Читать книгу Spying on Whales - Nick Pyenson - Страница 11

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.

When viewed from the side, the top of a bottlenose dolphin’s skull is shaped like a scoop—if you were a dolphin, imagine having a skull with a dishlike forehead, right above your eyebrows. In life, for a dolphin this cavity contains a cone of fat called the melon, which gives toothed whales a domelike forehead. Tucked behind the melon, and underneath the blowhole, are empty sacks: air sinuses underlain by muscles and sealed with an organ that looks like a pair of lips. When these lips buzz like a trumpeter’s, they generate sound, which bounces around the inside of the head and then gets focused by the melon into a discrete path out of the head, as a high-frequency sound beam, like an acoustic beam emanating from a searchlight strapped to the dolphin’s forehead.

By coordinating this process across a specialized set of anatomical parts to generate sound, toothed whales create a form of biological sonar—or echolocate—to see their underwater world in sound. All toothed whale species alive today echolocate, whether they are sperm whales, beaked whales, river dolphins, porpoises, or true dolphins. It’s how they wayfind, or hunt, in murky rivers or at ocean depth, sometimes a mile deep, with no light. Echolocation itself has evolved only a handful of times in other vertebrates; toothed whales are the only animals that do it underwater.

Making high-frequency sound, however, is just one part of echolocation; after sound bounces off an object, it produces an echo that the animal needs to hear. (The classic dolphin chirps and squeaks are how they vocalize to communicate with one another at lower frequencies.) We can’t hear directionally underwater, but whales can because their ear bones float inside hollow pockets. In life, the ear bones of a dolphin hang in a sinus cavity full of spongy tissue, which acoustically isolates each ear, letting the brain detect small differences in the arrival time of sound between the right and left ear, helping to pinpoint the source in three dimensions. Whales have had the ability to hear like this since bthe time of Ambulocetus.

But how does sound get to the ear bones, especially when whales don’t have external ears? Fats are conductive of sound, and along with the melon, toothed whales have large, fat bodies that fit hand in glove into hollows in the backs of their jaws and then branch out, backward, into lobes that directly connect to the ear bones. Akin to the way our ear canals funnel sound, these fat bodies provide a pathway for sound to reach the ears, although researchers still debate whether there aren’t other acoustic pathways in the head—testing the anatomical basis for echolocation requires clever experimental work, and captive animals are not easily procured. This hallmark sense in toothed whales was poorly understood until the late 1950s, when scientists, supported by strong interest from the U.S. Navy, resolved the enigmatic echolocation abilities of toothed whales in a simple way: after covering a captive dolphin’s eyes with suction cups, they discovered that the animal was still able to navigate a maze to find a small object.

We still know little about how echolocation in toothed whales truly works, especially in wild, free-ranging animals. It surpasses even the best military technology, and we’re just starting to understand the basics. There is marked variation, from species to species, in terms of the arrangement of air sacs, melon shape, and even ear bones. What any one of those differences means for sound frequency and how whales perceive it remains a broad mystery, hopefully the work of future dissertations. We can say, however, that a quick tour of a dolphin skull shows us how evolution refashions or modifies existing parts—like nostrils displaced behind the level of the eyes—while other times it generates completely new structures, such as a biosonar apparatus on the forehead. How evolutionary novelty happens remains one of the most important unanswered questions in biology today.

Transformation and novelty are recurring themes in whale evolution as much as they are for any group in the tree of life, and it is sometimes difficult to parse the distinction between them. Consider how the feathers that most birds use today for flight are elaborations—transformed many, many times over—from basic scales that once covered their dinosaur ancestors. Or how turtles, early in their evolutionary history, acquired shoulder blades inside their rib cage; turtles’ ribs later fused with other bones so that every turtle thereafter, for the past 200 million years, has had a shell with its shoulders tucked firmly inside. In both of these cases, evolutionary novelty does come from somewhere in the body—it’s an extreme flavor of transformation that starts with some available parts—but novelty is different because of its consequences. Whereas a transformation can be the reduction of parts or a change in size or proportions, a novelty is a one-time evolutionary appearance of a new structure that enables the evolutionary success of all of its descendants. Today’s whales are exemplars of the great success of evolutionary novelty, with echolocation in toothed whales and filter feeding in baleen whales enabled by biological apparatuses present in none of their forebears.

Evolution is the intellectual glue that connects living whales, in all of their seeming weirdness, to their deep ancestry, which is both incomplete and still not entirely known. Skulls point us to these evolutionary clues in a tangible and clear way; and without these insights, and the millions of years that brought these changes about, it would be very hard to illuminate the connection whales have with other closely related mammals.

My way back to whales, as a scientist, has always involved skulls in one way or another. In college I puzzled over a half-rotten dolphin head when our field class, on a barrier island off the coast of Georgia, discovered its carcass buried in the sand. The putrid smell dispersed the rest of the class, but I held fast. I wasn’t riveted by the grotesque allure; instead I was captivated for the first time by the thought of how, exactly, a whale might become a fossil.

In graduate school, I sought fossil whale skulls peeking out of seaside cliffs or crumbling out of rock formations in badlands that were once seafloors. Cetaceans became my vehicles for understanding life over geologic time, across scales so vast that we cannot truly comprehend them, even if paleontologists casually discuss geologic markers as if referring to last week’s dentist appointment. And it all led me to the Smithsonian, where I tend to the world’s great collection of fossil whale skulls.

However, part of the deal with being a museum scientist, especially at the Smithsonian, is that people ask you for tours. It’s more than a fair trade. First, I like giving tours. They give me an excuse to try out new ways to talk about ideas—the big ones, like the evidence for evolution and extinction—that not only excite me but also explain how whales came to be. Also, tours often involve children, and children are usually the toughest audiences of all, whether they’re whale huggers or fossil fiends. If I can figure out how to keep them interested, even for a short show-and-tell, then I think I’ve done my job. And who knows, I might even be convincing enough to ignite more than a passing interest.

My friend and colleague Megan McKenna first taught me about whale heads and their inner biosonar anatomy when we were both in graduate school, so when she brought her family recently for an early-morning tour before the museum opened, I was excited at the opportunity to settle a debt. Her four-year-old daughter was just a bit older than mine. The museum’s halls, especially when they’re empty, can be intimidating spaces, so I started slowly—I didn’t want to overwhelm or manufacture too much excitement.

As we walked into the Sant Ocean Hall, we stopped short underneath the imposing right whale model, and turned to face the eel-like skeleton of Basilosaurus, grimacing from above. Basilosaurus is an early whale several million years younger than Pakicetus and Maiacetus but it looks worlds apart in size and shape. Its dinosaur-sounding name literally translates from Latin as “king lizard,” in a nod to its serpentine, bus-length body. The first fossils of Basilosaurus were collected from the chalky marls of rural Arkansas and Alabama in the early nineteenth century. With a skull over three feet long, jaws bearing palm-sized, saw-shaped teeth, and individual vertebrae large enough to serve as stools, a Basilosaurus skeleton gives every impression of belonging to a sea monster—and its name has stuck, if only for the conventions that scientists use to name species.

Unlike today’s whales, Basilosaurus has a head that does not dominate its body, arms that crook at the elbows, and a surprising, diminutive set of legs that could never have supported its large weight on land. But Basilosaurus has an involucrum like all the other early land-dwelling whales, and its ear bones floated in a sinus space below its skull. Basilosaurus did not echolocate, nor filter feed, leaving it caught somewhat in an evolutionary middle ground for whale evolution: one of the first fully aquatic whales, completely unreliant on land, yet still carrying many of the biological apparatuses of its terrestrial ancestors.

A Basilosaurus tooth

As I walked with Megan under the skeleton, I pointed to its hind limbs and joked aloud about how they dangled like poorly placed, miniature landing gear. Megan then leaned down to her daughter. “Hey, Etta, Nick studies whale bones just like those ones.” Etta looked at me intently, mulling the assertion. “Why?”

I opened my mouth to deliver a canned response involving school, science, and curiosity, more boilerplate than authentic. I knew I could do better. I waited a few beats.

“Their bones all tell stories,” I said, “about where whales came from.” She glanced up at Basilosaurus looming from the ceiling, like a giant, flippered, macabre snake. “And if you become a scientist, you can learn to read them and know their stories.” I knew I had her attention. “But they sure don’t just show up here in the museum all put together,” I smiled. “You have to find them first.”