A publication that will remain anonymous here (since I hope to write for them one day), mixed up seals and sea lions on Twitter today. It’s easy enough to see why — they start off the same when you’re typing, and if you’re not paying attention, you’ve written one when you mean the other.
It probably also doesn’t help that they’re both marine mammals — pinnipeds, in fact — that look quite similar (seal on the left, sea lion on the right):
Sea lions and true seals (I’m going to ignore fur seals to make this a little less confusing) are separated by some 28.5 million years of evolution, according to TimeTree. The two animals are now in separate families, Otariidae (sea lions) and Phocidae (seals). There are many different species of both seals and sea lions, but all these animals have a basic, similar body shape: streamlined with flippers instead of feet.
But look closer and you’ll find subtle differences. The front flippers on seals are small, stubby, and hairy, with claws. Their back flippers don’t rotate but instead let seals be efficient swimmers. Sea lions have longer, skin-covered front flippers and back flippers that they can rotate underneath them, letting them walk, or at least shuffle about, on land. That makes sea lions the animals you’re most likely seeing basking on a rock at the zoo.
True seals sometimes have the name the “earless” seals because they don’t have anything covering the holes that lead into the hearing apparatus in their heads. Sea lions, though, have small flaps that cover their ear holes. There are also some differences in the whiskers, but I doubt many of us will ever get close enough to one of these animals to tell the difference.
Sea lions are also more vocal and more social than seals. Perhaps that means that sea lions are extroverts and seals are introverts.
Image credit: NOAA