphins vary significantly, but do share more as we become less specific in the classification system!
Both porpoises and dolphins can be found in riverine as well as ocean habitats. They may both travel in groups, however it appears that dolphin pods tend to be more permanently structured with significant social pods (e.g. think life-long orca families). Though, this is not to diminish the group capabilities of porpoises. For example, on our tours we have witnessed short-term hunting groups of several dozen to possibly several hundred harbour porpoise.
On a fascinating note, some species of both dolphins and porpoise can be predated upon by orcas, or killer whales. It is hypothesized that porpoises have evolved a unique tactic to avoid orca detection; communicating in higher frequencies than orcas can hear!
Article By: Alexa D., B.Sc. Naturalist with Five Star Whale Watching.
Barnes, L.G.. 2006. Evolution, taxonomy and antitropical distribution of the porpoises (Phocoenidae, Mammalia). Marine Mammal Science 1 (2): 149-165.
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