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Stephen Jay Gould: Dinosaur in a Haystack

THE FASHION INDUSTRY thrives on our need to proclaim an identity from our most personal space. For
academics, who by stereotype (though not always in actuality) scorn the sartorial mode, office doors
serve the same function. Professorial entranceways are festooned with testimonies of deepest beliefs and
strongest commitments. We may, as a profession, have a deserved reputation for lengthy and tendentious
proclamation, but our office doors feature the gentler approach of humor or epigram. The staples of this
genre are cartoons (with Gary Larson as the unchallenged numero uno for scientific doors), and
quotations from gurus of the profession.
Somehow, I have never been able to put someone elses cleverness so close to my heart or soul. I wear
white T-shirts and, though I wrote the preface to one of Gary Larsons Far Side collections, I would never
identify my portal with his brilliance. But I do have a favorite quotation one worth dying for, one fit for
shouting from the housetops (if not for inscription on the doorway).
My favorite line, from Darwin of course, requires a little explication. Geology, in the late eighteenth
century, had been deluged with a rash of comprehensive, but mostly fatuous, theories of the earth
extended speculations about everything, generated largely from armchairs. When the Geological Society
of London was inaugurated in the early nineteenth century, the founding members overreacted to this
admitted blight by banning theoretical discussion from their proceedings. Geologists, they ruled, should
first establish the facts of our planets history by direct observation and then, at some future time when
the bulk of accumulated information becomes sufficiently dense, move to theories and explanations.
Darwin, who had such a keen understanding of fruitful procedure in science, knew in his guts that
theory and observation are Siamese twins, inextricably intertwined and continually interacting. One
cannot perform first, while the other waits in the wings. In mid-career, in 1861, in a letter to Henry
Fawcett, Darwin reflected on the false view of earlier geologists. In so doing, he outlined his own
conception of proper scientific procedure in the best one-liner ever penned. The last sentence is indelibly
impressed on the portal to my psyche.
and I well remember someone saying that at this rate a man might as well go into a gravelpit and
The point should be obvious. Immanuel Kant, in a famous quip, said that concepts without percepts are
empty, whereas percepts without concepts are blind. The world is so complex; why should we strive to
comprehend with only half our tools. Let our minds play with ideas; let our senses gather information;
and let the rich interaction proceed as it must (for the mind processes what the senses gather, while a
disembodied brain, devoid of all external input, would be a sorry instrument indeed).
Yet scientists have a peculiar stake in emphasizing fact over theory, percept over concept and Darwin
wrote to Fawcett to counteract this odd but effective mythology. Scientists often strive for special status
by claiming a unique form of objectivity inherent in a supposedly universal procedure called the
scientific method. We attain this objectivity by clearing the mind of all preconception and then simply
seeing, in a pure and unfettered way, what nature presents. This image may be beguiling, but the claim is
chimerical, and ultimately haughty and divisive. For the myth of pure perception raises scientists to a
pinnacle above all other struggling intellectuals, who must remain mired in constraints of culture and
But followers of the myth are ultimately hurt and limited, for the immense complexity of the world
cannot be grasped or ordered without concepts. All observation must be for or against some view if it is
to be of any service. Objectivity is not an unobtainable emptying of mind, but a willingness to abandon a
set of preferences for or against some view, as Darwin said when the world seems to work in a
contrary way.
This Darwinian theme of necessary interaction between theory and observation gains strong support
from a scientists standard take on the value of original theories. Sure, we love them for the usual big
reasons because they change our interpretation of the world, and lead us to order things differently. But

ask any practicing scientist, and you will probably get a different primary answer for we are too busy
with the details and rhythms of our daily work to think about ultimates very often. We love original
theories because they suggest new, different, and tractable ways to make observations. By posing different
questions, novel theories expand our range of daily activity. Theories impel us to seek new information
that becomes relevant only as data either for or against a hot idea. Data adjudicates theory, but theory
also drives and inspires data. Both Kant and Darwin were right.
I bring up this personal favorite among quotations because my profession of paleontology has recently
witnessed such a fine example of theory confirmed by data that no one ever thought of collecting before
the theory itself demanded such a test. (Please note the fundamental difference between demanding a test
and guaranteeing the result. The test might just as well have failed, thus dooming the theory. Good
theories invite a challenge but do not bias the outcome. In this case, the test succeeded twice, and the
theory has gained strength.) Ironically, this particular new theory would have been anathema to Darwin
himself, but such a genial and generous man would gladly, I am sure, have taken his immediate lumps in
exchange for such a fine example of his generality about theory and observation, and for the excitement
of any idea so full of juicy implications.
We have known since the dawn of modern paleontology that short stretches of geological time feature
extinctions in substantial percentages of life up to 96 percent of marine invertebrate species in the
granddaddy of all such events, the late Permian debacle, some 225 million years ago. These mass
extinctions were originally explained, in a literal and commonsense sort of way, as products of catastrophic events, and therefore truly sudden. As Darwins idea of gradualistic evolution replaced this earlier
catastrophism, paleontologists sought to mitigate the evidence of mass dying with a reading more
congenial to Darwins preference for the slow and steady. The periods of enhanced extinction were not
denied impossible in the face of such evidence but they were reinterpreted as more spread out in time
and less intense in effect, in short as intensifications of ordinary processes, rather than impositions of true
and rare catastrophes.
In his Origin of Species (1859), Darwin rejected the old notion of all the inhabitants of the earth
having been swept away at successive periods by catastrophes as well he might, given the extreme view
of total annihilation, with its anti-evolutionary implication of a new creation to start life again. But
Darwins own preferences for gradualism were equally extreme and false: We have every reason to believe
that Species and groups of species gradually disappear, one after another, first from one spot, then
from another, and finally from the world. Yet Darwin had to admit the apparent exceptions: In some
cases, however, the extermination of whole groups of beings, as of the ammonites towards the close of
the secondary period, has been wonderfully sudden.
We now come to the central irony that inspired this essay. So long as Darwins gradualistic view of mass
extinction prevailed, paleontological data, read literally, could not refute the basic premise of gradualism
the spreading out of extinctions over a good stretch of time before the boundary, rather than a sharp
concentration of disappearances right at the boundary itself. For the geological record is highly imperfect,
and only a tiny fraction of living creatures ever become fossils. As a consequence of this imperfection,
even a truly sudden and simultaneous extinction of numerous species will be recorded as a more gradual
decline in the fossil record. This claim may sound paradoxical, but consider the following argument and
Some species are very common and easily preserved as fossils; we may, on average, find specimens in
every inch of strata. But other species will be rare and poorly preserved, and we might encounter their
fossils only once every hundred feet or so. Now suppose that all these species died suddenly at the same
time, after four hundred feet of sediment had been deposited in an ocean basin. Would we expect to find
the most direct evidence for mass extinction-that is, fossils of all species through all four hundred feet of
strata right up to the very top of the sequence? Of course not.
Common species would pervade the strata, for we expect to find their fossils in every inch of sediment.
But even if rare species live right to the end, they contribute a fossil only every hundred feet or so. In
other words, a rare species may have lived through four hundred feet, but its last fossil may be entombed
one hundred feet below the upper boundary. We might then falsely assume that this rare species died out
after three fourths of the total time had elapsed.

Generalizing this argument, we may assert that the rarer the species, the more likely that its last fossil
appears in older sediments even if the species actually lived to the upper boundary. If all species died at
once, we will still find a graded and apparently gradualistic sequence of disappearances, the rare species
going first and the common forms persisting as fossils right to the upper boundary. This phenomenon a
classic example of the old principle that things are seldom what they seem and that literal appearances
often obscure reality even has a name: the Signor-Lipps effect, to honor two of my paleontological
buddies, Phil Signor and Jere Lipps, who first worked out the mathematical details of how a literal
petering out might represent a truly sudden and simultaneous disappearance.
We can now sense the power of Darwins argument about needing theories to guide observations. We
say, in our mythology, that old theories die when new observations derail them. But too often I would
say usually theories act as straitjackets to channel observations toward their support and to forestall
potentially refuting data. Such theories cannot be rejected from within, for we will not conceptualize the
disproving observations. If we accept Darwinian gradualism in mass extinction, and therefore never
realize that a graded series of fossil disappearances might, by the Signor-Lipps effect, actually represent a
sudden wipeout, how will we ever come to consider the catastrophic alternative? For we will be smugly
satisfied that we have hard data to prove gradualistic decline in species numbers.
New theories work upon this conceptual lock as Harry Houdini reacted to literal straitjackets. We
escape by importing a new theory and by making the different kinds of observations that any novel
outlook must suggest. I am not making an abstract point or waving arms for my favorite Darwinian
motto. Two lovely examples with the same message have recently been published by a pair of my closest
colleagues: studies of ammonites and dinosaurs through the last great extinction.
Anyone who keeps up with press reports on hot items in science knows that a new catastrophic theory
of mass extinction has illuminated the paleontological world (and graced the cover of Time magazine)
during the past decade. In 1979 the father-son (and physicist-geologist) team of Luis and Walter Alvarez
published, with colleagues Frank Asaro and Helen Michel, their argument and supporting data for
extraterrestrial impact of an asteroid or a comet as the cause of the Cretaceous-Tertiary extinction, the
most recent of the great mass dyings, and the time of departure for dinosaurs along with some 50 percent
of marine invertebrate species.
This proposal unleashed a furious debate that cannot be summarized in a page, much less an entire
essay, or even a book. Yet I think it fair to say that the idea of extraterrestrial impact has weathered this
storm splendidly and continually increased in strength and supporting evidence. At this point, very few
scientists deny that an impact occurred, and debate has largely shifted to whether the impact caused the
extinction in toto (or only acted as a coup de grace for a process already in the works), and whether other
mass extinctions may have a similar cause.
But paleontologists, with very few exceptions, reacted negatively at first (to say the least) and Luis
Alvarez, a virtual model for the stereotype of the self-assured physicist, was fit to be tied. (Luis, in
retrospect, was also mostly right, so I forgive his fulminations against my profession. I, if I may toot my
horn, was among his few initial supporters, but not for the right reason of better insight into the
evidence. Catastrophic extinction simply matched my idiosyncratic preference for rapidity, born of the
debate over punctuated equilibrium see essay 8.) After all, my colleagues had been supporting
Darwinian gradualism for a century, and the fossil record, read literally, seemed to indicate a petering out
of most groups before the boundary. How could an impact cause the extinction if most species were dead
But the extraterrestrial impact theory soon proved its mettle in the most sublime way of all by
Darwins criterion of provoking new observations that no one had thought of making under old views.
The theory, in short, engendered its own test and broke the straitjacket of previous certainty.
My colleagues may have disliked the Alvarez hypothesis with unconcealed vigor, but we are an
honorable lot and, as debate intensified and favorable evidence accumulated, paleontologists had to take
another look at their previous convictions. Many new kinds of observations can be made, but let us focus
on the simplest, most obvious, and most literal example. In the light of new prestige for impact and
sudden termination, the Signor-Lipps argument began to sink in, and paleontologists realized that
catastrophic wipeouts might be recorded as gradual declines in the fossil record.

How, then, to break the impasse produced by this indecisive literal appearance of petering out? Many
procedures, some rather subtle and mathematical, have been proposed and pursued, but why not start
with the most direct approach? If rare species actually lived right to the impact boundary, but have not
yet been recorded from the uppermost strata, why not look a whole lot harder? The obvious analogy to
the usual clich suggests itself. If I search for a single needle in a haystack by sampling ten handfuls of
hay, I have very little chance of locating the object. But if I take apart the stack, straw by straw, I will
recover the needle. Similarly, if I really search every inch of sediment in every known locality, I might
eventually find even the rarest species right near the boundary if it truly survived.
This all seems rather obvious. I cannot possibly argue that such an approach could not have been
conceptualized before the Alvarez hypothesis. I cannot claim that ideological blinders of gradualism made
it impossible even to imagine pulling apart the haystack rather than sampling a few handfuls. But this
example becomes so appealing precisely through its entirely pedestrian character. I could cite many fancy
cases of original theories that open entirely new worlds of observation; think of Galileos telescope and all
the impossible phenomena thus revealed. In this case, the Alvarez theory suggested little more than hard
So why wasnt the effort expended before? Paleontologists are an industrious lot; we have faults
aplenty, but laziness in the field does not lie among them. We do love to find fossils the reason why
most of us entered the profession in the first place. We didnt scrutinize every inch of sediment for the
most basic of all scientific reasons. Life is short and the world is immense; you cant spend your career on
a single cliff-face. The essence of science is intelligent sampling, not sitting in a single place and trying to
get every last one. Under Darwinian gradualism, intelligent sampling followed the usual method of
The results obtained matched the expectations of theory, and conceptual satisfaction (one might say
sloth in retrospect) set in. No impetus existed for the much more laborious technique of dismember-the-entire-haystack, a quite unusual approach in science. We could have worked by dismemberment,
but we didnt, and had no reason to do so. The Alvarez theory made this unusual approach necessary. The
new idea forced us to observe in a different way. All observation must be for or against some view if it is
to be of any service.
Consider two premier examples the best-known marine and the best-known terrestrial groups to
disappear in the Cretaceous-Tertiary extinction: ammonites and dinosaurs. Both had been prominently
cited as support for gradual extinction toward the boundary. In each case, the Alvarez hypothesis inspired
a closer look using the inch-by-inch method; and in each case this greater scrutiny yielded evidence of
persistence to the boundary, and potentially catastrophic death.
Ammonites are cephalopods (mollusks classified in the same group as squids and octopuses) with
coiled external shells closely resembling those of their nearest living relative, the chambered nautilus.
Ammonites were a prominent, often dominant, group of marine predators, and their beautiful fossil shells
have always been prized by collectors. They arose in mid-Paleozoic times and had nearly become extinct
twice before in two other mass dyings at the end of the Permian and the close of the Triassic periods. But
a lineage or two had scraped by each time. At the Cretaceous-Tertiary boundary, however, all lineages
succumbed and, to cite Wordsworth from another context, there passed away a glory from the earth.
My friend and colleague Peter Ward, paleontologist from the University of Washington, is one of the
worlds experts on ammonite extinction, and a vigorous, committed man who adores fieldwork and could
never be accused of laziness on the outcrop. Peter didnt care much for Alvarez at first, largely because his
ammonites seemed to fade out and disappear entirely some thirty feet below the boundary at his favorite
site, the cliffs of Zumaya on the Bay of Biscay in Spain. In 1983, Peter wrote an article for Scientific
American titled The extinction of the ammonites. He stated his opposition to the Alvarez theory, then
so new and controversial, at least as an explanation for the death of ammonites:
The fossil record suggests, however, that the extinction of the ammonites was a consequence not of
this catastrophe but of sweeping changes in the late Cretaceous marine ecosystem Studies of the
fossils from the stratigraphic sections at Zumaya in Spain suggest they became extinct long before
the proposed impact of the meteoritic body.
But Peter, as one of the smartest and most honorable men I know, also acknowledged the limits of such

negative evidence. A conclusion based on not finding something provides the great virtue of unambiguous potential refutation. Peter wrote: This evidence is negative and could be overturned by the finding of
a single new ammonite specimen.
Without the impact hypothesis, Peter would have had no reason to search those upper thirty feet of
section with any more care. Extinctions were supposed to be gradual, and thirty feet of missing
ammonites made perfect sense, so why look any further? But the impact hypothesis, with its clear
prediction of ammonite survival right up to the boundary itself, demanded more intense scrutiny of the
thirty-foot haystack. In 1986, Peter was still touting sequential disappearance: Ammonites appear to
have become extinct in this basin well before the K/T [Cretaceous-Tertiary] boundary, supporting a more
gradualistic view of the K/T extinctions.
But Peter and his field partners, inspired by Alvarez (if only by a hope of disproving the impact
hypothesis), worked on through the haystack: The remaining part of the Cretaceous section was well
exposed and vigorously searched and quarried. Finally, later in 1986, they found a single specimen just
three feet below the boundary. The fossil was crushed, and they couldnt tell for certain whether it was an
ammonite or a nautiloid, but this specimen did proclaim a need for even more careful search. (Since
nautiloids obviously survived the extinction the chambered nautilus still lives today a fossil nautiloid
right at the boundary would occasion no surprise.)
Peter started a much more intense search in 1987, and the ammonites began to turn up mostly lousy
specimens, and very rare, but clearly present right up to the boundary. Peter wrote in a book published in
early 1992: Finally, on a rainy day, I found a fragment of an ammonite within inches of the clay layer
marking the boundary. Slowly, over the years, several more were found in the highest levels of Cretaceous
strata at Zumaya. Ammonites appeared to have been present for Armageddon after all.
Peter then took the obvious next step: look elsewhere. Zumaya contained ammonites right to the end,
but not copiously, perhaps for reasons of local habitat rather than global abundance. Peter had looked in
sections west of Zumaya and found no latest Cretaceous ammonites (another reason for his earlier
acceptance of gradual extinction). But now he extended his fieldwork to the east, toward the border of
Spain and France. (Again, these eastern sections were known and had always been available for study, but
Peter needed the impetus of Alvarez to ask the right questions and to develop a need for making these
further observations.) Peter studied two new sections, at Hendaye on the Spanish-French border, and
right on the yuppie beaches of Biarritz in France. Here he found numerous and abundant ammonites just
below the boundary line of the great extinction. He writes in his 1992 book:
After my experience at Zumaya, where years of searching yielded only the slightest evidence near
the Cretaceous-Tertiary boundary, I was overjoyed to find a score of ammonites within the last
meter of Cretaceous rock during the first hour at Hendaye.
We professionals may care as much about ammonites, but dinosaurs fire the popular imagination. No
argument against Alvarez has therefore been more prominent, or more persuasive, than the persistent
claim by most (but not all) dinosaur specialists that the great beasts, with the possible exception of a
straggler or two, had died long before the supposed impact.
I well remember the dinosaur men advancing their supposed smoking gun of a three-meter gap the
barren strata between the last known dinosaur bone and the impact boundary. And I recall Luis Alvarez
exploding in rage, and with ample justice (for I felt a bit ashamed of my paleontological colleagues and
their very bad argument). The last bone, after all, is not the last animal, but rather a sample from which
we might be able to estimate the probable later survival of creatures not yet found as fossils. If my buddy
throws a thousand bottles overboard and I later pick up one on an island fifty miles away, I do not assume
that he only tossed a single bottle. But if I know the time of his throw and the pattern of currents, I
might be able to make a rough estimate of how many he originally dropped overboard. The chance of any
single animal becoming a fossil is surely much smaller than the probability of my finding even one bottle.
All science is intelligent inference; excessive literalism is a delusion, not a humble bowing to evidence.
Again, as with Peter Ward and the ammonites, the best empirical approach would order a stop to the
shouting and organize a massive effort to dismember the haystack by looking for dinosaur bones in every
inch of latest Cretaceous rocks. Peter means rock in Latin, so maybe men of this name are predisposed
to a paleontological career. Another Peter, my friend and colleague Peter Sheehan of the Milwaukee

Public Museum, has been guiding such a project for years. In late 1991 he published his much-awaited
Dinosaurs are almost always rarer than marine creatures, and this haystack really has to be pulled apart
fragment by fragment, and over a broad area. The National Science Foundation and other funding
agencies simply do not supply grant money at such a scale for projects that lack experimental glamour,
whatever their importance. So Peter (Sheehan this time) cleverly availed himself of a wonderful resource
that mere ammonites could never command. I will tell the story in his words:
We co-opted the longstanding volunteer-based Dig-a-Dinosaur program at the Milwaukee Public
Museum. Sixteen to twenty-five carefully trained and closely supervised volunteers and ten to
twelve staff members were present during each of seven two-week field sessions during three
summers. The primary objective of each volunteer was to search a predetermined area for all bone
visible on the surface. The volunteers were arrayed in search party fashion across exposures so
that all outcrops were surveyed systematically. Associated with the field parties were geologists
whose function was to measure stratigraphic sections and identify facies.
I cannot think of a more efficient and effective way to tackle a geological haystack. Peters personnel
logged fifteen thousand hours of fieldwork and have provided our first adequate sampling of dinosaur
fossils in uppermost Cretaceous rocks. Working in the Hell Creek Formation in Montana and North
Dakota, they studied each environment separately, with best evidence available from stream channels and
floodplains. They divided the entire section into thirds, with the upper third extending right to the impact
boundary, and asked whether a steady decline occurred through the three units, leaving an impoverished
fauna when the asteroid struck. Again, I will let their terse conclusion, summarizing so much intense
effort, speak for itself.
Because there is no significant change between the lower, middle, and upper thirds of the formation,
we reject the hypothesis that the dinosaurian part of the ecosystem was deteriorating during the
latest Cretaceous. These findings are consistent with an abrupt extinction scenario.
You can always say, So what? T. S. Eliot was wrong; some worlds at least end with a bang, not a whimper. But such a distinction makes all the difference, for bangs and whimpers have such disparate consequences. Peter Ward sets the right theme in his final statement on the non-necessary demise of
Their history was one of such uncommon and clever adaptation that they should have survived,
somewhere, at some great depth. The nautiloids did. It is my prejudice that the ammonites would
have, save for a catastrophe that changed the rules 66 million years ago. In their long history they
survived everything else the earth threw at them. Perhaps it was something from outer space, not
the earth, that finally brought them down.
The true philistine may still say, So what? If no impact had occurred, both ammonites and nautiloids
would still be alive. What do I care? I had never even heard of nautiloids before reading this essay. Think
about dinosaurs and start caring. No impact to terminate their still-vigorous diversity, and perhaps
dinosaurs survive to the present. (Why not? They had done well for more than 100 million years, and the
earth has only added another 65 million since then.) If dinosaurs survive, mammals almost surely remain
small and insignificant (as they were during the entire 100 million years of dinosaurian domination). And
if mammals stay so small, restricted, and unendowed with consciousness, then surely no humans emerge
to proclaim their indifference. Or to name their boys Peter. Or to wonder about the heavens and the
earth. Or to ponder the nature of science and the proper interaction between fact and theory. Too dumb
to try; too busy scrounging for the next meal and hiding from that nasty Velociraptor.

Stephen Jay Gould: Hooking Leviathan by Its Past

THE LANDSCAPE of every career contains a few crevasses*, and usually a more extensive valley or two for
every Ruths bat a Buckners legs; for every lopsided* victory at Agincourt, a bloodbath at Antietam.
Darwins Origin of Species contains some wonderful insights and magnificent lines, but this masterpiece
also includes a few notable clunkers*. Darwin experienced most embarrassment from the following
passage, curtailed* and largely expunged* from later editions of his book:
no difficulty in a race of bears being rendered*, by natural selection, more aquatic in their structure
Why did Darwin become so chagrined* about this passage? His hypothetical tale may be pure speculation
and conjecture, but the scenario is not entirely absurd. Darwins discomfort arose, I think, from his failure
to follow a scientific norm of a more sociocultural nature. Scientific conclusions supposedly rest upon facts
and information. Speculation is not entirely taboo, and may sometimes be necessary faute de mieux. But
when scientists propose truly novel and comprehensive* theories as Darwin tried to do in advancing
natural selection as the primary mechanism of evolution they need particularly good support, and invented hypothetical cases just dont supply sufficient confidence for crucial conclusions.
Natural selection (or the human analogue of differential breeding) clearly worked at small scale* in
the production of dog breeds and strains of wheat, for example. But could such a process account for the
transitions of greater scope* that set our concept of evolution in the fullness of time the passage of
reptilian lineages to birds and mammals; the origin of humans from an ancestral stock* of apes? For these
larger changes, Darwin could provide little direct evidence, for a set of well-known and much-lamented
reasons based on the extreme spottiness* of the fossil record.
Some splendid cases began to accumulate in years following the Origin of Species, most notably the
discovery of Archaeopteryx, an initial bird chock-full of reptilian features*, in 1861; and the first findings of
human fossils late in the nineteenth century. But Darwin had little to present in his first edition of 1859,
and he tried to fill this factual gap with hypothetical fables about swimming bears eventually turning into
whales a fancy* that yielded far more trouble in easy ridicule than aid in useful illustration. Just two years
after penning his bear-to-whale tale, Darwin lamented to a friend (letter to James Lamont, February 25,
1861), It is laughable how often I have been attacked and misrepresented about this bear.
The supposed lack of intermediary forms in the fossil record remains the fundamental canard of current
antievolutionism. Such transitional forms are sparse, to be sure, and for two sets of good reasons geological (the gappiness* of the fossil record) and biological (the episodic nature of evolutionary change, including patterns of punctuated equilibrium*, and transition within small populations of limited geographic
extent). But paleontologists have discovered several superb examples of intermediary forms and sequences,
more than enough to convince any fair-minded skeptic about the reality of lifes physical genealogy.
The first terrestrial vertebrates retained six to eight digits on each limb (more like a fish paddle than a
hand), a persistent tailfin, and a lateral-line system for sensing sound vibrations underwater. The anatomical
articulation* to hearing bones. Only one bone, called the dentary, builds the mammalian jaw, while reptiles
retain several small bones in the rear portion of the jaw. We can trace, through a lovely sequence of
ear (where they became our malleus and incus, or hammer and anvil). We have even found the transitional
form that creationists often proclaim inconceivable in theory for how can jawbones become ear bones if
intermediaries must live with an unhinged* jaw before the new joint* forms? The transitional species
maintains a double jaw joint, with both the old articulation of reptiles (quadrate to articular bones) and the
new connection of mammals (squamosal to dentary) already in place! Thus, one joint could be lost, with
passage of its bones into the ear, while the other articulation continued to guarantee a properly hinged jaw.

Still, our creationist incubi*, who would never let facts spoil* a favorite argument, refuse to yield, and
continue to assert* the absence of all transitional forms by ignoring those that have been found, and
continuing to taunt* us with admittedly frequent examples of absence. Darwins old case for the origin of
whales remains a perennial favorite, for if Darwin had to invent a fanciful swimming bear, and if paleontologists havent come to the rescue by discovering an intermediary form with functional legs and potential
motion on land, then Jonahs scourge* may gobble* up the evolutionary heathens as well. Gods taunt to
Job might be sounded again: Canst thou draw out leviathan with an hook? (The biblical Leviathan is
usually interpreted as a crocodile, but many alternate readings favor whales.)
Every creationist book on my shelf cites the actual absence and inherent inconceivability of transitional
forms between terrestrial mammals and whales. Alan Haywood, for example, writes in his Creation and
Evolution (see bibliography):
animal, which took to the sea and lost its legs A land mammal that was in process of becoming a
whale would fall between two stools it would not be fitted for life on land or at sea, and would have
no hope of survival.
Duane Gish, creationisms most ardent debater, makes the same argument in his more colorful style
(Evolution: The Challenge of the Fossil Record):
supposed land mammal ancestors It is quite entertaining, starting with cows, pigs, or buffaloes, to
The most sophisticated* (I should really say glossy*) of creationist texts, Of Pandas and People by P.
Davis, D. H. Kenyon, and C. B. Thaxton says much the same, but more in the lingo of academese:
The absence of unambiguous transitional fossils is strikingly illustrated by the fossil record of whales
If whales did have land mammal ancestors, we should expect to find some transitional fossils.
Why? Because the anatomical differences between whales and terrestrial mammals are so great that
innumerable in-between stages must have paddled and swam the ancient seas before a whale as we
know it appeared. So far these transitional forms have not been found.
Three major groups of mammals have returned to the ways of distant ancestors in their seafaring modes of
life (while smaller lineages within several other mammalian orders have become at least semi-aquatic, often
to a remarkable degree, as in river and sea otters): the suborder Pinnepedia (seals, sea lions, and walruses)
within the order Carnivora (dogs, cats, and Darwins bears among others); and two entire orders the
Sirenia (dugongs and manatees) and Cetacea (whales and dolphins). I confess that I have never quite
grasped the creationists point about inconceivability of transition for a good structural (though admittedly not a phylogenetic) series of intermediate anatomies may be extracted from these groups. Otters
have remarkable aquatic abilities, but retain fully functional limbs for land. Sea lions are clearly adapted for
water, but can still flop about on land with sufficient dexterity to negotiate* ice floes, breeding grounds,
and circus rings.
But I admit, of course, that the transition to manatees and whales represents no trivial extension, for
these fully aquatic mammals propel themselves by powerful, horizontal tail flukes and have no visible hind
limbs at all and how can a lineage both develop a flat propulsive tail from the standard mammalian length
of rope, and then forfeit* the usual equipment of back feet so completely? (Sirenians have lost every
vestige of back legs; whales often retain tiny, splintlike pelvic and leg bones, but no foot or finger bones,
embedded in musculature of the body wall, but with no visible expression in external anatomy.)
The loss of back legs, and the development of flukes, fins, and flippers by whales, therefore stands as a
classic case of a supposed cardinal problem in evolutionary theory the failure to find intermediary fossils
for major anatomical transitions, or even to imagine how such a bridging form might look or work.
Darwin acknowledged the issue by constructing a much-criticized fable about swimming bears, instead of

presenting any direct evidence at all, when he tried to conceptualize the evolution of whales. Modern
creationists continue to use this example and stress the absence of intermediary forms in this supposed
(they would say impossible) transition from land to sea.
Goethe told us to love those who yearn* for the impossible. But Pliny the Elder, before dying of
curiosity by straying too close to Mount Vesuvius at the worst of all possible moments, urged us to treat
impossibility as a relative claim: How many things, too, are looked upon as quite impossible until they
have been actually effected. Armed with such wisdom of human ages, I am absolutely delighted to report
that our usually recalcitrant fossil record has come through in exemplary fashion. During the past fifteen
years, new discoveries in Africa and Pakistan have greatly added to our paleontological knowledge of the
earliest history of whales. The embarrassment of past absence has been replaced by a bounty of new
evidence and by the sweetest series of transitional fossils an evolutionist could ever hope to find. Truly,
we have met* the enemy and he is now ours. Moreover, to add blessed insult to the creationists injury*,
these discoveries have arrived in a gradual and sequential fashion a little bit at a time, step by step, from a
tentative hint fifteen years ago to a remarkable smoking gun early in 1994. Intellectual history has matched
lifes genealogy by spanning the gaps in sequential steps. Consider the four main events in chronological
CASE ONE. Discovery of the oldest whale. Paleontologists have been fairly confident, since Leigh Van
Valens demonstration in 1966, that whales descended from mesonychids, an early group of primarily
carnivorous running mammals that spanned a great range of sizes and habits from eating fishes at river
edges to crushing bones of carrion. Whales must have evolved during the Eocene epoch, some 50 million
years ago, because Late Eocene and Oligocene rocks already contain fully marine cetaceans, well past any
point of intermediacy.
In 1983, my colleague Phil Gingerich from the University of Michigan, along with N. A. Wells, D. E.
Russell, and S. M. Ibrahim Shah, reported their discovery of the oldest whale, named Pakicetus to honor its
country of present residence, from Middle Eocene sediments some 52 million years old in Pakistan. In
terms of intermediacy, one could hardly have hoped for more from the limited material available, for* only
the skull of Pakicetus has been found. The teeth strongly resemble those of terrestrial mesonychids, as
anticipated, but the skull, in feature after feature, clearly belongs to the developing lineage of whales.
Both the anatomy of the skull, particularly in the ear region, and the inferred habitat of the animal in life,
testify to transitional status. The ears of modern whales contain modified bones and passageways that permit
directional hearing in the dense medium of water. Modern whales have also evolved enlarged sinuses that can
be filled with blood to maintain pressure during diving. The skull of Pakicetus lacks both these features, and
this first whale could neither dive deeply nor hear directionally with any efficiency in water.
In 1993, J. G. M. Thewissen and S. T. Hussain affirmed these conclusions and added more details on the
intermediacy of skull architecture in Pakicetus. Modern whales achieve much of their hearing through their
jaws, as sound vibrations pass through the jaw to a fat pad (the technical literature, for once, invents no
jargon and employs the good old English vernacular in naming this structure), and thence to the middle
ear. Terrestrial mammals, by contrast, detect most sound through the ear hole (called the external
auditory meatus, which means the same thing in more refined language). Since Pakicetus lacked the
enlarged jaw hole that holds the fat pad, this first whale probably continued to hear through the pathways
of its terrestrial ancestors. Gingerich concluded that the auditory mechanism of Pakicetus appears more
similar to that of land mammals than it is to any group of extant* marine mammals.
As for place of discovery, Gingerich and colleagues found Pakicetus in river sediments bordering an
ancient sea an ideal habitat for the first stages of such an evolutionary transition (and a good explanation
for lack of diving specializations if Pakicetus inhabited the mouths of rivers and adjacent shallow seas). My
colleagues judged Pakicetus as an amphibious stage in the gradual evolutionary transition of primitive
whales from land to sea Pakicetus was well equipped to feed on fishes in the surface waters of shallow
seas, but it lacked auditory adaptations necessary for a fully marine existence.
Verdict: In terms of intermediacy, one could hardly hope for more from the limited material of skull
bones alone. But the limit remains severe, and the results therefore inconclusive. We know nothing of the
limbs, tail, or body form of Pakicetus, and therefore cannot judge transitional status in these key features of
anyones ordinary conception of a whale.

CASE TWO. Discovery of the first complete hind limb in a fossil whale. In the most famous mistake of
early American paleontology, Thomas Jefferson, while not engaged in other pursuits usually judged
more important, misidentified the claw of a fossil ground sloth* as a lion. My prize for second worst
error must go to R. Harlan, who, in 1834, named a marine fossil vertebrate Basilosaurus in the
Transactions of the American Philosophical Society. Basilosaurus means king lizard, but Harlans
creature is an early whale. Richard Owen, Englands greatest anatomist, corrected Mr. Harlan before the
decades end, but the name sticks and must be retained by the official rules of zoological nomenclature.
(The Linnaean naming system is a device for information retrieval, not a guarantor of appropriateness.
The rules require that each species have a distinctive name, so that data can be associated unambiguously
with a stable tag. Often, and inevitably, the names originally given become literally inappropriate for the
unsurprising reason that scientists make frequent mistakes, and that new discoveries modify old
conceptions. If we had to change names every time our ideas about a species altered, taxonomy would
devolve into chaos. So Basilosaurus will always be Basilosaurus because Harlan followed the rules when
he gave the name. And we do not change ourselves to Homo horribilis after Auschwitz, or to Homo
ridiculosis after Tonya Harding but remain, however dubiously, Homo sapiens, now and into whatever
forever we allow ourselves.)
Basilosaurus, represented by two species, one from the United States and the other from Egypt, is the
standard and best-known early whale. A few fragments of pelvic and leg bones had been found before,
but not enough to know whether Basilosaurus bore working hind legs the crucial feature for our usual
concept of a satisfying intermediate form in both anatomical and functional senses.
In 1990, Phil Gingerich, B. H. Smith, and E. L. Simons reported their excavation and study of several
hundred partial skeletons of the Egyptian species Basilosaurus isis, which lived some 5 to 10 million years
after Pakicetus. In an exciting discovery, they reported the first complete hind-limb skeleton found in any
whale a lovely and elegant structure (put together from several partial specimens), including all pelvic
bones, all leg bones (femur, tibia, fibula, and even the patella, or kneecap), and nearly all foot and finger
bones, right down to the phalanges (finger bones) of the three preserved digits.
This remarkable find might seem to
clinch our proof of intermediacy, but for
one small problem. The limbs are elegant
but tiny (see the accompanying illustration),
a mere 3 percent of the animals total length.
They are anatomically complete, and they
did project from the body wall (unlike the
truly vestigial* hind limbs of modern
whales), but these miniature legs could not
have made any important contribution to
locomotion the real functional test of
intermediacy. Gingerich et al. write: Hind
limbs of Basilosaurus appear to have been
too small relative to body size to have
assisted in swimming, and they could not
possibly have supported the body on land. The authors strive bravely to invent some potential function
for these minuscule limbs, and end up speculating that they may have served as guides during copulation,
which may otherwise have been difficult in a serpentine aquatic mammal. (I regard such guesswork as
unnecessary, if not ill-conceived*. We need not justify the existence of a structure by inventing some
putative Darwinian function. All bodies contain vestigial features of little, if any, utility. Structures of lost
usefulness in genealogical transitions do not disappear in an evolutionary overnight.)
Verdict: Terrific and exciting, but no cigar, and no bag-packer for creationists. The limbs, though
complete, are too small to work as true intermediates must (if these particular limbs worked at all) that
is, for locomotion on both land and sea. I intend no criticism of Basilosaurus, but merely point out that
this creature had already crossed the bridge (while retaining a most informative remnant of the other side).
We must search for an earlier inhabitant of the bridge itself.

CASE THREE. Hind limb bones of appropriate size. Indocetus ramani is an early whale, found in shallowwater marine deposits of India and Pakistan, and intermediate in age between the Pakicetus skull and the
Basilosaurus hind legs (cases one and two above). In 1993, P. D. Gingerich, S. M. Raza, M. Arif, M. Anwar,
and X. Zhou reported the discovery of leg bones of substantial size from this species.
Gingerich and colleagues found pelvic bones and the ends of both femur and tibia, but no foot bones,
and insufficient evidence for reconstructing the full limb and its articulations. The leg bones are large and
presumably functional on both land and sea (the tibia, in particular, differs little in size and complexity
from the same bone in the related and fully terrestrial mesonychid Pachyaena ossifraga). The authors
conclude: The pelvis has a large and deep acetabulum [the socket for articulation of the femur, or thighbone], the proximal femur is robust, the tibia is long All these features, taken together, indicate that
Indocetus was probably able to support its weight on land, and it was almost certainly amphibious, as early
Eocene Pakicetus is interpreted to have been We speculate that Indocetus, like Pakicetus, entered the sea
to feed on fish, but returned to land to rest and to birth and raise its young.
Verdict: Almost there, but not quite. We need better material. All the right features are now in place
primarily leg bones of sufficient size and complexity but we need more and better-preserved fossils.
CASE FOUR. Large, complete, and functional hind legs for land and sea finding the smoking gun. The first
three cases, all discovered within ten years, surely indicate an increasingly successful paleontological
assault* upon an old and classic problem. Once you know where to look, and once high interest spurs
great attention, full satisfaction often follows in short order. I was therefore delighted to read, in the
January 4, 1994, issue of Science, an article by J. G. M. Thewissen, S. T. Hussain, and M. Arif, titled Fossil
evidence for the origin of aquatic locomotion in archaeocete whales.
In Pakistan, in sediments 120 meters above the beds that yielded Pakicetus (and therefore a bit younger
in age), Thewissen and colleagues collected a remarkable skeleton of a new whale not complete, but far
better preserved than anything previously found of this age, and with crucial parts in place to illustrate a
truly transitional status between land and sea. The chosen name, Ambulocetus natans (literally, the
swimming walking-whale) advertises the excitement of this discovery.
Ambulocetus natans weighed some 650 pounds, the size of a hefty sea lion. The preserved tail vertebra is
elongated, indicating that Ambulocetus still
retained the long, thin mammalian tail, and
had not yet transmuted this structure to a
locomotory blade (as modern whales do in
shortening the tail and evolving a prominent
horizontal fluke as the animals major means
of propulsion). Unfortunately, no pelvic
bones have been found, but most elements of
a large and powerful hind leg were recovered
including a complete femur, parts of the
tibia and fibula, an astragalus (ankle bone),
three metatarsals (foot bones), and several
phalanges (finger bones). To quote the
authors: The feet are enormous. The fourth
metatarsal, for example, is nearly six inches long, and the associated toe almost seven inches in length.
Interestingly, the last phalanx of each toe ends in a small hoof, as in terrestrial mesonychid ancestors.
Moreover, this new bounty of information allows us to infer not only the form of this transitional
whale, but also, with good confidence, an intermediary style of locomotion and mode of life (an impossibility with the first three cases, for Pakicetus is only a skull, Basilosaurus had already crossed the bridge, and
Indocetus is too fragmentary). The forelimbs were smaller than the hind, and limited in motion; these front
legs were, to quote the authors, probably used in maneuvering and steering while swimming, as in extant
cetaceans [modern whales in ordinary language], and they lacked a major propulsive force in water.
Modern whales move through the water by powerful beats of their horizontal tail flukes a motion
made possible by strong undulation of a flexible rear spinal column. Ambulocetus had not yet evolved a tail
fluke, but the spine had requisite flexibility. Thewissen et al. write: Ambulocetus swam by means of

dorsoventral [back-to-belly] undulations of its vertebral column, as evidenced by the shape of the lumbar
[lower back] vertebra. These undulations then functioned with (and powered) the paddling of Ambulocetuss large feet and these feet provided the major propulsive force for swimming. Thewissen et al.
conclude their article by writing: Like modern cetaceans, it swam by moving its spine up and down, but
like seals, the main propulsive surface was provided by its feet. As such, Ambulocetus represents a critical
intermediate between land mammals and marine cetaceans.
Ambulocetus was no ballet dancer on land, but we have no reason to judge this creature as any less
efficient than modern sea lions, which do manage*, however inelegantly. Forelimbs may have extended out
to the sides, largely for stability, with forward motion mostly supplied by extension of the back and
consequent flexing of the hind limbs again, rather like sea lions.
Verdict: Greedy paleontologists, used to working with fragments in reconstructing wholes, always want
more (some pelvic bones would be nice, for starters), but if you had given me both a blank sheet of paper and
a blank check, I could not have drawn you a theoretical intermediate any better or more convincing than
Ambulocetus. Those dogmatists who can make white black, and black white, by verbal trickery will never be
convinced by anything, but Ambulocetus is the very animal that creationists proclaimed impossible in theory.
Some discoveries in science are exciting because they revise or reverse previous expectations, others
because they affirm with elegance something well suspected, but previously undocumented. Our four-case
story, culminating in Ambulocetus, falls into this second category. This sequential discovery of pictureperfect intermediacy in the evolution of whales stands as a triumph in the history of paleontology. I cannot
imagine a better tale for popular presentation of science, or a more satisfying, and intellectually based,
political victory over lingering creationist opposition. As such, I present the story in this series of essays
with both delight and relish*.
Still, I must confess that this part of the tale does not intrigue me most as a scientist and evolutionary
biologist. I dont mean to sound jaded or dogmatic, but Ambulocetus is so close to our expectation for a
transitional form that its discovery could not provide a professional paleontologist with the greatest of all
pleasures in science surprise. As a public illustration and sociopolitical victory, transitional whales may
provide the story of the decade, but paleontologists didnt doubt their existence or feel that a central theory
would collapse if their absence continued. We love to place flesh upon our expectations (or put bones under
them, to be more precise), but this kind of delight takes second place to the intellectual jolting of surprise.
I therefore find myself far more intrigued by another aspect of Ambulocetus that has not received much
attention, either in technical or popular reports. For the anatomy of this transitional form illustrates a vital
principle in evolutionary theory one rarely discussed, or even explicitly formulated, but central to any
understanding of natures fascinating historical complexity.
In our Darwinian traditions, we focus too narrowly on the adaptive nature of organic form, and too
little on the quirks and oddities encoded into every animal by history. We are so overwhelmed as well we
should be by the intricacy of aerodynamic optimality of a birds wing, or by the uncannily precise
mimicry of a dead leaf by a butterfly. We do not ask often enough why natural selection had homed in
upon this particular optimum and not another among a set of unrealized alternatives. In other words, we
are dazzled by good design and therefore stop our inquiry too soon when we have answered, How does
this feature work so well? when we should also be asking the historians questions: Why this and not
that? or Why this over here, and that in a related creature living elsewhere?
To give the cardinal example from seagoing mammals: The two fully marine orders, Sirenia and Cetacea,
both swim by beating horizontal tail flukes up and down. Since these two orders arose separately from
terrestrial ancestors, the horizontal tail fluke evolved twice independently. Many hydrodynamic studies
have documented both the mode and the excellence of such underwater locomotion, but researchers too
often stop at an expression of engineering wonder, and do not ask the equally intriguing historians
question. Fishes swim in a truly opposite manner also by propulsion from the rear, but with vertical tail
flukes that beat from side to side (seals also hold their rear feet vertically and move them from side to side
while swimming).
Both systems work equally well; both may be optimal. But why should ancestral fishes favor one
system, and returning mammals the orthogonal alternative? We do not wish to throw up our hands, and
simply say six of one, half a dozen of the other. Either way will do, and the manner chosen by evolution

is effectively random in any individual case. Random is a deep and profound concept of great positive
utility* and value, but some vernacular meanings amount to pure cop-out*, as in this case. It may not
matter in the grand scheme of things whether optimality be achieved vertically or horizontally, but one
or the other solution occurs for a reason in any particular case. The reasons may be unique to an individual
lineage, and historically bound that is, not related to any grand concept of pattern or predictability in the
overall history of life but local reasons do exist and should be ascertainable.
This subject, when discussed at all in evolutionary theory, goes by the name of multiple adaptive
peaks. We have developed some standard examples, but few with any real documentation; most are
hypothetical, with no paleontological backup. (For example, my colleague Dick Lewontin loves to present
the following case in our joint introductory course in evolutionary biology: some rhinoceros species have
two horns, others one horn. The two alternatives may work equally well for whatever rhinos do with their
horns, and the pathway chosen may not matter. Two and one may be comparable solutions, or multiple
adaptive peaks. Lewontin then points out that a reason must exist for two or one in any case, but that the
explanation probably resides in happenstances of history, rather than in abstract predictions based on
universal optimality. So far, so good. Historys quirkiness, by populating the earth with a variety of
unpredictable but sensible and well-working anatomical designs, does constitute the main fascination of
evolution as a subject. But we can go no further with rhinos, for we have no data for understanding the
particular pathway chosen in any individual case.)
I love the story of Ambulocetus because this transitional whale has provided hard data on reasons for a
chosen pathway in one of our best examples of multiple adaptive peaks. Why did both orders of fully
marine mammals choose the solution of horizontal tail flukes? Previous discussions have made the
plausible argument that particular legacies of terrestrial mammalian ancestry established an anatomical
predisposition. In particular, many mammals (but not other terrestrial vertebrates), especially among agile
and fast-moving carnivores, run by flexing the spinal column up and down (conjure up a running tiger in
your mind, and picture the undulating back). Mammals that are not particularly comfortable in water
dogs dog-paddling, for example may keep their backs rigid and move only by flailing their legs. But semiaquatic mammals that swim for a living notably the river otter (Lutra) and the sea otter (Enhydra)
move in water by powerful vertical bending of the spinal column in the rear part of the body. This vertical
bending propels the body forward both by itself (and by driving the tail up and down), and by sweeping
the hind limbs back and forth in paddling as the body undulates.
Thus, horizontal tail flukes may evolve in fully marine mammals because inherited spinal flexibility for
movement up and down (rather than side to side) directed this pathway from a terrestrial past. This
scenario has only been a good story up to now, with limited symbolic support from living otters, but no
direct evidence at all from the ancestry of whales or sirenians. Ambulocetus provides this direct evidence in
a most elegant manner for all pieces of the puzzle lie within the recovered fossil skeleton.
We may infer from a tail vertebra that Ambulocetus retained a long and thin mammalian tail, and had not
yet evolved the horizontal fluke. We know from the spinal column that this transitional whale retained its
mammalian signature of flexibility for up and down movement and from the large hind legs that
undulation of the back must have supplied propulsion to powerful paddling feet, as in modern otters.
Thewissen and colleagues draw the proper evolutionary conclusion from these facts, thus supplying
beautiful evidence to nail down a classic case of multiple adaptive peaks with paleontological data:
Ambulocetus shows that spinal undulation evolved before the tail fluke Cetaceans have gone through a
stage that combined hindlimb paddling and spinal undulation, resembling the aquatic locomotion of fast
swimming otters. The horizontal tail fluke, in other words, evolved because whales carried their terrestrial
system of spinal motion to the water.
History channels a pathway among numerous theoretical alternatives. In his last play, Shakespeare noted
that whats past is prologue; what to come, in yours and my discharge. But present moments build no
such wall of separation between a past that molds* us and a future under our control. The hand of the past
reaches forward right through us and into an uncertain future that we cannot fully specify.

I wrote this essay in a flush of excitement during the week that Thewissen and colleagues published their
discovery of the definitive intermediate whale Ambulocetus, in January 1994. With my lead time of three
months from composition to the first publication of these essays in Natural History magazine, Hooking
Leviathan by Its Past appeared in April 1994 complete with central theme of a chronologically developing story in four stages.
I think of the old spiritual: Sometimes I get discouraged, and think my works in vain. But then the
Holy Spirit revives my soul again. Im actually a fairly cheerful soul but we all need replenishment now
and then. If there is a balm in Gilead (the songs title) for scientists, that elixir, that infusion of the holy
spirit, takes the form of new discoveries. On the very week of my essays publication, Phil Gingerich and
colleagues (see bibliography) published their description of yet another intermediate fossil whale, a fifth
tale for this gorgeous* sequence of evolutionary and paleontological affirmation. (I did feel a bit funny
about the superannuation of my essay on the day of its birth, but all exciting science must be obsolescent
from inception and I knew I could write this epilogue for my next book!)
Gingerich and colleagues discovered and named a new fossil Eocene whale from Pakistan, Rodhocetus
kasrani (Rodho for the local name of the region, kasrani for the group of Baluchi people living in the area.
Rodhocetus, estimated at some ten feet in length, lived about 46.5 million years ago. This new whale is thus
about 3 million years younger than the smoking gun Ambulocetus (Case Four and the key story in the
main essay), and about the same age as Indocetus (stage three in the main essay). No forelimb bones have
been found, and the spinal column lacks tail vertebrae, but much of the skull has been recovered with,
perhaps more important, a nearly complete vertebral column from the neck all the way back to the
beginning of the tail. Most of the pelvis has also been found and, crucial to evidence about intermediacy, a
complete femur (but no other elements of the hind limb).
We may summarize the importance of Rodhocetus, and its gratifying extension of our story about hard
evidence for intermediacy in the evolution of whales from terrestrial ancestors, by summarizing evidence
in the three great categories of paleontological data: form (anatomy), habitat (environment), and function.
FORM. I was most struck by two features of Rodhocetuss anatomy. First, the excellent preservation of
the vertebral column provides good evidence of intermediacy in a mixture of features retained from a
terrestrial past with others newly acquired for an aquatic present. The high neural spines (upward projections) of the anterior thoracic vertebrae (just behind the neck) support muscles that help to hold up the
head in terrestrial animals (not a functional necessity in the buoyancy* of marine environments, whales
evolved from a terrestrial group, the mesonychids, with particularly large heads). Direct articulation of the
pelvis with the sacrum (the adjacent region of the vertebral column) also characterizes both Rodhocetus
and terrestrial mammals (where gravity requires this extra strength), but does not occur in modern whales.
Gingerich and colleagues conclude: These are primitive characteristics of mammals that support their
weight on land, and both suggest that Rodhocetus or an immediate predecessor was still partly terrestrial.
But other features of the spinal column indicate adaptation for swimming: short cervical (neck)
vertebrae, implying rigidity for the front end of the body (good for cutting through the water as the rear
parts of the animal provide propulsion); and, especially, the seamless flexibility of posterior vertebrae
(sacral vertebrae are fused together in most large terrestrial mammals, but unfused in both modern whales
and Rodhocetus), an important configuration for providing forward thrust in swimming. Gingerich and
colleagues conclude: These are derived characteristics of later archaeocetes [ancient whales] and modern
whales associated with aquatic locomotion.
Second, and even more striking for this essays case of graded intermediacy, sequentially discovered
during the past twenty years, Rodhocetus is about 3 million years younger than the smoking gun
Ambulocetus (a marine whale with limbs large enough for movement on land as well), and a good deal older
than later whales that had already crossed the bridge to fully marine life (Basilosaurus, my Case Two, with
well-formed but tiny hind limbs that could not have functioned on land, and probably didnt do much in
water either). In the most exciting discovery of this new Case Five, the femur of Rodhocetus is about two
thirds as long as the same bone in the older Ambulocetus still functional on land (probably), but already
further reduced after 3 million additional years of evolution.

HABITAT. Rodhocetus is the oldest whale from fully and fairly deep marine waters. The oldest of all
whales, Pakicetus of Case One, lived around the mouths of rivers; Ambulocetus and Indocetus of Cases
Three and Four inhabited very shallow marine waters. Interestingly, the more fully marine habitat of
Rodhocetus correlates with greater reduction of the hind limb, for Indocetus is a contemporary of
Rodhocetus, yet grew a larger femur comparable in length with the earlier Ambulocetus. (All three creatures
had about the same body size). Thus, admittedly on limited evidence, limbs decreased in size over time and
became smaller faster in whales from more fully marine environments. (Perhaps Rodhocetus had already
ceased making excursions on land, while the earlier Ambulocetus, with a larger femur, almost surely
inhabited both land and water.) In any case, the contemporaneity of Rodhocetus (shorter femur and deeper
water) and Indocetus (longer femur with life in shallower water) illustrates the diversity that already existed
in cetacean evolution. Evolution, as I always say, no doubt to the point of readers boredom, is a copiously
branching bush, not a ladder.
FUNCTION. Rodhocetus lacks tail vertebrae, so we cant tell for sure whether or not this whale had yet
evolved a tail fluke. But evidence of the beautifully preserved spinal column particularly the unfused
sacral vertebrae, making, in the words of Gingerich et al., the lumbocaudal [back to tail] column
seamlessly flexible indicates strong dorsoventral (back to belly) flexion at the rear end of the body the
prerequisites for swimming in the style of modern whales (with propulsion provided by a horizontal tail
fluke, driven up and down by bending the vertebral column). I was particularly pleased by this result, since
I closed my essay with a mini-disquisition on multiple adaptive peaks and the importance of historical
legacies, as illustrated by vertical tail fins in fishes vs. horizontal flukes in whales both solutions working
equally well, but with whales limited to this less familiar alternative because they evolved from terrestrial
ancestors with backs that flexed dorsoventrally in running. Gingerich and colleagues conclude: This
indicates that the characteristic cetacean mode of swimming by dorsoventral oscillation of a heavily
muscled tail evolved within the first three million years or so of the appearance of the archaeocetes.
A tangential comment in closing: The sociology of science includes much that I do not like, but let us
praise what we do well. Science at its best is happily and vigorously international (see essay 20) and I can
only take great pleasure in the following list of authors for research done in an American lab based on
fieldwork in Asia, supported by the Geological Survey of Pakistan: Philip D. Gingerich, S. Mahmood Raza,
Muhammad Arif, Mohammad Anwar, and Xiaoyuan Zhou. Bravo to you all. I also couldnt help noting the
papers first sentence: The early evolution of whales is illustrated by partial skulls and skeletons of five
archaeocetes of Ypresian (Early Eocene) age. The geological time scale is just as international, for our
fossil record is a global scheme for correlating the ages of rocks. So a layer of sediments in Pakistan may be
identified as representing a time named for a place that later became the bloodiest European battle site of
World War I the dreaded Ypres (or Wipers as British soldiers named and pronounced their hecatomb).
But so much for lugubrious* and sentimental thoughts. Lets just end in the main essays format for our
new case of Rodhocetus:
CASE FIVE. Open and shut.
Verdict: sustained in spades*, wine and roses.

aquatic, adj /@"kw&tIk/

articulation, n a joint or connection that permits
assault, n a violent attack
assert, v /@"s3;t/ to state sth clearly and forcefully
as the truth
buoyant, adj /"bOI@nt/ that can float or continue
to float
chagrin, n /"S&grIn/ a feeling of disappointment
or annoyance at having failed, made a mistake etc.
comparable, adj /"kQmp@r@bl/
comprehensive, adj that includes everything or
nearly everything
cop out, v to avoid or ewith draw from doing sth
one ought to do, because of being afraid, lazy, etc.
crevass, n /kr@"v&s/ a deep open crack, esp. in ice
curtail, v /k3;"teIl/ to make sth shorter or less
expunge, v /Ik"spVndZ/ to remove words or
names complete from a list, book, etc.
extant, adj still in existence
feature, n a distinctive characteristic; an aspect
for only da nur
forfeit, v /"fO;fIt/ to give up sth
gap, n an empty interval of space or time
glossy, adj 1 smooth and shiny 2 making a show
of being smart and expensive but of little real
worth or importance
gobble up, v to eat sth fast, and in a greedy and
sometimes noisy way
gorgeous, adj /"gO;dZ@s/ wonderful
ill-conceived, adj fr schlechten Stil; fr
injury: add insult /"InsVlt/ to injury to make
ones relationship with sb even worse by offending them as well as actually harming them
joint, n a structure in the body by which bones
are fitted together and are able to move or bend

lopsided, adj /%lQp"saIdId/ not evenly balanced

lugubrious, adj sad; full of sorrow
manage, v to succeed in doing sth
marine, adj /m@"ri;n/
meet, v to play, fight, etc. together as opponents
in a contest
mo(u)ld, v /m@Uld/ to shape or influence sb/sth
negotiate, v /nI"g@USieIt/ to get over or past an
obstacle etc. successfully
nomenclature, n /n@U"menkl@tS@/
punctuated equilibrium die Theorie, da Phasen
der (fast vollkommenen) Stabilitt von (kurzen)
Zeiten starker Vernderung unterbrochen werden
relish, n great enjoyment, pleasure, or satisfaction
render, v to cause sb/sth to be in a specified
scale, n the relative size, extent, etc. of sth
scope, n the range or extent of matters being dealt
with, studied, etc.
scourge, n /sk3:dZ/ a person or thing that causes
trouble or suffering
sloth Faultier
sophisticated, adj /s@"fIstIkeItId/ complicated and
refined; elaborate; subtle
in spades to a high degree, with great force
spoil, v to ruin sth
spotty, adj not even (in quality)
stock, n a persons family or ancestors
taunt, v /tO;nt/ to try to make sb angry or upset by
saying insulting things to them or by mocking them
unhinged, adj /Vn"hIndZd/ ausgeklinkt
utility, n the quality of being useful
vestigial, adj /ve"stIdZi@l/ remaining as a vestige
/"vestIdZ/ [a small remaining part of what once
yearn, v /j3;n/ to desire sth strongly and with
great emotion

Phonetische Symbole



Vowels and diphthongs