Spying on Whales

Scattered around the peninsula are several islands like the one we approached, islands that served as barely inhabitable platforms for whaling operations in the early and midtwentieth century. Today the only remnants of human civilization are occasional concrete pylons with bronze plaques identifying the area as an open-air heritage site, and leftover whale bones. After we hauled our rubber boat up on the rocks, I walked toward the spoil piles of green-stained and weathered whale bones, strewn like spare lumber at a construction site.

Reading whale bones is what I do, although sometimes I feel like the bones find me. I’ve spent so much time searching for them, cataloging them, and puzzling over them that my brain immediately recognizes even the slightest curve or weft of bone. Whale bones tend to be relatively large, so finding them is often largely a matter of making sure that you’re in the right neighborhood—it shouldn’t have been much of a surprise, especially on the grounds of an abandoned whaling station. On the island I mentally inventoried the first assemblage I encountered, as I dodged foot-tall gentoo penguins scrambling at my feet: ribs, parts of shoulder blades, arm bones, and fragments of crania. They clearly belonged to rorqual whales, about the size of humpbacks, or possibly even fin whales. Some of the more intact vertebrae were artfully balanced upright on the shoreline, probably posed by Antarctic tourists, passing through the peninsula by the thousands in the austral summer and looking for a perfect photograph.

If these bones belonged to humpback whales, it would not be surprising, given the abundance of this species out around Antarctica today. It’s likely that some of the whales that we tagged were descendants of these individuals, belonging to the same genetic lineage. But history tells us that if you turned back the clock a century, humpbacks probably wouldn’t have been the only ones here: blue and fin whales would have numbered in the hundreds, if not thousands; minke whales, beaked whales, and even Southern right whales would also have been part of the community. Ari has seen only one right whale out of the thousands of whales that he’s observed over fifteen years in the area. Southern right whales have barely recovered from two hundred years of whaling, and we know little about where they go besides their winter breeding grounds along protected coastlines of Australia, New Zealand, Patagonia, and South Africa.

It’s not just right whales that vanished. There’s no memory or record of just how many of any kind of whale there was in the Southern Ocean, in terms of their abundance, before twentieth-century whaling killed over two million in the Southern Hemisphere alone. However, as whale populations in this part of the world slowly recover from this devastation, we’re beginning to see what that past world might have looked like. On an expedition in 2009, Ari and his colleagues documented an extraordinary aggregation of over three hundred humpbacks in Wilhelmina Bay, the largest density of baleen whales ever recorded. “There is no external limit on these whales because there is just so much krill. They literally cannot eat enough before they need to leave,” Ari reflected. “That incredible resource base means that it’s just a matter of recovery time for whales—and I think what we saw in the bay that year was a glimpse of what their world was once like, before whaling.” On the whole, humpbacks have recovered to only about 70 percent of their prewhaling numbers in the Southern Ocean, although along the peninsula their population size has nearly returned to the best estimates of prewhaling levels at the start of the twentieth century.

I paused on a guano-free ledge to record a few observations about the bones’ weathering and their measurements in my field notes. To the southwest, the sky churned in a dark gray, portending wind and snow, and I felt a chill creep into my damp toes and fingertips. I pulled off my gloves and reached for a disposable hand warmer in my jacket pocket. Lodged in a mess of receipts and lozenge wrappers was a note my son had left me on the kitchen counter back home:

Im gona mis you

wen you go to

anaredica.

The night before I left my home in Maryland we traced the expedition route on a plastic globe. When he wanted to know how far away eight thousand miles was in inches, I didn’t tell him the answer that I wanted to, which was “Too far.” I reassured him that the passage was safe and that we would stay warm. “I’ll think about you when we drink hot cocoa,” I offered, dressing up my own concerns with a good smile.

As we pulled away from Cuverville Island to return to the Ortelius, the swirling clouds began to send down flurries, covering us in thick, wet snow. The boat bumped hard against the waves, and we saw humpbacks surfacing far off in the distance, the wind pushing their blows quickly behind them. The sight of those living, breathing, feeding whales in the same view as the island with beach-cast bones made me feel as though I could see the present and past simultaneously, each telling us facts that the other vantage could not. The bones on Cuverville Island and Ari’s tagging work in the Gerlache were each a unique window into the story of humpback whales in the Antarctic, though these views were terribly incomplete: the past represented by mere bones crumbling on remote shores, what we know today limited to a few hours’ or days’ worth of data collected by a hitchhiking recorder on whales’ backs.

Scientists tend to operate within intellectual silos because of the years of training and study that it takes to know about any single part of the world. But the best questions in science arise at the edges. Ari and I both want to know how, when, and why baleen whales evolved to become giants of the ocean—Ari wants to know more about their ecological dominance today, and I want to know what happened to them across geologic time. The answer to the basic question about the origin of whale gigantism requires pulling data and insights from multiple scientific disciplines, which is another way of saying that we need the perspectives of different kinds of science—and scientists—to untangle the monstrous challenges of the nearly inaccessible lives of whales. That’s why a paleontologist like me was on a boat tagging whales at the end of the Earth: I needed a front-row seat to know exactly what we can hope to know from a tag. But answering the questions that most captivate me about whales requires more than just a single tag. It means wrapping my arms around museum specimens, handling microscope slides, paging through century-old scientific literature, and wading knee-deep in carcasses.

The wind sapped the last warmth from my already-wet gloves and whipped through openings around my hood as I held tight to the ropes on the gunnels. The first scientists to visit this place, over a hundred years ago, didn’t have the luxury of disposable hand warmers. They suffered more brutally than we can really imagine, with less certainty of safe return. In these narrow margins they must have wrestled with the tension that overcomes scientists in the field: the desire to apprehend something almost unknowable against the tolls of living a world away from civilization. I patted my son’s note, folded safely inside my jacket pocket. Hot cocoa sounded just right.

I was never a whale hugger. I didn’t fall asleep snuggling stuffed whales or decorate my room with posters of humpbacks suspended in prismatic light. Like most children, I went through phases of intense study: sharks, Egyptology, cryptozoology, and paleontology. The curriculum was loosely inspired by my small curio cabinet crammed with a bric-a-brac collection of gifts and found treasures: abalone shells from my parents’ friends in California and fluorite from a great-aunt in New Mexico sat next to trilobites and fossil ferns that I had collected on family trips to Tennessee and Nova Scotia (good fossils being hard to come by on the island of Montreal). My collection was a tangible means to escape, across geography and time, as I read ravenously about dinosaurs, mammoths, and whales under the tacit encouragement of my parents, professors who recognized this type of aimless curiosity.

During one of my immersive phases, I came across a distribution map that showed the location of whale species around the world. With my finger I traced the range of blue whales, the largest of all whales, as it went right up the St. Lawrence River, which bordered my neighborhood. I wondered about my chances of seeing a blue whale casually surfacing in the distance near my house. The thought of a local blue whale was a reverie that often arose in my mind as a kid, although it took two decades for me to return to it in earnest, as a scientist.

Some branches on the tree of life become quite personal, for reasons that are difficult to explain. We seek reflections of parts of ourselves in beings seemingly close to us—the disdain of a house cat or the perseverance of a tortoise—but in the end these species are distinctly other, refashioned by evolution and eons of time away from our shared ancestry. Those differences are accentuated to the furthest degree in whales; they seem mostly other—otherworldly, really—and that makes them both fascinating and enigmatic. They embody an incongruity that is vexing because they betray their mammalian heritage in so much of what they do, yet they look and live so far apart from us. Their size, power, and intelligence in the water are astonishing because they’re unparalleled, yet whales are benign and pose no threat to our lives. They are almost a human dream of alien life: approachable, sophisticated, and unscrutable.

I don’t malign whale huggers and dolphin lovers, even if I wrinkle my nose at the rhapsodic celebrations of armchair experts. Yes, whales and their lives are superlative, foreign, and well worth epic prose. But their amazing qualities are just starting points for me, as a scientist. Whales aren’t my destination: they are the gateway to a journey of discovery, across oceans and through time. I study whales because they tell me about inaccessible worlds, scales of experience that I can’t feel, and because the architecture of their bodies shows how evolution works. By rock pick, knife blade, or X-ray, I seek the corporeal evidence they provide—their fossils, their soft parts, or their bones—as a tangible way to anchor questions that surpass the bounds of our own lives. Whales have a past that reaches into Deep Time, over millions of years, which is important because some features of these past worlds, such as sea level rise and the acidification of ocean water, will return in our near-future one. We need that context to know what will happen to whales on planet Earth in the age of humans.

Whales are so very unlike the furry, sharp-eyed, tail-wagging, baby-nuzzling animals we think of when it comes to our mammalian relatives. First off, whales are among the few mammals that live their entire lives in the water. The only fur to be found on their bodies is the hairs that dot their beaks at birth. Although whales possess the same individual finger bones that you and I do, their phalanges are flattened, wrapped together in a mitt of flesh, and streamlined into bladelike wings, no hooves or claws to mar their perfect hydrofoils. Hind limbs exist only as relics in a handful of species, bony remnants tucked deep within muscle and blubber. A whale’s backbone ends in a fleshy tail fluke, like a shark’s; but unlike a shark or even a fish, whales swim by flexing their backbone up and down, not side to side. In short, they look nothing like squirrels or monkeys or tigers, but whales still breathe air, give birth, nurse their young, and keep company with one another over their lifetimes.

Fossils tell us the earliest whales were more obviously, visibly mammalian. The first whales had four legs, a nose at the tip of their snout, and maybe even fur (up for some debate among paleontologists, as fur doesn’t readily fossilize). They had sharp, bladelike teeth and lived in habitats that ranged from woodlands with streams to river deltas, occasionally feeding in the brackish waters of warm, shallow equatorial coasts. The oldest fossils of these land-dwelling, four-legged ur-whales come from rock sequences around about fifty million to forty million years old in the mountain ranges of Pakistan and India. At the time, the Indian subcontinent had not yet collided with Asia and sat in the middle of the forerunner to the Mediterranean Sea, called the Tethys sea, which split the Old World at the equator.

The skeletons of most of these first whales were the size of a large domestic dog. Because they lived on land, you won’t find the flattened arm and finger bones we see in whales today—instead their limb bones are round and weight bearing, and their hands and feet end in elegant, delicate phalanges. Their tail, as far as we can infer from the available bones, did not end in a fluke. Their Latin names give some clues about their provenance or what makes them special. Pakicetus, for example, originates from an area that is now Pakistan, but was once an island archipelago where early whales climbed in and out of streams. Ambulocetus, a low-slung early whale with body and skull proportions like a crocodile, has a name that translates as “ambulatory, or walking, whale.” Maiacetus, one of the rare early whales for which we have a near-complete skeleton, earned its name from fetal bones preserved near the abdominal cavity of the original specimen—the mother whale. Today’s whales all give birth tail first; the rear-facing position of the fossilized fetal Maiacetus showed that whales at this evolutionary stage still gave birth on land, headfirst.

The combination of four legs, phalanges, and cusped teeth is found in no whale alive today. What made these ancient creatures whales in the first place is subtle, lodged deep in their skeletons. That’s a good thing for us because these hard parts stand a chance of being preserved over tens of thousands of millennia. One of the most important features is the involucrum, a fan-shaped surface on the outer ear bone, rolled like a tiny conch shell. Pakicetus has an involucrum, as does every other branch on the whale family tree subsequent to it. The involucrum is one key trait, along with small clues in the inner ear and braincase, that the earliest whales share exclusively with today’s whales and no other mammals. In other words, it’s a feature that makes them whales and not something else. It’s unclear whether the trait gave Pakicetus an advantage for hearing on land, but later lineages of early whales co-opted it to hear directionally underwater, using a connection between the outer ear bones and the jawbones. Tens of millions of years later, the involucrum (and underwater hearing) persists in today’s whales, from porpoises to blue whales.

Pakicetus, a land dweller, swims in an Eocene streambed.

Fifty million years of whale evolution can be split into two major but unequal phases. The first deals with the transition of whales from land to sea in less than ten million years; the earliest land-dwelling whales all belong in that first phase—even at their most aquatic, they still retained hind limbs that could have supported their weight on land. The second phase covers everything that happened once whales evolved fully aquatic lives, for the remaining forty or so million years, until today. Throughout both of these phases, extinction dominates as a constant background theme because, as with the vast majority of animal lineages on the planet, most all the whale species that ever evolved are now extinct. While they are the most diverse marine mammal group today, numbering over eighty species, the fossil record documents over six hundred whale species that no longer exist.

The first phase of whale evolution is fundamentally about transformation: the tinkering and repurposing of structures from an ancestral state (originally for use on land) to a new one, in aquatic life. Transformation requires an initial state, and some starting points in evolution can be difficult to discern. For example, hearing, sight, smell, and taste are all senses that evolved for nearly 300 million years on land before the first ancestors of whales took to the sea. While it’s convenient to think of the reshaping of hands into flippers in whales as an undoing, that’s a mistake: whales didn’t undo 300 million years of terrestrial modifications. They did not, for example, recover gills. Instead, the story is far more interesting. Whales worked with what their ancestors had as land animals, modifying many anatomical and physiological structures for a new use rather than some phantasmagoric evolutionary reversal.

The second phase, after whales got back in the water, encompasses any whale lineage obliged to spend its life exclusively in the water; this phase also spans all of the consequences that arise from that constraint. You can think of evolutionary innovation as a hack on constraint. In other words, novelty in evolution is the appearance of a totally new structure, such as baleen, that confers not just a slight advantage to those who possess and inherit it but shifts their descendants into a completely new dimension of adaptation. The second phase of whale evolution, when innovations such as filter feeding and echolocation appear and fuel the diversification of today’s whales, stretches in time from the first aquatic whales, about forty million years ago, to the present day, including all living cetaceans, along with hundreds of extinct forms in between.

In the past 250 million years, many backboned animals converted from living in terrestrial ecosystems to living in oceanic ones. The first wave happened throughout the time of the dinosaurs, when many different reptile lineages invaded ocean ecosystems from 250 million to 66 million years ago. Since the mass extinction at the end of the Cretaceous, the ecologically dominant ocean invaders have been mammals—including everything from whales to sea otters—although penguins and Galápagos marine iguanas are also more recent reentrants. All of today’s marine mammal lineages are distantly related to one another, whether it’s a whale, a sea otter, a seal, a sea cow, or a polar bear (yes, technically polar bears too, which eat seals and hop across ice-covered seas).

What makes early whale evolution so important is that the completeness of the fossil record from the early stages—Pakicetus, Ambulocetus, Maiacetus, and all others like them during that first phase—is unmatched by any other group in the fossil record. We simply don’t have the range of fossils showing the specific anatomical transformations from land to sea for any other mammal or reptile the way we do with whale origins.

Even so, the evidence for whale origins has only recently been uncovered. Until about forty years ago, we had no idea what the hind limbs of the earliest whales in the first evolutionary phase really looked like. The discovery of Pakicetus in 1981 gave us mostly bones from the neck up—paleontologists discovered a small W-shaped braincase exhibiting, among other features, an involucrum, but it otherwise looked like any other land mammal’s. They found the skull—pinched and delicate, like a handheld vase—in river deposits, and concluded that the earliest whales lived some part of their life on land. Without more of a skeleton, at the time they could only speculate about what these whales looked like from the neck down.

In 1994 the discovery of Ambulocetus clarified this picture, showing that the earliest whales had weight-bearing fore and hind limbs, with separate phalanges perhaps connected in life by webbing. Relatively large feet in Ambulocetus were a clue about its swimming style, which likely involved flexing its spinal column along with its broad feet, in one motion. Mechanically this style is somewhere between paddling with hands and feet (using drag for forward motion) and employing a hydrofoil, as modern whales do with their tail fluke (using lift, instead of drag). Our pelvis is rigidly connected to our backbone, whereas in Maiacetus, the pelvis was only partially connected to the backbone, permitting a lot of flexibility for the whole spinal column to undulate up and down. The shape of a few tail vertebrae can reveal a lot about locomotion—in Ambulocetus the fact that the tail vertebrae are longer than they are tall tells us that these early whales had long, thickened tails, although we still don’t have enough bones to know what direction these powerful tails might have moved.

Ambulocetus still didn’t provide enough evidence to help answer the big questions about whale origins: Where did they fit into the mammalian family tree? Who are their closest relatives? By the 1990s, DNA studies had shown that hippos are the closest living relatives to whales. Hippos and other even-toed hoofed mammals, such as cows, deer, and pigs, are seemingly unlikely relatives, until you look at their stomachs. Even anatomists in the nineteenth century knew that living whales had multichambered stomachs like these ungulates, pointing to a possible evolutionary relationship. Paleontologists, however, had other extinct fossil mammals in the running for whale’s closest relatives: mesonychids, which had strikingly similar teeth and were wholly carnivorous, as whales are today, but left no descendants. Without more skeletal material from four-legged whales, especially from their limbs, there was no way to parse the stories of DNA versus fossils for the deepest origins of whales.

Then, in 2001, two competing groups of paleontologists reported the same pivotal piece of evidence from different species of early whales: they each had discovered that the anklebone of ancient land-dwelling whales was exactly like those of living even-toed ungulates. This bone, called the astragalus, looks like two 35 millimeter film canisters taped together like a raft; in your hand it feels like some kind of board-game piece. Cows, goats, and camels all have it. Living whales don’t because they have no feet, and the only traces of hind limbs are reduced to nubbins of bone next to free-floating pieces of their pelvis, wrapped deeply in their body walls—making fossil hind limbs in early whales the only source for this information. Mesonychids didn’t have these double-pulley anklebones, which meant their tooth similarities with early whales were the result of convergent evolution—something that has happened frequently in mammal evolutionary history. The discovery that early whales had a so-called double-pulley astragalus confirmed the DNA findings: whales were just highly modified even-toed hoofed mammals, minus the hooves.

Since finding Pakicetus, paleontologists working in remote parts of Egypt, Pakistan, and India have discovered a rich variety of early land-dwelling whales that lived about fifty million to forty million years ago, toward the end of a geologic epoch called the Eocene. These early whales seem to have been experimenting with ecological modes that have parts both familiar and strange: Ambulocetus looked crocodile-like; Maiacetus more like a sea lion, which had not yet evolved; still other strange early whales such as Remingtonocetus were an amalgam of zoological categories, something like a long-snouted otter; and Makaracetus, named after a mythological South Asian creature that is half fish, half mammal, had a downturned snout, perhaps for eating clams. All of these early whales belonged to extinct branches at the base of the whale family tree; our expectation about what makes a whale is hindsight biased, based on how we see them today—a great challenge paleontologists face when trying to understand the biology of these extinct whale relatives.

Knowing how whales turned out makes our retelling of their evolutionary pathway a tidy, preordained story. It’s easy to imagine Pakicetus, looking something like a lost dog dipping its toes in the water, followed then by intermediate stages of creatures each spending more time in the water: Ambulocetus, which could hear underwater and lunge at prey with its powerful limbs, like an ambush predator; followed by Maiacetus, whose pelvis was less strongly coupled to its spinal column, permitting the first kind of flexibility for tail-driven propulsion in whales. Fossils belonging to relatives of Maiacetus extend over a far greater geographic range than those of previous ur-whales, suggesting that this still-quadrupedal animal was seafaring, though it still returned to the shore to give birth, like sea lions today. In this view, Maiacetus represented the last of the earliest whales; all subsequent whales, in the second phase of the evolutionary chronicle, had no weight-bearing limbs and were totally separated from land.

The problem with this linear narrative is that we know the final result, which lets us pick and choose the likely path of least resistance toward the whales we recognize today. But evolution doesn’t work like that: it makes no concession for the future; it’s about what’s good enough in the moment. Selection operates on what’s available, sorting biological variation based on the demands of the immediate world. If you were somehow able to return to a late Eocene shoreline in the Tethys sea and happen upon the entire assemblage of early whales in one lineup—all of the early whales, four-legged and odd, scattered on the shoreline—you wouldn’t be able guess the eventual winner of the evolutionary sweepstakes. In its own time and habitat, each early whale was as well adapted as any crocodile, sea lion, or otter living today. It’s just that when we work with the fossil record, we’re afforded a view of the very long run, and the relative successes and failures in any particular group over millions of years. The eventual winners of the evolutionary sweepstakes were early whales that completely severed their ties to land, becoming fully aquatic, eventually yielding descendants that filter feed and echolocate.

These first whales were merely semiaquatic mammals with specializations for life near the water to one degree or another. There was nothing predetermined about some of their descendants becoming fish-shaped leviathans many millions of years later. Retrospection, however, does cue us into specific features that show incremental transformations: shell-shaped ear bones being repurposed for underwater hearing; or the pelvis becoming unlinked from the backbone, allowing the whole back end to serve as a propulsion device. If you focus on tallying which species go extinct and which ones survive, you might lose sight of the important lessons about major evolutionary change told through bones over geologic time.

Of all the two-hundred-odd bones in a whale’s body, skulls are probably the most important part to examine if you’re interested in the big picture of whale evolution. Like the skull of any vertebrate animal, whale skulls past and present conveniently house the primary organs for taste, smell, sight, sound, and thought all in one unit. Skulls are thus rich sources of functional information about the lives of whales and their transformation over time—after all, these senses are tweaked, enhanced, or diminished when lineages undergo major ecological transitions, such as the one from land to sea, over the course of evolution. Despite their durability, skulls are challenging objects for study. Their individual bones interlock with one another in complex and hidden ways, with blind corners, overlapping parts, and delicate connections. Soft tissues such as the eyes and brain all rest across several bones, like fruit sitting in a bowl made of interconnected puzzle pieces. To make things even more interesting, whale skulls are not only intricate but big. I’ve stared at whale skulls long enough that they feel familiar to me, but I always have to remember that whale skulls are, in very clear ways, unlike those belonging to any other mammal.

Take the skull of a bottlenose dolphin, which rests comfortably on a desk but would require two hands to move carefully. It consists of two basic parts: a paddle-shaped beak, formed of elongate bones with rows of teeth like pencil tips; and a cranium of layered bones that cover a bowling ball–shaped braincase. About those teeth: You won’t find the traditional lineup of incisors, canines, premolars, and molars that mammals usually possess. At some point in their evolutionary history, toothed whales gave up chewing for merely seizing their prey with a snap of their jaws and then swallowing it whole. A bottlenose dolphin may flash what looks like a welcoming toothy grin, but I wouldn’t put my hands anywhere near it.

Moving from the beak to the rest of the skull, the next-most-obvious feature is the orbit, the bone roofing where the eye would be, like a heavy eyebrow, still very much like that of other mammals. But behind the orbits, differences begin to accumulate. First, there’s the aperture that leads to nostrils, or the blowhole. You can peer down the curved passageway formed by these nostril bones to the underside of the skull, where you’ll see an origami construction of delicate, folded bones with paper-thin edges. The bones leading to the blowhole are actually behind where the eyes would be located, the complete opposite of any other mammal, where nostrils are located at the tip of the snout. If your nostrils were positioned like those of a dolphin, you’d blow your nose from the top of your forehead.

Pakicetus, Maiacetus, and Remingtonocetus had nostrils toward the tip of their snout, and these structures slowly migrated backward in other stages of fossil whales, up to the bottlenose dolphins that we see today, with nostrils displaced well behind the eyes. Interestingly, whales aren’t alone in nostril migration: sea cows and manatees, also full-time aquatic mammals, have nostrils positioned high on the skull (though not behind the eyes), whereas their early fossil relatives have nostrils positioned more forward. This parallel migration of the nostrils lets fully aquatic mammals, such as whales and sea cows, orient their body in a more energy-saving horizontal position in the water, as opposed to doggy-paddling with their nose out of the water. But swimming horizontally is just part of the reason for the strangeness of the bottlenose dolphin skull before us.