Classification:
* Dolphins: Mammals
* Sharks: Fish
Physical Characteristics:
* Dolphins:
* Streamlined body shape
* Have a blowhole on their head for breathing air
* Possess flippers and a tail fin (fluke) for propulsion
* Warm-blooded
* Give birth to live young
* Feed their young milk
* Sharks:
* Cartilaginous skeleton (unlike the bony skeletons of most fish)
* Gills for breathing underwater
* Have fins for propulsion
* Cold-blooded
* Lay eggs or give birth to live young
* Do not feed their young milk
Diet:
* Dolphins: Carnivores, primarily eating fish, squid, and other small marine animals.
* Sharks: Carnivores, consuming a wide variety of prey depending on the species, including fish, squid, seals, and even other sharks.
Behavior:
* Dolphins: Known for their intelligence, social behavior, and playful nature.
* Sharks: Generally solitary creatures, though some species can form aggregations.
Habitat:
* Dolphins: Found in all oceans, as well as some rivers and estuaries.
* Sharks: Found in all oceans, as well as some freshwater lakes and rivers.
Conservation Status:
* Dolphins: Many dolphin species are facing threats such as habitat loss, bycatch in fishing nets, and pollution.
* Sharks: Many shark species are threatened by overfishing, habitat loss, and climate change.
Key Differences Summary:
| Feature | Dolphin | Shark |
| ------------- | ----------------------- | ----------------------- |
| Classification | Mammal | Fish |
| Breathing | Lungs, breathes air | Gills, breathes water |
| Skeleton | Bony | Cartilaginous |
| Temperature | Warm-blooded | Cold-blooded |
| Reproduction | Live birth, milk feeding | Eggs or live birth |
| Diet | Carnivorous | Carnivorous |
| Behavior | Social, intelligent | Solitary, predatory |
Remember that these are general distinctions, and there are many variations within each group.