Dolphins never cease to amaze. As researchers delve into the underwater world of these brilliant cetaceans, we're learning how full of surprises these creatures are, from their intricate social lives to their intelligence. Here are just seven of the ways dolphins are exceptional, both physically and mentally.

Dolphins evolved from land-based animals

Dolphins didn’t always live in the water. They’re what’s called reentrants. Millions of years ago, the ancestors of dolphins roamed across land. The dolphins we know today are evolved from even-toed ungulates, which had hoof-like toes at the end of each foot. But around 50 million years ago, these ancestor animals decided the ocean was a better place to be. They eventually returned to the water and evolved into the dolphins that we know today.

The evidence for this evolutionary history can still be seen in dolphins today. Adult dolphins have remnant finger bones in their flippers, as well as vestigial leg bones.

Dolphins stay awake for weeks on end

Recent research has shown the surprising capabilities of dolphins for staying awake for days or weeks on end — or possibly indefinitely.

On the one hand, the ability makes perfect sense. Dolphins need to go to the ocean’s surface to breathe, so they can’t simply breathe automatically like humans do. They have to stay constantly awake to take a breath and avoid drowning. How do they do this? By resting just one half of their brain at a time, a process called unihemispheric sleep.

Brian Branstetter, a marine biologist with the National Marine Mammal Foundation, and fellow researchers conducted a test with two dolphins, seeing how long they could stay alert. According to Live Science:

The scientists found these dolphins could successfully use echolocation with near-perfect accuracy and no sign of deteriorating performance for up to 15 days. The researchers did not test how much longer the dolphins could have continued. "Dolphins can continue to swim and think for days without rest or sleep, possibly indefinitely," Branstetter told LiveScience. These findings suggest that dolphins evolved to sleep with only half their brains not only to keep from drowning, but also to remain vigilant.

Breathing and not being eaten are two excellent reasons to keep at least half of the brain active at all times. But what about baby dolphins? Turns out, they don't sleep at all either! For as long as a month after birth, dolphin calves don't catch a wink of sleep. Researchers think this is overall an advantage, helping the calf to better escape predators, keep the body temperatures up while the body accumulates blubber, and even encourage brain growth.

"Somehow these seafaring mammals have found a way to cope with sleep deprivation, facilitating rather than hindering a crucial phase of development for their offspring," UCLA researcher Jerome Siegel told Live Science.

A female dolphin with her calf. Neither of them are getting much sleep! A female dolphin with her calf. Neither of them are getting much sleep! (Photo: Jman78/iStockPhoto)

Dolphins can't chew

If you've ever watched a dolphin eat, you've noticed that they seem to gulp down their food. That's because dolphins can't chew. Instead, their teeth are used to grip prey. Sometimes, they'll shake it or rub it on the ocean floor to tear it into more manageable pieces. One theory for why they've evolved to do away with chewing is because they need to quickly consume fish before it can swim away. Skipping the process of chewing ensures their meal doesn't escape.

Dolphins have worked for the Navy since the 1960s

The idea of dolphins being employed by the military to scan harbors for enemy swimmers or pinpoint the location of underwater mines may seem like the plot of a B-rated movie. But it's true and has been for more than 50 years.

Since the 1960s, the U.S. Navy has been utilizing dolphins and training them to detect underwater mines. Much the same way bomb-detecting dogs work by using smell, dolphins work by using echolocation. Their superior ability to scan an area for particular objects allows them to zero in on mines and drop a marker at the spot. The Navy can then go in and disarm the mine. The echolocation abilities of dolphins far outstrip anything people have come up with to do the same job.

Dolphins are also used to alert the Navy to any enemies in harbors. Business Insider reports “The Navy Marine Mammal Program at the Space and Naval Warfare Systems Command (or SPAWAR) in San Diego, California trains 85 dolphins and 50 sea lions, according to SPAWAR spokesman Jim Fallin.”

There has of course been a good deal more speculated about the uses to which the military puts dolphins, including claims that they train them to kill people or plant explosives on ships. None of this has been confirmed by the military. Still, animal activists have long opposed the use of dolphins for military purposes.

Dolphins teach their young how to use tools

A 2005 study by researchers revealed that a population of dolphins living in Shark Bay, Australia use tools, and they pass that knowledge down from mother to daughter.

Individuals in this small group of dolphins will search for several minutes to find cone-shaped sea sponges that are shaped for the task. They tear this sea sponge free of the ocean floor, then carry it on their beaks to a hunting ground where they use it to probe the sand for hiding fish. The researchers think this helps protect their sensitive snouts while they hunt. The behavior is called “sponging,” and the researchers found it was not only the first instance of tool use in cetaceans, but it's also evidence of culture among non-humans.

According to National Geographic:

The hunting tactic was almost wholly confined to a small group of females and their daughters among the Shark Bay population, with just a single male showing the same behavior. The challenge for the study team was to find out whether sponging is acquired through social learning — and therefore evidence of culture — or is transmitted genetically. The researchers analyzed the mitochondrial DNA (DNA passed down by females) of 13 spongers and 172 nonspongers. They found the trait appeared to be passed on mostly within a single family line from mother to daughter and that sponging most likely originated in a recent ancestor.

It’s clearly culture, and a behavior taught by mothers to their offspring. It's another bit of evidence showing just how intelligent and social dolphins really are.

Dolphins have have several behaviors that are passed down from one generation to the next. Dolphins have have several behaviors that are passed down from one generation to the next. (Photo: Joost van Uffelen/Shutterstock)

Dolphins get high on fish toxins

We know that pufferfish have strong toxins. Apparently dolphins know this too, and they use this for recreational benefit.

Normally, pufferfish toxin is deadly. However, in small doses the toxin acts like a narcotic. BBC filmed dolphins gently playing with a pufferfish, passing it between pod members for 20 to 30 minutes, then hanging around at the surface seemingly mesmerized by their own reflections.

Reports The Independent: Rob Pilley, a zoologist who also worked as a producer on the series, told the Sunday Times: "This was a case of young dolphins purposely experimenting with something we know to be intoxicating … It reminded us of that craze a few years ago when people started licking toads to get a buzz, especially the way they hung there in a daze afterwards. It was the most extraordinary thing to see."

Apparently humans aren’t the only species to knowingly dabble in strange substances to achieve an altered state of mind!

Dolphins call each other by name

Dolphins have names and respond when called. Dolphins within pods have their own “signature whistle,” just like a name, and other dolphins can use that special whistle to get the attention of their pod mates. Considering dolphins are a highly social species with the need to stay in touch over distances and coordinate together, it makes sense that they would have evolved to use “names” much in the same way people do.

According to the BBC, researchers followed a group of wild bottlenose dolphins, recording their signature whistles and then playing the calls back to the dolphins.

"The researchers found that individuals only responded to their own calls, by sounding their whistle back. The team believes the dolphins are acting like humans: when they hear their name, they answer."

What's more, they don't respond when the signature whistles of dolphins from strange pods are played, showing that they're looking for and responding to specific information within whistles. The research opens up whole new questions about the extent of dolphin vocabulary and also could reveal clues about the evolution of our own language skills.

Jaymi Heimbuch ( @jaymiheimbuch ) focuses on wildlife conservation and animal news from her home base in San Francisco.