Although they’re referred to as songs, male humpbacks technically are humming when they create their famous underwater compositions. The recital may contain half a dozen distinct themes that they’ve learned from other males, from one year to the next. (Video limited to U.S. & Territories.)

Analysis of one Amino acid in the Bowhead Whale’s tissue is revealing astonishing information about their age. There are some estimates that the whales could be over 200 years old, making them one of the oldest animals on the planet. (Video limited to U.S. & Territories.)

An infant sperm whale, separated from its mother, swims remarkably close to cameraman Doug Allan, and as it approaches, calls out with a series of loud coda clicks. (Video limited to U.S. & Territories.)

A group of male humpback whales compete for the affection of a female. After the female leaves and the mating marathon ends, the overlooked males engage in some surprising behavior. (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.

Humpbacks travel between Hawaii and Alaska every year, guided by their internal compass. The krill-rich waters of Alaska’s Alexander Archipelago are the whales’ summer feeding grounds, an environment very different from the calving grounds they have left behind in Hawaii. Here, more than the water temperature changes, the behavior of the whales changes, as well. While fiercely competitive in the breeding season in Hawaii, fighting for mates and protecting young, the opposite is true in Alaska. Whales cooperate, working in teams to gather food in the most efficient way possible. When the summer ends and the food is gone, mother and baby will head back to Hawaii again.

The young humpback calf has only a year to learn the subtleties of whale society before she is left by her mother to continue her education on her own, learning from observation and experience. It’s an incredible journey between two strikingly different environments that reveals the true complexity of the fellowship of the whales.

NATURE’s Fellowship of the Whales premieres Sunday, November 15 at 8pm (check local listings).

Photo © 2008 (Peggy Stap / Hawaii Whale Research Foundation) under NMFS Research Permit No. 587-1767-01

On the southeast coast of Australia, the town of Eden nestles along the shores of Twofold Bay. It was once a center of Australia’s thriving whaling industry, in part because it lies along the migration path of baleen whales swimming northward from the Antarctic. But residents say Eden’s whalers got some unusual help — from orcas, or killer whales, that patrolled offshore.

Locals such as Elsie Severs and Alice Otten who witnessed the hunts say the orcas took the lead in the hunt, herding larger migrating whales into the bay. Once the whales were confined in the bay, the orcas would then attack their quarry to the point of exhaustion. Human whalers moved in for the final kill — then shared the spoils with the orcas.

Discover this extraordinary story of interspecies cooperation on NATURE’s Killers in Eden.

To order a copy of Killers in Eden, please visit the NATURE Shop.

Online content for Killers in Eden was originally posted November 2005.

NATURE’s Humpback Whales follows these migrating marine mammals and presents their unique singing and hunting habits.

Graceful and magnificent, humpback whales inspire awe in young and old alike. These marine mammals travel great distances to take advantage of the best breeding grounds and feeding spots. North Pacific humpbacks, for example, mate and give birth in Hawaii and then travel to Alaska each summer to feed.

These gentle giants are famous for their singing abilities — belting out seductive ballads to attract mates or to challenge other would-be suitors. But they also have other talents. Their unique hunting skill, called bubblenet feeding, involves a group of humpbacks working together to capture schools of herring. Each whale has a particular role in the process: One whale swims in a circle while blowing bubbles under a school of herring. When the bubbles rise, the school of herring can not escape and form into a tight ball in the center. Other whales vocalize — grunting or screaming — to scare the herring to the surface. The whales then rise with their mouths wide open to capture large amounts of fish.

Trek across the oceans with these astounding creatures and discover more revealing details about their wonder-filled, watery ways.

Online content for Humpback Whales was originally posted January 2000.