THE SIGNIFICANCE OF LITTLE THINGS
We seem important to ourselves because of our intimate knowledge of mankind, derived from the evidence of our senses. Niagara and the Grand Canyon seem huge to us. Yet the telescope reveals among the stars wonders of such magnitude that, in comparison, our earth dwindles to an insignificant speck and the human beings upon it shrink to the dimensions of microscopic germs. . . . Therefore, size is relatively unimportant. The most significant factor is life, which is of the same nature in microscopic organisms as in ourselves.
—Curator of Living Invertebrates Roy W. Miner, as
quoted by D. R. Barton in “A Modern Gulliver,”
in Natural History, November 1941.
From the earliest days of the Museum’s history, its scientists have been entranced by some of the most fascinating yet little-understood members of the great panoply of life on earth: Invertebrates, creatures with no backbones ranging from protozoa to beetles to snails. Invertebrates can teach us perhaps the most important lessons of all about evolution and biodiversity.
Why evolution? Because such extinct invertebrates as ammonites and trilobites lived and evolved for such a long time—scores of millions of years—and left such an extraordinary fossil record. “It’s impossible to study ancient invertebrates,” says Niles Eldredge, a curator in the Division of Paleontology and an expert in trilobites and evolution, “and not be interested in the ways species evolve.”
Why biodiversity? Because there are hundreds of times more invertebrate species—including insects and spiders—living today than the combined total of all vertebrate species. Because every entomologist on earth could spend the rest of his or her life describing new invertebrate species, barely take time to eat and sleep, and have no chance to keep up with the flood of new species to discover. (For more on past and current research on insects and spiders, see Chapter 5, “Tiny Glories of Biodiversity.”)
You can learn a lot about evolution by studying ancient mammals. You can study biodiversity by cataloging the birds of the tropical rain forest. But for insights into these fascinating, critically important subjects that you simply can’t find elsewhere, you must understand the significance of little things.
Invertebrate specimens were among the first to join the collection at the nascent American Museum. In fact, it was an important collection of fossil invertebrates that helped bring the Museum to the brink of bankruptcy during its shaky first years—while simultaneously leading to the hiring of its first high-profile curator.
In 1874, before the first building was even open, the museum spent $65,000 for a huge trove of fossil invertebrates owned by Professor James Hall, official New York State geologist. This collection was one of the finest in the world, comprising more than seven thousand species, and the Museum trustees who had okayed the purchase thought it was exactly the kind of acquisition to help bring the new Museum the respect it needed.
The Museum did gain respect in the scientific community, but made an almost fatal miscalculation in expecting any great enthusiasm among nonscientists. As Douglas Preston puts it in Dinosaurs in the Attic, his 1986 history of the Museum, “The Museum hoped to pay for the Hall Collection with a public subscription. Unfortunately, the public proved to be quite uninterested in an aggregation of gray invertebrate fossils. Very little money came forth.”
As a result, the Museum’s trustees had to pay for the collection out of their own pockets—an onerous commitment that led them to forbid most other expensive purchases. As a result, when the Museum’s first building opened in 1877, the few visitors who ventured to this northwest frontier of Manhattan found the exhibition halls to be virtually empty. “By 1880, the Museum was on the brink of extinction,” Preston writes. “Museum President Robert L. Stuart had said that when he retired, he would recommend closing the Museum if no one could be found to take his place.”
The man the trustees found to replace Stuart in 1881 was Morris K. Jesup, who transformed the Museum exhibition areas, its collections, and its mission. Jesup realized immediately that the public was far more likely to be interested in large, spectacular creatures like lions than in fossil invertebrates. As far as fossils went, it was fine for the curators to collect these small specimens, but couldn’t they bring in some dinosaur fossils as well? Perhaps even some entire dinosaur skeletons to fill the empty exhibition halls?
By the time Jesup arrived and changed the Museum’s course, the administration (led by Theodore Roosevelt) had already hired a specialist to oversee the benighted Hall Collection: Robert Parr Whitfield (1828–1910), an associate of Professor Hall’s and a vitally important participant in the building of a successful museum.
Whitfield, nearing fifty by the time he came to the Museum, grew up in Oneida County, New York, a region then famous for its abundant fossils. Like Barnum Brown, George Gaylord Simpson, and many other budding paleontologists, he spent his youth collecting and studying fossils, but unlike these men, Whitfield never had the benefit of university training in his field. “At the age of nine, the boy [Whitfield] began work in a cotton mill, later entering the shop of his father, who was a spindle maker,” wrote geologist E. O. Hovey. “School education did not fall to his lot; in fact . . . his entire school training amounted to less than three months of time in all, and he never saw the inside of a school house as a student after he was twelve years old.”
Whitfield played an important role in the development of research at the Museum. He also had strong ideas about departmental organization, as he showed in an 1890 letter to President Jesup objecting to the naming of a separate curator to lead each department. “The result of such a course is most generally that each head of a department will have their own views in regard to arrangements,” he complained. “The fewer heads there are, the better the results.”
At least during his lifetime, Whitfield’s views held sway, as can be seen in this litany of staff positions he occupied during his three decades at the Museum:
1877–1884 |
Curator of Geology |
1885–1886 |
Curator of Geological and Mineralogical Department |
1887–1890 |
Curator of Geological, Mineralogical, and Conchological Departments |
1891–1900 |
Curator of the Departments of Geology, Mineralogy, Conchology and Marine Invertebrate Zoology |
Curator of Department of Geology and Invertebrate Paleontology |
The fluid nature of departmental categories reveals much about the youth of both the Museum and the natural sciences it was studying. Research into invertebrates, in particular, seemed to have trouble finding a home, and through the years both the objects on display and the scientists studying the important collection have been moved frequently.
Once the Museum’s finances were restored to order and more popular displays were installed in the new building’s vast showcases, R. P. Whitfield was able to study and display the vast Hall Collection without worrying whether it would support the entire Museum. “The Hall Collection of fossils was his idol,” wrote Hovey, “and its care and interests were constantly on his mind.” This intense focus on the Museum’s fossil invertebrate collections as a whole allowed Whitfield to produce many important scientific works, including an enormous catalogue of the Museum’s more than eight thousand type specimens, published in 1898. (Type specimens are those from which a new, previously unknown, species is identified.)
One of Whitfield’s greatest accomplishments was to establish a regular forum for the Museum’s scientists to publish their research findings. At Whitfield’s urging, President Jesup funded a new journal, the Bulletin of the American Museum of Natural History, beginning in 1881. Whitfield wrote the first five articles for the new journal and contributed many other articles until 1910, the last year of his life. Today, the Bulletin continues to be one of the leading journals of scientific research in the world, regularly publishing the findings of Museum invertebrate biologists Neil Landman, Niles Eldredge, Norman Newell, Judith Winston, and others—as well as the findings of scientists from every other biological department in the Museum.
For decades during the first half of this century, Museum scientists and preparators engaged in an ambitious effort to spur public interest in some of the smallest of all invertebrate animals: the microscopic, single-celled organisms known as protozoa, which include amoebas, paramecia, and countless others known only to scientists.
As early as 1909, Roy W. Miner was employing his colorful writing style to describe these minute organisms in a lead Journal article. “Swarming in countless millions in both fresh and salt water, and at times even in the bodies of other animals, they are the most abundant and widely distributed of all life,” Miner wrote. “Though this vast world of creatures is so important and surrounds us on every side, penetrating, as it were, all the interspaces between the larger forms of life, yet it is invisible to our eyes, and were it not for the compound microscope, we should be absolutely ignorant of it, except in its effects.”
In his writing, Miner could have made laundry interesting—but he would never have succeeded in capturing Museum visitors’ attention if not for the brilliant artistry of preparator Herman O. Mueller, descendant of a long line of German glass-blowers and the man responsible for some of the most beautiful objects on display in the Museum.
Along with making the glass coral polyps for the coral reef group, Mueller labored for years to create a series of glass models of protozoa. Working with almost incomprehensible delicacy, utilizing tiny particles of various types of glass to produce subtle changes in color and texture, he was able to reproduce the most delicate cell walls, filaments, and other structures that make protozoa as diverse and mysterious as snowflakes. Today, the results of Mueller’s decades of labor still provide an unparalleled look at these little-known microorganisms.
THE COMPLICATED LIFE OF SMALL ANIMALS
Have you ever met a crab walking along a path and wondered how the crab has managed to survive so far from the sea, since crabs always live in sea water—or do they? . . . For all that shrimps, lobsters and crabs are familiar animals, how much do you know about them as moving, feeding, breathing, reproducing organisms—living organisms?
—Invertebrates Curator Dorothy Bliss,
in Shrimps, Lobsters and Crabs (1982).
Invertebrate animals occupy nearly every environment on earth. They thrive in temperate and tropical forests, inhabit frigid mountaintops, make up the vast preponderance of undersea life, even survive on the Arctic tundra and Antarctic ice cap. Where life is found on the planet, invertebrates are certain to be there.
So it should be no surprise that invertebrates can be found in many of the Museum’s halls. Mollusks and their long relationship with human cultures are featured in the Mollusks and Our World hall. Ammonites occupy their own showcase, as do a giant millipede and other magnified invertebrate dwellers of the forest floor. But one fascinating exhibit—showing a Caribbean coral reef and its inhabitants—can easily be overlooked, as it resides in the dramatic Hall of Ocean Life, and tends to be overshadowed by the gigantic blue-whale model hanging overhead and the dioramas featuring leaping dolphins, hulking walruses, and other more spectacular creatures.
The Caribbean exhibit shouldn’t be missed, because it involves one of the world’s most ancient, complex, and fascinating ecosystems. Coral polyps are tiny invertebrate animals, each of which secretes a rocklike skeleton around itself. In uncountable numbers, colonies of polyps form coral reefs, extraordinarily rich ecosystems that can harbor dozens of species of fish and many other marine animals.
The diorama is also notable because so much effort took place in constructing an accurate replica of a living reef. Only a few times in Museum history has a curator striven as hard and for as long as did Curator of Living Invertebrates Roy Waldo Miner in seeking to transplant a coral reef into a New York City building.
Miner and a covey of assistants, including several preparators, modelmakers, and artists, made five separate trips to the Caribbean over a span of twelve years, beginning in 1923. During the initial expedition to the reefs of Andros Island in the Bahamas, the explorers had access to an amazing “submarine tube,” which was exactly what it sounds like: A long tube extending down thirty feet from a specially designed barge and culminating in a spherical viewing chamber much like a bathysphere.
In these days of scuba, research submersibles, and robot subs that can explore the undersea world thousands of feet beneath the surface, it’s hard to remember a time when glimpses of even the shallow-water reef environment were a rare and precious gift. But in 1923 the diving tube, which allowed a comfortable descent to about thirty feet, granted almost unprecedented access, as Miner pointed out in an enthusiastic article he penned in 1924 for a newspaper called Mid-Week Pictorial.
“Our first glimpse through the window of the submarine tube revealed a sight so marvelous as to be almost startling in its strange beauty,” Miner wrote. “A dense forest of palmate corals, like stone trees with interlacing branches, of which the uppermost pierced the water surface, rose from the reef platform and melted into the pearly blue of the watery fog, while beams from the afternoon sun penetrated between their fronds and illuminated numerous schools of fish which passed in solemn review before us, lighting up their brilliant color patterns like gleaming jewels.”
After recovering from their first view of a “fantastic world belonging to a strange planet,” Miner and his assistants spent hours every day sketching, photographing, and filming the reef and its inhabitants. Then, on this and succeeding trips, they utilized early diving helmets to descend and collect among the coral heads. Remarkably, a Museum artist named Chris Olsen actually painted reef scenes while seated twenty feet beneath the ocean surface, equipped with waterproof paints and canvas, weighted brushes, and, of course, a diving helmet.
But the hardest job was yet to come: reconstructing the beauty, complexity, and fragility of the reef ecosystem in a habitat group. Merely cleaning the forty tons of delicate, often branching coral required six months of hard work, and mending broken branches and fans took weeks more. Each specimen was then coated with beeswax “to simulate the animal layer, which in life invests the coral,” as Miner put it, and artists carefully painted the faded specimens with oil paints to recapture their natural colors. Before the great coral heads could be placed in the diorama, ironworkers designed and erected a frame capable of supporting the massive specimens while remaining invisible.
The background and smaller reef inhabitants also received careful attention. Modeler Chris Olsen created a great limestone cavern backdrop; glassblower Herman Mueller modeled glass replicas of living coral polyps; preparators made wax models of hundreds of reef fish; and artist Francis Lee Jaques painted the glowing background.
The resulting habitat group, which finally went on display in 1935, portrays a dimly lit scene that comes close to capturing the beauty and mystery of a real reef—close enough, at least, that it should inspire generations of young Museum visitors to visit the real thing. As Miner wrote in a statement of philosophy shared by the Museum’s scientists and preparators today, “The ideal museum group is not merely a work of art. It is a record of living beings in their natural state and environment, depicted in their proper relations to their surroundings, and emphasizing the truth that the real unit in nature is the association rather than the individual.”
Miner wasn’t the only Museum specialist in invertebrates to study coral reefs. But Curator Emeritus Norman Newell, who has been associated with the Museum for more than fifty years, has chosen a far more rigorous route. He has tackled a variety of fascinating questions surrounding ancient and modern reefs, the use of the fossil record to study evolution, and—pivotally—the mass extinction of much of the world’s marine life that occurred during a period around the time of the end of the Permian and beginning of the Triassic period, about 248 million years ago.
In 1995, Newell and Museum research associate William Boyd (emeritus professor at the University of Wyoming) published a Bulletin article, “Pectinoid Bivalves of the Permian-Triassic Crisis,” the last in an important series of ten papers on the extinct members of a group of bivalves known as pectinoids. (Bivalves are animals with two-valved shells, such as clams.) By studying populations of these bivalves on either side of the line separating the Permian from the Triassic periods, the authors were seeking further insights into what might have caused the mass extinction of that time.
Newell and Boyd’s research, while not firmly supporting a single hypothesis, shows that diversity of pectinoid bivalves declined from about twenty-three genera in the middle Permian to just five in the late Triassic, and didn’t begin to recover until millions of years later. “So they shared the great mass extinction with most other groups of marine invertebrates,” the authors conclude. “The crisis extended some tens of millions of years and was slow, rather than catastrophic.”
The authors don’t subscribe to a single theory as to what caused the mass extinction. As they say at the conclusion of the article, “The search for some general explanation of the Permo-Triassic mass extinction is still in full swing, with many, by no means mutually exclusive, viable hypotheses.” These hypotheses, they go on to explain, include lowering of sea levels, flooding of continents with oxygen-poor water from the deep sea, changes in salinity, strong volcanic eruptions, sudden climatic changes, gamma-ray bursts from super novas, and a collision between the earth and a large comet or asteroid.
Scientists may never learn exactly why the earth’s oceans went through a period of such dramatically depressed productivity during the Permian-Triassic crisis. It is likely that a combination of the factors listed above contributed to the extinction—and also quite possible that other factors, as yet undiscovered, also played a major role.
Newell and Boyd feel that their most important discovery—detecting a downward trend in the ratio of certain carbon isotopes that parallels the progressive extinction of bivalve species to the Permian-Triassic boundary—may provide important new directions for research. Rather than depending on fossil evidence alone, they say, scientists should combine geochemical and fossil evidence to learn what happened to the pectinoid bivalves and so many other marine invertebrates at this time.
Like Norman Newell, other department curators have studied both living and extinct invertebrate species. Curator Emeritus William K. Emerson, for example, has written prolifically on fossil mollusks from Baja California and other locations, while also researching the distribution of living mollusks in the tropical eastern Pacific Ocean. This important work, focusing on Clipperton, Cocos, and the Revillagigedo and Galapagos Islands, is providing insights into both the evolutionary history of the region’s mollusks and the islands’ biogeography as isolated outposts of land within the eastern Pacific’s major oceanic current systems.
Newell’s research on living mollusks builds off one of the most extensive collections in the Museum. In 1874, just five years after its founding, Catherine Wolfe (daughter of John David Wolfe, the Museum’s first president) purchased the Jay Collection and gave it to the Museum. This collection included fifty thousand specimens of fourteen thousand mollusk species, and was just the first of many large collections that came to the Museum in the years that followed. Today, the Museum harbors a stunning 275,000 catalogued lots of living and fossil invertebrates, an irreplaceable resource for scientists worldwide.
Not all invertebrate specialists studying living species have focused on mollusks. Libbie Hyman and Dorothy Bliss both turned their attention elsewhere, but could not have been more different in the approaches they took to research.
Libbie Hyman (1888–1969) never wanted to study a single species or even group of invertebrates. Instead she chose to look to broader horizons. Her chief enthusiasm, she wrote, was for nature in general. “This first took the form of a love of flowers,” she said, adding, “I believe my interest in nature is primarily aesthetic.”
She also always claimed to have little interest in basic research. “I do not regard any of this work as of outstanding importance,” she said of some of her early studies at the University of Chicago. “I am not a research type.” According to former Museum invertebrates curator Judith Winston, however, Hyman was being too modest. As Winston pointed out in a newsletter published by The American Society of Zoologists, Hyman “published more experimental papers than many scientists ever do.”
Still, since Hyman didn’t see herself as being cut out for research or (as she also claimed) for teaching, what was her role to be after her arrival at the Museum in 1937? Her decision was to take on the immense task of producing The Invertebrates, the first work to compile and organize all known information about the vast number of creatures without backbones.
Hyman worked on the treatise for more than thirty years, and eventually produced six large volumes. For this accomplishment above all she was awarded the Daniel Giraud Elliot Medal of the National Academy of Sciences and the Linnean Gold Medal of the Linnean Society of London—in both cases, she was the first woman zoologist ever to receive the medal.
“Her books provided a synthesis of phylogeny that clearly influenced teaching and opinion about the groups she covered,” Judith Winston wrote in 1991. “While discoveries of the last 30 years have resulted in many changes in our thinking about invertebrate phylogeny, her work still provides a framework against which new ideas can be tested and sets a standard of excellence that can still inspire us.”
While Libbie Hyman’s love was for nature in general, Dorothy Bliss chose a far more intense focus for her research. Bliss (1916–1988) was a neuroendocrinologist who studied the effects of hormones on the nervous system. As a curator and eventual chairwoman of what was then called the Department of Living Invertebrates, she focused almost all of her life’s work on hormones in crustaceans, particularly in a single species of tropical land crab named Gecarcinus lateralis.
Between 1956 and her death, Bliss studied how hormones influence the crab’s ability to molt, to maintain a water balance in its body (a particularly important factor for a land crab), and to move. Among her findings were that captive crabs molted only when temperature, moisture, and illumination matched those found at the end of the crab’s burrow. In improper conditions, molting was delayed by release of previously unknown “molt-inhibiting factors” from cells located in the crab’s eyestalks.
The lifelong intensity of Bliss’s desire to learn about the innermost workings of crabs remains striking today. In Shrimp, Lobsters and Crabs, an in-depth popular book she wrote in 1982, she gave a hint as to why she pursued the path she did, writing that “there is a fascination about shrimps, lobsters, and crabs, their structure, their behavior, the lives that they live.” Throughout her life and through her work, Dorothy Bliss helped us share her enthusiasm for these often little-noticed creatures.
AMMONITES AND MASS EXTINCTION
I enjoy studying ammonites because they can tell us so much about evolution in the Mesozoic Era. Why? Because there were so many of them and they were so widespread. You can call the Mesozoic the Age of Dinosaurs—but to me it was just as much the Age of Ammonites. And that means you can track their history through both time and space.
—Neil Landman, Curator in the Division of Paleontology.
The study of ammonites—shelled extinct relatives of the modern-day nautilus, octopus, and squid has a long but sporadic history at the American Museum. After R. P. Whitfield’s death in 1910, responsibility for the collection was assumed by the Department of Geology, under the leadership of curators more interested in earth science than paleontology. Similarly, when most Museum fossil hunters went into the field, they were looking to make the next great dinosaur or mammal find—rarely taking the time to excavate small, seemingly unspectacular invertebrate specimens.
Luckily for the Museum’s collection, there were exceptions to this pattern. During a 1918–1919 expedition to Cuba, Vertebrate Paleontology’s Barnum Brown collected a large number of ammonites from the Jurassic period, excavating in seven different sites that covered 15 million years of Jurassic exposures. Soon after his return, invertebrate paleontologist Marjorie O’Connell undertook the first truly systematic and paleogeographic analysis of ammonites ever made at the Museum.
As reported in a 1921 issue of the in-house Museum newsletter, Museologist, O’Connell’s goals were similar to those of scientists studying extinct animals today. “Biologically the specimens are interesting because they throw new light on the broader problems of organic evolution and the laws which control it,” the newsletter explained. “Geologically the collection is valuable because it marks the only occurrence of rocks of Jurassic age in the West Indies and makes possible the establishment of a geological column of rock formations which can be compared with those of Mexico and Europe.”
When O’Connell and Brown combined the paleontological and geological data, they found that they were able to draw a far more accurate map than any before of the extent of the Jurassic oceans. The widespread ammonites allowed them to conclude that the oceans of the time stretched from Mexico to cover much of what is now Europe, inundating most Mediterranean countries and parts of Russia, Germany, France, and England.
The Museum’s next important ammonite collection was excavated by mammalogist Herbert Lang during the Museum’s Vernay Angola Expedition of 1925. Perhaps because he was no paleontologist and the chief goal of this expedition was the collecting of mammals and birds, Lang got the material to the Museum in good shape but with little supporting information. Then it had to wait until 1940 for a qualified invertebrate paleontologist, Curator Otto Haas, to study it. Haas produced a two-hundred-page Bulletin article that still stands as a model of careful description and analysis.
If ammonites received only occasional attention during the Museum’s first century, that is clearly no longer the case. Pay a visit to the large, sunlit office of Curator Neil Landman, and you’ll step into a room that fulfills the dream of any child who’s ever wondered what a fossil-hunter’s office looks like. Every surface seems to be covered in ammonites: Tiny specimens whose delicately whorled shells seem as fragile as flowers; larger ones burnished red, brown, even golden, depending on the color of the sediment in which they were preserved; ammonites lining the tops of tables, arranged so every few inches represent a million years of evolution.
Landman himself takes evident pleasure in being surrounded by these fascinating remnants of ancient times. During a conversation, he wanders around the room, stopping frequently to pick up one or another ammonite to demonstrate a point he is making. “One of the things that makes studying ammonites so satisfying is how much information is packed into their shells,” he says, cradling a specimen whose shell has been laid open to reveal its spiral chambers. “Since every ammonite adds new chambers as it grows, each one contains a complete record of its life history.”
Remarkably, this record includes the ammonite’s embryonic growth, the first delicate chambers created while it was still in the egg. “Every so often we find an exceptional specimen with no matrix—no rock—adhering to the shell, and we can use a scanning electron microscope to study the smallest details of the chambers,” Landman says. “To have such a complete record means that we have many characters to compare systematically, including shell shape, the design of the septa [the partitions between chambers], and other features that allow us to put together ammonite genealogies.”
Though his office seems to contain enough specimens to occupy a scientist for years, Landman has long realized that productive systematic work depends on a steady influx of new specimens. Therefore, each year he collects specimens in Montana, South Dakota, and Wyoming, which were all part of a vast Cretaceous seaway that stretched from the Arctic to the Gulf of Mexico and from the Rocky Mountains at least to Kansas. Since some of this sea’s ammonite species have also been found in Greenland and Poland, it seems that this seaway must have connected in some way with oceans covering what are today parts of Europe and Greenland.
Just as Barnum Brown’s Cuban ammonites allowed him and Marjorie O’Connell to delineate the borders of a Jurassic ocean, Landman’s specimens enable him to practice the science of paleobiogeography in the Cretaceous. “Since ammonites were active swimmers, and many species were widely distributed, they give us an opportunity to understand where the seas were,” he explains. “These intercontinental correlations, as we call them, give us crucial data about life in ancient times.”
While careful, rewarding systematic work and paleobiogeography are both central aspects of Landman’s research, he (along with other ammonite specialists) finds himself drawn to one of the most fascinating questions surrounding these cephalopods: Why did every last ammonite become extinct at the end of the Cretaceous period?
The mass extinction at the end of the Cretaceous is by far the most famous cataclysm in earth’s history. This was the extinction event, apparently spurred in part by some enormous collision between the earth and a giant comet or asteroid, that claimed the great dinosaurs, all pterosaurs, ichthyosaurs, and plesiosaurs, and countless smaller creatures. So it shouldn’t be surprising that ammonites disappeared as well.
But what bothers scientists is another question: Why did ammonites become extinct while their relatives, the nautilids, survived? (Today, 65 million years after the last ammonite, nautilids still live in the South Pacific and Indian Oceans.) A glance at the Late Cretaceous data makes it seem as if the situation should have been reversed.
After all, as Landman points out, in the last part of the Cretaceous (called the “Maastrichtian”), ammonites were far more diverse than the nautilids, with about twenty-one genera compared to a mere seven nautilid genera. In sheer abundance they were equally dominant: At least one estimate put the number of individual ammonites in South Dakota rock strata in the hundreds of millions, compared to fewer than ten thousand nautilids.
So what happened? “We’ll never know for sure, so any hypotheses are speculation,” Landman warns. “But I believe that their ultimate extinction—and the nautilids’ survival—may have been due to differences in their early development.”
When living nautilids hatch, they are already quite large and able to swim actively. Almost immediately after hatching, they descend to just above the sea bottom at depths of about one thousand feet (their preferred habitat). Once there, they act as scavengers, showing little preference for specific foods. Analysis of fossil nautilids indicate they may well have followed a similar lifestyle.
“Ammonites, on the other hand, were tiny—about half a millimeter—at hatching,” Landman says. “It seems that they spent the early portion of their life as plankton, swimming near the surface of the ocean.”
Surface waters are far more sensitive to environmental changes than are deeper waters. Changes in ocean currents, oxygen levels, or chemistry would therefore leave the inhabitants of surface water—such as the ammonites and other planktonic animals—uniquely vulnerable to extinction. And, in fact, a large portion of planktonic animals died out at the end of the Cretaceous. The free-swimming adult ammonites might have been able to survive the drastic environmental changes of the time, but their young could not.
“It’s strange,” Landman says, gazing down at the fossils that are all that remain of this once-dominant group of marine animals. “Looking at ammonites during the late Cretaceous, you would have thought that they’d go on forever. It just goes to show how unpredictable the history of life is.”
The most dramatic exhibit in the Museum’s Hall of Ocean Life features the great blue whale, the largest animal ever to live on earth. But the spookiest display in the same hall features a different kind of whale, the sperm whale, grappling with another giant creature. This creature, the giant squid, remains one of the most mysterious and elusive of all large animals.
The giant squid is a monster-sized, deep-sea version of the familiar squids that populate shallower waters. Scientists know that giant squids can reach sixty feet in length and weigh in at a thousand pounds. Large individuals can have eyes as big as soccer balls, although no one knows what purpose these eyes serve in the squid’s pitch-dark haunts nearly a half mile below the ocean’s surface.
In a way, it’s remarkable that scientists know so much about the giant squid, because no one has ever seen one of these magnificent animals alive. Everything we know comes from dead specimens caught in the fishermen’s nets—and even from sucker marks left by squids’ tentacles on sperm whales, which scientists think hunt and eat the squids.
Now, for the first time, visitors to the Museum will have the chance to get an up close look at an actual giant squid, though not a living one. Late in 1997, a New Zealand fishing boat pulled up a dead but intact twenty-five-foot-long squid in its nets. The squid was promptly placed in the boat’s freezer, where it remained until the boat returned to shore. There it was turned over to local scientists, who eventually decided to donate it to the Museum.
The squid cleared customs at New York’s Kennedy Airport by being stamped “seafood.” Once at the Museum, though, it wasn’t destined to become calamari but rather to be studied by Neil Landman and other invertebrate specialists. From there it traveled one last short hop to its final destination, a huge tank in the Hall of Biodiversity. Here it provides Museum visitors with a striking example of the diversity of the Earth’s living creatures, and of how much we still have to learn about the animals that inhabit the last frontiers of our planet.
PUNCTUATED EQUILIBRIUM: BURSTS OF EVOLUTION
The norm for a species or by extension, a community is stability. Speciation is a rare and difficult event that punctuates a system in homeostatic equilibrium. That so uncommon an event should have produced such a wondrous array of living and fossil forms can only give strength to an old idea: paleontology deals with a phenomenon that belongs to it alone among the evolutionary sciences and that enlightens all its conclusions—time.
—Stephen Jay Gould and Niles Eldredge, announcing
their theory of punctuated equilibrium in Models in
Paleobiology (T.J. M. Schopf, editor), 1972.
Paleontology curator Niles Eldredge studies the long-extinct arthropods called trilobites (those ancient relatives of crabs, lobsters, and pill bugs), but a few minutes of conversation or a glance at his list of published works makes it clear that he has another passion: sharing the fascinating “inside story” of modern science with the world outside the scientific establishment. Among the stories he has to tell is one that turns on its head everything most of us thought we knew about evolution.
In 1972, Eldredge and Stephen Jay Gould, professor of geology at Harvard University and Frederick P. Rose Honorary Curator in Invertebrates at the Museum, developed the theory they called “punctuated equilibrium”—or, as Eldredge casually refers to it, “punc eq” (pronounced “punk eek”). This theory states that Charles Darwin was wrong in some of the crucial details of his revolutionary theories of evolution.
Darwin believed that constant environmental pressures—the endless battles of natural selection, resulting in the survival of the fittest—caused steady, gradual, and virtually constant evolution in every species. Punc eq states that this is not true; instead, evolution of species into new forms takes place in dramatic bursts separated by huge time spans in which virtually no evolution takes place at all.
“As a neonate in 1972, punctuated equilibrium entered the world in unusual guise,” wrote Eldredge and Gould in a 1993 article in Nature. “We claimed no new discovery, but only a novel interpretation for the oldest and most robust of palaeontological observations: the geologically instantaneous origination and subsequent stability (often for millions of years) of palaeontological ‘morphospecies.’ ” That is, among extinct animals, the fossil record has always demonstrated long periods of stasis punctuated by evolutionary bursts that “instantly” (in geologic time) creates new species.
“Rather than accept the fossil evidence showing that one of Darwin’s central tenets needed adjusting, paleontologists claimed that the record itself was flawed,” Eldredge explains. “No one can argue that there are notorious holes in the fossil record, but all of the evidence points to punctuated equilibrium as the mode of evolution.”
In a Natural History article cowritten by Niles and Michelle J. Eldredge in 1972 (the year the theory was announced), the authors used a trilobite (Phacops rana) that inhabited the Devonian seas of North America to demonstrate how the fossil record supports the idea of evolutionary bursts. “P. rana had a very large compound eye on each side of the swollen, rounded middle region of the head, prompting the name rana, which means frog,” the Eldredges wrote. “Each eye is covered with many lenses arranged in vertical rows around the eye. Twice in the long evolutionary history of this trilobite, the number of vertical rows of lenses was reduced, giving rise to a new variety of P. rana each time.”
Extensive research, which involved hunting for P. rana specimens from New York to Michigan, showed that the transition from eighteen rows of lenses to seventeen and then to fifteen took place in two brief bursts. In both instances, the transition occurred in nearshore environments of the eastern Devonian sea, at times when the sea shrank in size on its western edge. Each time, the more primitive form of P. rana (the one with greater numbers of lenses) disappeared, replaced when the seas returned by the new variety that had evolved in the east. Except for these dramatic events, the trilobite existed unchanged (once with eighteen rows, once with seventeen) for as long as 8 million years.
“Perhaps the most amazing feature of the entire Phacops rana story is its stasis—a persistence against change—through vast amounts of time,” the authors concluded. “Contrary to popular belief, evolutionary change seems to occur infrequently, and usually in small, isolated populations in a short span of time. The bulk of species’ history is stasis, and there is no inexorable, progressive evolutionary march through time.”
As might be expected, such pronouncements raised a storm of controversy. Amid what Gould and Eldredge call “an astonishing lack of evidence” for Darwin’s gradualistic theories, other paleontologists severely criticized punc eq’s reading of the fossil record. So did evolutionary biologists studying living species, despite the fact that evidence seemed to indicate a punctuated course of evolution and speciation among living creatures as well.
As the authors point out, the theories developed by the brilliant evolutionist Ernst Mayr (an ornithologist at the Museum for many years) show that speciation tends to occur in small populations isolated from the parental stock, not in a steady course in large, central populations. This mode of speciation, they add, “would yield stasis and punctuation when properly scaled into the vastness of geologic time,” much as it did with P. rana, in which the new form, having evolved in isolation, swept across the Devonian sea after a period of environmental upheaval.
Gould, Eldredge, and many other scientists (notably Steven M. Stanley and Elisabeth S. Vrba) have refined the theory of punctuated equilibrium since 1972. Early on, Gould and Eldredge focused on the tempo of the evolutionary bursts, seeking to delineate patterns over time. Today, more research focuses on the causes of stasis and evolution, as well as on creating a new definition of “macroevolution,” an overview of evolutionary trends among all species over time.
In the quarter of a century since the theory was unveiled, it has gradually become more widely accepted in the scientific establishment. Ernst Mayr, who had criticized the theory, relented somewhat in the face of overwhelming evidence. “I agree with Gould that the frequency of stasis in fossil species revealed by the recent analysis was unexpected by most evolutionary biologists,” he acknowledged in his 1992 book The Dynamics of Evolution. “It’s not that everyone agrees with us, but at least they are willing to discuss it,” Eldredge comments.
Recently, researchers have discovered evidence of punctuated equilibrium in the evolution of mollusks, mammals, and other groups. And, in a fascinating series of laboratory experiments reported in 1996, a team of Michigan State University scientists found that bacteria tended to evolve to greater size over time, but that this evolution took place in sudden bursts after thousands of generations with no observed change. In other words, punctuated equilibrium.
Despite such encouraging support for their theory, Gould and Eldredge are taking the long view as to whether they’ve uncovered the true design of the evolution of life. This is how they conclude their 1993 update in Nature: “Thus, in developing punctuated equilibrium, we have either been toadies and panderers to fashion, and therefore destined for history’s ashheap, or we had a spark of insight about nature’s constitution. Only the punctuational and unpredictable future can tell.”