Can you be a bit more specific as to what you are comparing?
Marine mammals live and water and they need to surface to breathe. While land mammals can breathe just as humans do.
The average size of a whale's brain is larger than most other marine mammals.
The blue whale has the largest brain of any animal on Earth, including other marine mammals. It can weigh up to 20 pounds, which is much larger than the brains of most other marine mammals.
yes
The average size of a blue whale's brain is the largest among all marine mammals.
No. There are two different types of orcas. Residents eat only fish, transients will eat other marine mammals.
it is a branch off of marine biology that deals with whales and dolphins and other ocean mammals
All marine mammals and fish feed on other marine life to survive. Even the smallest fish in the sea feed on algae and plankton.
The big whales as a rule don't eat marine mammals, but Orcas - killer whales - will eat seals, sea lions, and even other whales when they have the chance.
Yes. Dugongs and manatees are marine mammals but unlike dolphins they are herbivores. Dugongs subsist on sea grass.
Any amphibian creature would be the obvious answer but I suppose most whales and marine mammals fall into this category as well. Sharks aren't scaly like other species of fish and so they'd qualify as well.
Platypuses and echidnas are different from other mammals because they are monotremes, i.e. mammals which lay eggs.