Question 3: the correct answer is Dolphin. Got it right? Award yourself 1 point.
Question 4 of 10
How many hearts does an octopus have?
Why, in question 3: Which of these animals is a mammal?
The answer is dolphin. It breathes air through lungs, has warm blood, and nurses its young, like every mammal. The shark is a fish, the penguin is a bird, and the octopus is a mollusk, a relative of squids and snails.
How to recognize a mammal
The trait that gives the group its name is the mammary gland: females of all mammals produce milk for their young. It's also common to have hair at some stage of life; even the bottlenose dolphin is born with a few hairs on its snout, which fall out shortly afterward.
Dolphins and sharks look alike on the outside because they live in the same environment and swim in a similar way, but they are not close relatives. The difference shows even in the tail: the dolphin's moves up and down, while the shark's moves side to side.
Other mammals that live in the water include whales, seals, manatees, and otters. All of them must rise to the surface to breathe, and some whales can stay submerged for more than an hour.
Dolphins live in groups and cooperate when hunting. In Laguna, in Santa Catarina, dolphins and fishermen have worked together for generations: the animals herd schools of mullet toward the shore and make a movement that signals when to cast the net.
