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 some of the ways dolphins are exceptional, both physically and mentally.
1. Dolphins evolved from land-based animals
Dolphins didn't always live in the water. They are 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 live. 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 and whales have remnant finger bones in their flippers, as well as vestigial leg bones. (For a quick refresher on homologous structures, the structures found in different species that originated from a common ancestor, read 8 uncanny examples of convergent evolution.)
2. Dolphins stay awake for weeks on end
Recent research has shown the surprising capability of dolphins to stay 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 said. 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 either. For as long as a month after birth, dolphin calves don't catch a wink of sleep. Researchers think this is an advantage, helping the calf to better escape predators, keeping the body temperature up while the body accumulates blubber, and even encouraging brain growth.
3. Most dolphins don't chew
If you've ever watched a dolphin eat, you may have noticed that they seem to gulp down their food. That's because dolphins can't chew. Instead, their teeth are used to grip prey, according to Whale and Dolphin Conservation. Sometimes, they'll shake their food 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 dinner can swim away. Skipping the process of chewing ensures their meal doesn't escape.
4. Dolphins have worked for the Navy since the 1960s
A Navy-trained dolphin wears a locating pinger as it performs mine clearance work in the Persian Gulf during the Iraq War. (Photo: U.S. Navy photo by Photographer's Mate 1st Class Brien Aho [public domain]/Wikimedia Commons)
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 decades.
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 any technology people have come up with to do the same job.
Dolphins are also used to alert the Navy to the presence of enemies in harbors. There has also been much speculation about other uses of dolphins for the military, including claims 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.
5. Dolphins teach their young how to use tools
Researchers discovered that a population of dolphins living in Shark Bay, Australia, use tools, and they pass that knowledge down from mother to daughter. The behavior is called "sponging," and the researchers found it was not only the first instance of tool use in cetaceans, but it was also evidence of culture among non-humans, according to research published by Eric M. Patterson and Janet Mann in the journal PLOS ONE.
Individuals in this small group of dolphins search for several minutes to find cone-shaped sea sponges. 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.
6. Dolphins form friendships through shared interests
This particular group of dolphins in Shark Bay have been keeping researchers busy over the years, revealing information about group culture and social habits.
Researchers from the universities of Bristol, Zurich and Western Australia discovered that the Shark Bay dolphins form friendships based on a shared interest — in this case, the sponge-hunting habit. This tool-using characteristic was found primarily in female dolphins, but by studying the behavior of the few male dolphins that exhibited the behavior, the researchers saw something new: relationships formed over shared tool technique.
"Foraging with a sponge is a time-consuming and largely solitary activity so it was long thought incompatible with the needs of male dolphins in Shark Bay — to invest time in forming close alliances with other males. This study suggests that, like their female counterparts and indeed like humans, male dolphins form social bonds based on shared interests," Dr. Simon Allen, a co-author of the study and senior research associate at Bristol's School of Biological Sciences, told Phys.org.
The researchers. findings were published in Proceedings of the Royal Society B.
7. Dolphins call each other by name
We know dolphins communicate, but we're learning more about how they do this all the time.
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, it makes sense they would have evolved to use "names" much 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 it also could reveal clues about the evolution of our own language skills.
8. Dolphins work together as a team
More recent research takes this idea of cooperative communication even further. A team of researchers from Bristol University found that male dolphins don't just synchronize their calls; they work together as a team, and attribute previously thought to unique to humans.
In describing the behavior of male dolphins as they work together to herd female dolphins, the researchers saw cooperative rather than competitive behavior, which is especially unusual in terms of finding a mate.
“The males aren’t attracting a female here, they have her, they are herding her,” Dr. Stephanie King, co-author of the study, told The Guardian. The team's findings were published in the journal Proceedings of the Royal Society B.
9. 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.
Rob Pilley, a zoologist who also worked as a producer on the series, was quoted in The Independent: "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.
Editor's note: This story has been updated with new information since it was first published in June 2016.