Seal species and family

Like all organisms, seals are categorised into a family. All eighteen seal species belong to the same big family: Phocidae. The classification of all organisms is called taxonomy, which is based on phylogeny – the study of the relationships between species. This field of study is important, because it shows us how all living organisms are related to one another, how or when they might have diverged from another species, and which common ancestors they have. Take seals for example, they are closely related to sea lions and walruses. All three of these families are in turn grouped under Pinnipedia. These articles will examine the similarities and differences between these families a little more closely.

To better understand how the seal family is related to other pinniped families, it is important to understand their phylogenetic tree – or family tree. Seals belong to the order Carnivora, a group of mammals that must eat animals to survive.

After that, the seal family tree diverges into the Pinnipedia branch. These are all semiaquatic mammals that hunt for their prey in the water. They have flippers rather than paws and their relatively large, torpedo-shaped torsos are perfectly suited for aquatic life. All Pinniped families have in common that they have thick layers of blubber and very short tails.

The seal family includes eighteen species that are spread out across the globe. Most species live in the Arctic or the Antarctic, but there are also species that live in more temperate coastal waters. They spend most of their time in the water, only hauling out to rest, mate and birth pups.

This family comprises fourteen species of eared seals. The otariids are subdivided into two groups – the fur seals and the sea lions – which are visually and genetically very similar. The otariids inhabit the entirety of the Pacific ocean and the southern part of the Atlantic ocean.

The last family only has one member, all other members have gone extinct. When speaking of Odobenidae, it always concerns one species – the walrus (Odobenus rosmarus). Walruses are mostly found in the Arctic, but sometimes venture into subarctic areas.

Written by Aline Joustra, student Coastal Zone Management (University of Applied Sciences Van Hall Larenstein) and Wolter Stam, Marine Biologist

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R.R. Reeves et al - b, 2002. True Seals, Guide to Marine Mammals of the World (pp. 114-179). New York, National Audubon Society.
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