Dolphins weigh approximately 125 lbs. to 22,000 lbs. depending on the species, with the most popular dolphin species, the bottlenose dolphin, weighing in at 1,100 lbs. Although orcas are often called killer whales, they are actually the biggest dolphin in the world.
Another odd member of the dolphin family is the pilot whale. The smallest dolphins, when it comes to length, are the vaquita porpoise and the Hector's dolphin. Sadly, one species of dolphins is now considered extinct and that is the Yangtze River dolphin. All dolphins can live up to 40 years in the wild and orcas can live up to 70 years in the wild. In captivity, dolphins have been known to have a much shorter lifespan.
Dolphins are interesting species that sleep semi-consciously. The dolphin is unlike humans and cannot breathe subconsciously, but rather needs to be fully awake or conscious. To do this, dolphins will only sleep with half of their brain at one time. The other brain will remain awake to look out for predators and to continue breathing.
Dolphins also have interesting ways of communicating. They use a series of sounds such as squeaks, clicks and whistles. They also use a sonar process called echolocation, to learn about their environment and where prey is.