In the shallows of Florida Bay, the fish can be very difficult to catch. Dolphins solve the problem by creating V-shaped walls of mud,a fish trap. Caught in the jaws of the trap, the fish have no where to go, except up. (Video limited to U.S. & Territories.)

What will a group of dolphins make of the silvery rings of air produced by a bubble machine? (Video limited to U.S. & Territories.)

Killer whales use a herding call to cause discomfort and confusion for a school of herring, making the fish easy targets for a meal. (Video limited to U.S. & Territories.)

All cetaceans, including whales, dolphins, and porpoises, are descendants of land-living mammals. How did these terrestrial ancestors morph over millions of years into the whales and dolphins we are so familiar with today? Dr. Mark Uhen talks with PBS Nature about marine mammal evolution.

What do marine mammals have in common with other mammals? What distinguishes them from other mammals?

Modern marine mammals include: Cetacea (whales, dolphins, and porpoises), Sirenia (sea cows and dugongs) and Pinnipedia (seals, sea lions, and walruses). All of these groups share limbs that are modified into flippers, and an overall streamlined body shape. Like all mammals, marine mammals are warm-blooded, give birth to live young, and mothers produce milk to nurse their young.

Most cetaceans also have some very sparse hair at some time in their development, but it is very much reduced compared to most other mammals. Unlike most other mammals, modern whales do not have external hind limbs, have their forelimbs modified into flippers, have extra vertebrae in their trunk and back, have flukes on their tails for locomotion, and have their nostrils at or near the top of the head rather than the tip of the snout.

Sirenians are similar to whales in that they have only sparse hair on the body. Also like modern whales, modern sirenians lack external hind limbs, have their forelimbs modified into flippers, and have flukes on their tails for locomotion.

Pinnipeds are semi-aquatic and all pinnipeds retain hind limbs. In pinnipeds, both the fore and hindlimbs are modified into flippers. Most pinnipeds retain a substantial coat of hair, although not all.

All cetaceans, including whales, dolphins, and porpoises, are descendants of land-living mammals. What do we know about their terrestrial ancestors?

We know from both studies of DNA and the anatomy of living animals and fossils that whales are part of a mammalian group known as the Artiodactyla. Modern artiodactyls include animals like cows, pigs, sheep, giraffes, camels, and hippos. Artiodactyls have many characteristics that distinguish them from other mammals, but the most distinctive of them are in the foot and ankle. First, artiodactyls reduce the number of toes such that the foot is symmetrical between two digits (a condition called paraxonic). If you think about a cow foot, the hoof seems “split” in two. These animals are often called cloven-hoofed for this reason. The foot actually isn’t split into two at all. Rather, it is actually two toes fused together. Second, artiodactyls have a bone in the ankle called the astragalus (which is found in other mammals as well), but in artiodactyls, it takes on a characteristic form with a pulley shape at each end. Early whales share these characteristics with other artiodactyls. The group of fossil artiodactyls that we think are most closely related to whales is called the Raoellidae, and they lived in Indo-Pakistan, China, and Mongolia during the early and middle Eocene. These animals were probably omnivorous, and some people think they foraged by walking on the bottom of bodies of water.

Around what time period did this terrestrial ancestor begin its transition back into water?

The earliest whales are known from India and Pakistan from around 52.5 million years ago, during the early Eocene.

How long did it take for this land mammal to morph into the whales and dolphins we are familiar with today? What were some of the key adaptations that took place and do we know the order in which these adaptations occurred?

Cetacean Evolution. Graphic by Karen Brazell.

How has their evolutionary story driven their behavior, for instance, in developing societies and communication skills?

It is very difficult to answer the question of what drives evolution. It is also probably not the right question to ask if you know how evolution by natural selection works. Basically, many offspring are produced, and only a few survive to adulthood and reproduce. Those that are best able to cope with the living conditions in which they find themselves will be most successful in terms of having the most offspring. Thus, evolution by natural selection is constantly changing species as the conditions in which they live change. So, there usually isn’t some driving force behind evolution, there is just the change in species as a response to changing conditions. That said, some whales, particularly the toothed whales and even more particularly the dolphins have evolved very large brains and are also highly social animals. These large brains and the sociality that appears to be associated with them must offer some kind of advantage over those without it.

When did whales break into the different suborders: Odontoceti and Mysticeti? What are the primary differences between these two suborders?

The earliest known member of the Mysticeti, the modern filter-feeding whales is from the latest Eocene, around 34 million years ago. The earliest known member of the Odontoceti, the modern toothed whales, is from the early Oligocene, around 30 million years ago. This suggests that the split between Mysticeti and Odontoceti occurred during the late Eocene.

What is the whale’s closest living terrestrial relative?

The closest living relatives of whales are the Family Hippopotamidae, which today includes the hippo, Hippopotamus amphibious and the pygmy hippo Choeropsis liberiensis. The fossil record of Hippopotamidae extends from the early Miocene to today.

When did scientists first propose that marine mammals evolved from land-living mammals? What findings led to this conclusion?

Ever since classical times, people knew that marine mammals were different from other sea creatures and they recognized some similarities with terrestrial mammals. Once scientists began to formally classify animals in the 17th century, whales, sirenians, and pinnipeds have all been recognized as mammals, but the placement of some of these groups (particularly whales) within mammals has been controversial until recently.

Were the cetaceans the only land-living mammals to return to water environments? If there were others, did they return to water during the same period and did they morph in similar ways?

There are only two groups of mammals (that we know of) that have become completely aquatic. These are the Cetacea (whales, dolphins, and porpoises) and the Sirenia (sea cows and dugongs). These two groups both originated in the early Eocene, and have followed rather similar evolutionary pathways, particularly in how their limbs and modes of locomotion evolved. This is despite of the fact that cetaceans are carnivorous and sirenians are herbivorous. In addition, the Pinnipedia (seals, sea lions, and walruses) evolved from a group of dog-like Carnivora in the late Oligocene. Pinnipeds are all semi-aquatic, coming ashore to breed and have their young. Another group called the Desmostylia evolved in the early Oligocene and lived until the late Miocene in the North Pacific Ocean. Desmostylians are thought to have been semi-aquatic herbivores.

Why did marine mammals go back to the sea?

It is difficult to answer the question “Why did marine mammals go back to the sea?” Remember that evolution by natural selection facilitates tiny changes generation by generation allowing those that function better in that particular environment to reproduce more often. That said, the earliest changes that we see in whales and some other groups of marine mammals involve feeding and sensory perception. It looks like these early terrestrial ancestors of these groups began feeding in the water and became more adapted to aquatic conditions over time.

What research is happening currently on marine mammal evolution?

New discoveries are continually being made by geologists, paleontologists, and modern biologists about the evolution of marine mammals. Geologists are constantly revising the age estimates of rocks in which we find fossils. New fossils are being described from Indo-Pakistan, North Africa, North And South America, Oceania, and Europe. This is an exciting time to study marine mammal evolution as many of the most important discoveries in this field have been made in the last 10-15 years, and there is no reason to expect that pace of discovery to slow down in the near future.

Mark Uhen is an Assistant Professor of Geology at George Mason University. Previous to working at Mason, Dr. Uhen was Curator of Paleontology at the Alabama Museum of Natural History, and Head of Research and Collections at Cranbrook Institute of Science. Dr. Uhen is also a Research Associate at the United States National Museum of Natural History.

In a Tanzanian jungle, a scientist and a medicine man follow a chimpanzee in search of a cure for a deadly disease. On the plains of Kenya, a woman learns a powerful lesson about family — from a pair of elephants. And in the Florida Keys, an eight-year old boy with a genetic illness utters his first words, for a chance to swim with dolphins.

From the ancient world to the modern, human lives have been influenced by animals in matters that reach far beyond the food chain. Wisdom of the Wild illustrates some of the surprising ways in which animals help teach, heal, and strengthen people, in body, mind, and spirit.

To order a copy of Wisdom of the Wild, visit the NATURE Shop.

Online content for Wisdom of the Wild was originally posted December 1999.

Join Hardy Jones in his crusade to protect dolphins in NATURE’s The Dolphin Defender.

Nearly three decades ago, filmmaker Hardy Jones became fascinated by wild dolphins. Even though many said it couldn’t be done, he set out to film these sleek sea mammals in the open ocean. Along the way, he became closely involved with his subjects and came to appreciate dolphins as highly intelligent creatures worthy of careful protection.

Eventually, Jones turned his camera into a tool for conservation. He filmed dramatic dolphin hunts, and the documentary footage made headlines and sparked international protests. Jones also discovered the effects of chemical pollution on dolphins and orcas, the largest species of dolphin. He came to realize that threats to these marine mammals were threats to the ocean itself, and to us all.

Now, in NATURE’s The Dolphin Defender, Jones shares some of his most dramatic and beautiful images, and tells the moving personal story of his journey into the world of dolphins. It is a memorable voyage revealed with the energy and elegance of the dolphins themselves.

To order a copy of The Dolphin Defender, please visit the NATURE Shop.

Online content for The Dolphin Defender was originally posted May 2005.

Fraser’s. Hector’s. Spinner. Rough-toothed. Bottlenose.

They are just a few of the nearly three dozen species of dolphin that glide through the earth’s oceans, at home in a watery world most air-breathing mammals would find hostile. But as NATURE’s Dolphins: Close Encounters shows, these small whales have proved remarkably rugged and intelligent. Indeed, people have come to admire these savvy athletes of the sea so much that dolphins have become the object of a billion-dollar entertainment industry. Each year, millions of fans pay to watch — and even swim with — their favorite animal. But the dolphin’s popularity also raises a troubling question: are these captive performers our willing partners — or our prisoners?

Like their close relatives the porpoises, dolphins are small whales that have teeth instead of comb-like baleen. But while porpoises have spade- or shovel-shaped teeth, dolphin teeth are sharp and pointy, perfect for grabbing a fish, crustacean, or squid. Like bats, many dolphins are apparently able to locate and home in on their prey using a kind of sonar, producing clicks and pulses of sound that bounce off the target. Some can dive to extraordinary depths, nearly one thousand feet below the surface, to find food.

The dolphin’s sonar and swimming prowess, however, aren’t the only traits that have made the animal so interesting to people. Dolphins also have social skills that have endeared them to mariners and fascinated scientists. Sea lore, for instance, is full of tales of dolphins that rescued drowning sailors by holding them up near the surface and pushing them to shore. Such stories, researchers note, may arise from the fact that dolphins do cooperate to help lift ailing relatives and newborns near the surface to breathe. And some dolphins do push floating objects around the ocean, for reasons researchers don’t fully understand.

In many ways, in fact, dolphins behave like people. They are highly social animals that often live in groups and take great pains in caring for their young. Dolphin mothers often babysit their calves for up to two years, until they are able to survive on their own.

But gaining insight into the lives of wild dolphins, which often live hundreds or thousands of miles from shore, has been difficult. There are places, however, where the conditions are just right for studying wild dolphins. One is Australia’s Monkey Mia beach. Here, as Close Encounters shows, clear waters and remarkably tame dolphins have allowed researchers to get close to their subjects.

For more than 30 years, the wild bottlenose dolphins have been visiting the remote beach on Shark Bay about 400 miles north of Perth. Most mornings, small groups of dolphins — which are well-known to residents by markings on their dorsal fins — swim in to snack on fish offered by visitors.

While the feeding is carefully regulated to prevent the dolphins from becoming overdependent on the human handouts, the practice has helped draw hundreds of animals to the Bay that aren’t frightened by people. As a result, Monkey Mia has become one of the most active dolphin research centers in the world. Since the 1980s, dozens of researchers have traveled to the area to study everything from mother-calf relationships to dolphin dating.

These studies have added much to our understanding of dolphins. Some researchers, for instance, showed that dolphins can use tools — a skill that at one time only humans were believed to possess. At Monkey Mia, the tool is a sea sponge, which the dolphins carry in their beaks, apparently to help stir up food from sea grass beds. Other scientists have tried to understand why some dolphins seem extremely attracted to pregnant women that visit the beach.

Still other studies, such as one by biologist Rachel Smolker, who is featured on Close Encounters, have examined dolphin speech patterns. Smolker and colleague John Pepper found that young male dolphins on the prowl for mates form alliances that appear to be cemented by sound. At first, the two males will have very different patterns of squeaks and clicks. Over time, however, the duo will develop a single, unique signal, perhaps to help them let each other know when an attractive potential date appears.

At Monkey Mia and other dolphin havens, however, development and pollution threaten to disrupt the lives of dolphins. But researchers hope that their work will help fuel conservation efforts. “The more we know about dolphins’ social lives and their specific environments,” says Diana Reiss, a Rutgers University researcher, “the better equipped we will be to protect and preserve their diminishing coastal habitats.

Online content for Dolphins: Close Encounters was originally posted August 2000.