Seals and sea lions belong to the group of marine mammals known as pinnipeds, which means "fin-footed" in Latin. While clearly related, the two species have a number of differences that make it easy to distinguish one from the other.
So Similar, So Different
Seals have stubby, furry front flippers with clawed toes and angled, non-rotating back flippers that makes them great swimmers but clumsy belly crawlers on land. Sea lions have larger front flippers covered in skin rather than fur. They can rotate their back flippers, allowing them to walk on land instead of crawling. Seals lack external ears and hear through a tiny hole on each side of their heads, whereas sea lions have small outer ears. Seals grunt softly when they have something to say, but sea lions are noisy barkers. In terms of size, seals are smaller than sea lions and are better adapted for life in the water. Compared to seals, the larger sea lions are party animals -- they can form herds with up to 1,500 members who like to lie together on a sandy beach to soak up some rays. Seals' preference for spending most of their time in the water fits well with their inclination toward a solitary lifestyle. They usually congregate on land only to mate.