Ontogeny recapitulates phylogeny
Dolphins and whales are mammals so they don't have gills.
Dolphins are mammals, not fish. And mammals breathe with lungs, not gills.
Mammals have lungs, as do amphibians, reptiles, and birds. Fish are the only chordates that have gills rather than lungs.
Monotremes are mammals; therefore they have lungs, not gills.
No, mammals don't have gills, and can't breathe under water. Mammals have lungs, breathe air and have to hold their breath when diving.
No. These animals are mammals, they breathe air.
No, sloths do not have gills. They are mammals and breathe air through their lungs like other mammals.
Mammals do not have gills. They rely on other respiratory organs, such as lungs, for breathing.
Sea otters do not have gills because they are mammals.
GillsThe gills perform the same function.
Mammals breath using lungs.
Gills are found in a number of animals. Most notably in all types of fresh and salt water fish but also mollusks like snails and slugs. Crustaceans like crab and lobster have them to as do a number of insects and amphibians such as frogs, lizards and worms.