The Walking Whales Read online

  and all modern and fossil cetaceans are characterized by the shape of one of the bones of

  the ear, the tympanic bone, shown here. (In cetaceans, the tympanic bone can also be

  called the bulla.) This bone has a thickened inner lip, the involucrum. In addition,

  modern toothed whales have a very thin wall on the outside of the tympanic bone: the

  tympanic plate. The tympanic bone cradles the middle ear cavity, in which the little bones

  (hammer, anvil, and stirrup, together called the ear ossicles) that transmit sound reside.

  their supposed land mammal ancestors,” a leading creationist, Duane

  Gish, wrote five years after the discovery of those fossils in 1985.3

  Whales have DNA similarities to artiodactyls4 (even-toed ungulates

  such as hippos, cows, and pigs), so they had long been considered the

  likely ancestors of whales. Gish ridiculed evolutionists for inferring

  from those molecular similarities that whales were derived from artio-

  dactyls. He dubbed the idea the “Bossie-to-blowhole” transition and

  called it an “udder failure.” As late as 1994, Gish called Pakicetus “a

  land mammal with no relationship to marine mammals.”5

  The tympanic bone of a whale (figure 2) looks like half of a walnut

  shell, a bowl-shaped bone with a central cavity. In addition, it has a very

  thick wall on one side and a very thin wall on the other side. The thin

  part is called the tympanic plate, and attached to it is an S-shaped crest

  6    |    Chapter 1

  of bone, the sigmoid process. The thick wall, known as the involucrum,

  consists of dense bone, much denser than that of other parts of the body.

  These are the critical characteristics of  a whale’s ear  bone, unique to

  whales  and  their  relatives,  dolphins  and  porpoises;  together,  all  these

  mammals are referred to as cetaceans.6 All cetaceans have a tympanic

  with an involucrum, and no other animal is known to have one. There

  are other features that are present in all modern whales and present in

  no other mammal, such as a blowhole, which is essentially a nose open-

  ing located way back on the forehead—but ancient fossil whales don’t

  have blowholes. Other features, including the S-shaped sigmoid process

  on the tympanic bone, are present in all modern and fossil cetaceans—

  but they aren’t unique to whales: some other mammals have them too.

  So, for an anatomist, the ear makes the whale.

  The  cavity  in  my  tympanic  bone  is  filled  with  rock,  and  that  rock

  needs to come out. In the morning, I put the bone in a little jar of weak

  acetic acid, which is similar to very strong vinegar. The acid eats the rock,

  which fizzes like soda as it dissolves, and exposes the bone. The fossil

  comes out in the late afternoon and is rinsed under running water over-

  night. Then the newly exposed bone is dried and a layer of glue applied,

  to keep the acid from eating the bone. Then the fossil is ready for its next

  acid bath. This is slow: a layer thinner than a fingernail is removed by the

  acid in each bath. But week by week, the cavity in the tympanic is emp-

  tied of rock. I watch the process under the microscope. The acid is reveal-

  ing a small lump of bone, inside the tympanic, which I assume was a

  loose bit of bone that got trapped there before fossilization. As the weeks

  wear on, the acid exposes more parts of this internal bone, revealing its

  odd shape. It is triangular, with a joint at its broadest side, and a thin

  bony bar coming off another side. The joint is not a simple round depres-

  sion, but rather two depressions joined by a low crest. This is intriguing;

  it livens up the dull acid preparation process. I perk up, and look forward

  to seeing if each acid bath will reveal more of it.

  Acid preparation is tense. Things can go wrong. If a crack in the bone

  goes unnoticed, the acid can slip behind the protective glue and crumble

  the specimen itself. Thankfully, this doesn’t happen. After innumerable acid

  baths,  eventually  the  entire  bone  is  released  from  its  forty-nine-million-

  year entombment in rock. It falls out of the tympanic shell into my palm,

  and I inspect the fossil under a microscope. I now see what it is: one of the

  three little ear bones, ossicles they are called, that transmit sound from the

  eardrum to the center of the ear. This tiny bone, the size of a grain of rice,

  has been preserved inside this ancient whale’s ear since it died (figure 3).

  Branches

  (labeled cb and cl) are intermediate

  These tiny bones transmit sound

  Pakicetus

  incus was discovered.

  Pakicetus

  All bones shown are from the left side but at different scales.

  Note how the two projections of the incus of

  Branching diagram (cladogram) that shows the relationships among whales and their relatives and the ear e 3.ru

  fig

  ossicles known for early fossil whales at the time the

  through the ear in all mammals.

  in proportions between a deer and a modern whale.

  of the diagram left unnamed will be discussed in future chapters.

  8    |    Chapter 1

  These three bones are rarely preserved in fossils because they are so

  tiny and easily lost. But they are both important and diagnostic. They

  are  called  the  hammer,  anvil,  and  stirrup  (or  the  malleus,  incus,  and

  stapes in scientific texts), and their names loosely describe their shapes in

  land  mammals.  By  vibrating,  the  bones  transmit  sound  from  the  ear-

  drum to the fluid-filled cavities near the brain, where the vibrations are

  translated into signals that are passed on to the brain. The ear ossicles of

  some marine mammals, like whales and seals, look very different from

  those of land mammals. This probably has something to do with hearing

  sounds in water, but no one knows exactly what. I realize that because

  Pakicetus was a very early whale, its ear ossicles might be important. But

  I wasn’t looking for fossil whales, and I don’t know enough about them.

  I need some bones to which I can compare my discovery.

  I read and read, and set off on a trip to the National Museum of Natu-

  ral H
istory at the Smithsonian Institution to study bones and fossils. The

  vaults behind the public exhibits there have scientific treasures—drawers

  full of fossil bones and teeth. The basement of another wing holds cabi-

  nets full of skulls and skull parts of modern cetaceans and seals. It becomes

  clear that whale ossicles are different from those of land mammals, but

  that  all  known  whales  have  similar-shaped  ear  ossicles,  including  the

  gigantic blue whale, the modest-sized porpoise, and all fossil whales.

  The  Pakicetus ossicle turns out to be an incus—the anvil. But it is

  different from the incus of a cetacean, as well as from that of a land

  mammal. The incus of land mammals has two thin bars of bone sticking

  out of it; they are called the crus breve and the crus longum.  Brevis and

  longus mean short and long in Latin, and that is indeed their relation in

  most  mammals.  But  the  relation  is  opposite  in  the  little  bone  I  have

  found in  Pakicetus.  The crus longum in this bone is fat and short com-

  pared  to  that  of  land  mammals.  Although  different  from  most  land

  mammals, the relative length of the crus longum and breve is actually

  similar to that of some even-toed ungulates, like deer and hippos. The

  position of the joints is different, too: they face differently in  Pakicetus

  than in land mammals, and are oriented in a third way in in whales.

  We write up a short paper about the bone, which makes it into the

  prestigious scientific journal,  Nature.7 Our five-day field season was not

  a complete bust after all: our wasted dig vindicated itself, although in an

  unexpected way.

  Chapter 2

  Fish, Mammal, or Dinosaur?

  the king lizard of cape cod

  Exciting though it was, that single ear bone from Pakicetus did not help

  us understand just what the earliest of whales looked like. For that, you

  need entire skeletons. And in 1992, the only ancient whale skeletons

  known were around forty million years old, compared to Pakicetus’s

  forty-nine million, and they were from other continents—Africa and

  North America. Finally, they looked quite a bit like modern whales.

  Whales, together with dolphins and porpoises, make up the Cetacea,

  and cetaceans are mammals, not fish. This was known at least as early

  as in Aristotle’s time (384–322 b.c.). He wrote, in his Historia Animal-

  ium, that whales have lungs, and that “the dolphin is viviparous, and

  accordingly, we find it furnished with two breasts, not situated high up,

  but in the vicinity of the genitals . . . and its young have to follow after

  it to suckle.”1 He also distinguished two groups of cetaceans. These are

  now called suborders: baleen whales (Mysticeti), like humpbacks, and

  toothed whales (Odontoceti), like killer whales. Toothed whales usually

  do have teeth.2 Aristotle observed that mysticetes had no teeth, but had

  “hairs that resemble hog bristles.” Mysticetes have baleen in their mouth,

  plates of a horny material used to filter food (figure 4). Aristotle’s “hog

  hairs” refer to the occasional hair on the upper lip and chin of some

  mysticetes (figure 5). Mustax in Greek means moustache, and ketos, sea

  monster, so he called mysticetes mustached sea monsters (although oth-

  ers think that Aristotle wrote mus, which means mouse or muscle).3

  9

  hairy fringe

  faces tongue

  right baleen rack

  palate

  left baleen rack

  part anchored in palate

  figure 4. Palate of a bowhead whale with baleen rack on both sides and lower

  jaws removed. Water is gulped in through the gap between the racks at the tip of the

  snout (on right of left photo) and is filtered through the baleen plates on left and

  right sides (toward top and bottom of photo), which are not connected to each other

  (as shown by Steve Ward). The hairy fringes of the plates form a matted sieve (visible

  on left rack) used to strain food out of the water. These whales have more than three

  hundred plates on each side of the jaw. This was a small, young whale. Older whales

  have longer plates (right photo, author for scale).

  figure 5. Head of a fetus of a bowhead whale showing areas that have hair (yellow

  ovals) and close-up of hair on the chin of an adult bowhead whale.

  Fish, Mammal, or Dinosaur? | 11

  So, even in the fourth century b.c., scientists knew the critical features

  that characterize a mammal: hair and nursing with milk. The great sys-

  tematist Linnaeus cemented this view in the eighteenth century. But even

  though scientists knew that whales were mammals, laymen did not. For

  many, whales’ complete adaptation to life in the water blurred their evo-

  lutionary origins. Herman Melville published Moby Dick in 1851 and

  Melville’s protagonist, the whaler Ishmael, takes on the scientists:

  In his System of Nature, A.D. 1776, Linnaeus declares, “I hereby separate

  the whales from the fish.” But of my own knowledge, I know that down to

  the year 1850, sharks and shad, alewives and herring, against Linnaeus’s express edict, were still found dividing the possession of the same sea with

  the Leviathan. The grounds upon which Linnaeus would fain have banished

  the whales from the waters, he states as follows: “On account of their warm

  bilocular heart, their lungs, their movable eyelids, their hollow ears, penem

  intrantem feminan mammam lactantes,” and finally, “ex lege naturae jure

  meritoque.” 4 I submitted all this to my friends Simeon Macey and Charley

  Coffin, of Nantucket, both messmates of mine in a certain voyage, and they

  united in the opinion that the reasons set forth were altogether insufficient.

  Charley profanely hinted that they were humbug. Be it known that, waiving

  all argument, I take the good old fashioned ground that the whale is a fish,

  and call upon holy Jonah to back me. 5

  Thus, even people intimately familiar with whales, such as the crew

  of Melville’s ship the Pequot, counted them as fish. Darwin’s Origin of

  Species was published in 1859, eight years after Moby Dick. If the place

  of whales in nature was a problem before the Origin, it got much worse

  now. Mammals, fossil and recent, lived on land. If whales are mammals,

  then their ancestors must have been land mammals. Darwin had diffi-

  culty imagining a scenario in which evolution could shape a mammal’s

  body to make it fit to return to the water. He describes one possibility in

  the first edition of the Origin:

  In North America the black bear was seen by Hearne swimming for hours

  with widely open mouth, thus catching, like a whale, insects in the water.

  Even in so extreme a case as this, if the supply of insects were constant, and

  if better adapted competitors did not already exist in the country, I can se
e

  no difficulty in a race of bears being rendered, by natural selection, more and

  more aquatic in their structure and habits, with larger and larger mouths, till

  a creature was produced as monstrous as a whale. 6

  Of course, bears do not gather food this way, but Darwin did not

  know that. The statement drew ridicule, and in subsequent editions it

  gets shorter and shorter, and eventually disappears from the Origin

  altogether. Darwin wrote in a letter to his friend James Lamont in 1861,

  12    |    Chapter 2

  “It  is  laughable  how  often  I  have  been  attacked  and  misrepresented

  about this bear.”7 Although he was convinced that whales, being mam-

  mals, had ancestors that were derived from land mammals, the fossil

  record did not preserve any intermediates. All known fossil whales were

  obligate marine mammals. In Darwin’s time, the oldest cetaceans known

  were basilosaurids—large whales with a streamlined shape easily recog-

  nizable to anyone familiar with modern whales. One hundred and thirty

  years later, when we found the  Pakicetus incus, those were still the old-

  est whales for which skeletons were known.

  But when those first basilosaurid skeletons were found, they were not

  immediately  identified  as  whales.  In  1832—before  Darwin—twenty-

  eight giant vertebrae washed out of the banks of the Ouachita River in

  Louisiana. One of the vertebrae ended up with Dr. Richard Harlan in

  Philadelphia, who published an account of the find in 1834.8 Harlan

  said that the vertebra pertained to a giant lizard. He called it  Basilosau-

  rus,  after the Greek  basileus,  king, and  saurus,  lizard. This was a mistake—making an ancient aquatic mammal sound like a terrestrial liz-

  ard—but it was an understandable one. Whale vertebrae look different

  from  those  of  land  mammals,  and  Harlan  had  only  one.  Additional

  remains of a similar beast were found in 1834 and 1835 on an Alabama