Subject: The difference between dolphins and porpoises

Lindsay J Porter (h9390327@hkucc.hku.hk)
Wed, 8 Apr 1998 12:21:19 +0800 (HKT)

>I was wondering what the differences were between dolphins and porpoises.

The terms 'dolphin' and 'porpoise' loosely refer to cetaceans of different
size classes - all 6 species of porpiose not exceeding 2.2m (although in the
USA there is a habit of referring to all cetaceans which are not whales as
porpoise, which has led to some confusion).  

Extracted from 
http://www.oit.itd.umich.edu/bio/Chordata/Mammalia/Cetacea/Phocoenidae.shtml

>Phoecoenids include 6 species placed in 4 genera. They are found in the
coastal waters of all oceans and seas of the northern
>hemisphere; along the coast of most of South America; and in some areas of
southeastern Asia. They are also known from a
>few Asian rivers.
>
>Members of this family are relatively small, from 1.5 to around 2 m in
length and up to about 120 kg in weight. They have
>short jaws and no beak. A dorsal fin is present and triangular in some
species, reduced to a ridge in others, and enormous in
>male Phocoena dioptrica. The flippers are fairly narrow and pointed. Some
species are conspicuously marked with black,
>white, and gray; others are uniformly colored.
>
>The skull is like that of the closely related delphinids, but it has
distinctive swellings on the premaxillae anterior to the nares.
>The facial depression is broadly expanded posteriorly and hides the small
zygomatic arches. The toothrows diverge
>posteriorly. The mandibular symphysis is relatively short, less than 20% of
the length of the ramus. The teeth are numerous
>(from 15/15 to 30/30), and distinctively spade-shaped with 2- or 3-lobed
crowns.
>
>Some phoecoenids (Phocoena and Neophocaena) generally occupy bays,
estuaries, and inlets close to shore. These
>porpoises are relatively slow, travelling in small groups of fewer than 6
individuals (occasionally up to 20). Others
>(Phocoenoides dalli) are found in offshore waters, are fast and agile
swimmers, and are sometimes found in groups of up to
>thousands of individuals. Phoecoenids feed on a wide variety of fish and
invertebrates.
>
The differences would appear to be minimal - I hope this information helps

best wishes
Lindsay J Porter
email h9390327@hkucc.hku.hk
Dolphin Research Group
The Swire Institute of Marine Science
The University of Hong Kong
Cape d'Aguilar
Hong Kong
website: http://www.webdivers.co.uk/dolphin/index.html