Leonardo’s Mountain of Clams and the Diet of Worms
Page 18
The Camel’s hump is an ugly lump
Which well you may see at the Zoo;
But uglier yet is the hump we get
from having too little to do.
I think that we owe nature a favor in return to expiate this exploitation of a long-standing evolutionary product, developed without the slightest human influence, and presumably long before our origin. So I too have a tale of a hump to tell—but for a different animal and an opposite purpose. In Kipling’s version, the camel develops a hump in order to serve a human master diligently. In the story of this essay, we discover the existence of a hump only because ancient humans painted pictures of a feature that no conventional evidence of the fossil record could ever have revealed. I hope that nature will accept this trade: we rip off a well-known hump to construct a moral fable of dubious merit (Kipling’s camel), but our ancestors restore another by providing the only possible evidence for a hump that would otherwise have disappeared into the maw of lost history (the Irish Elk of this essay).
We know that certain mammals, from camels to Quasimodo, have humps. Deer, however, do not grow humps—although large deer with big antlers (moose, in particular) often develop a broadly raised area on their backs, in the shoulder region where forelegs meet backbone. But the deer with the largest antlers of all time, the extinct (and misnamed) Irish Elk, did evolve a prominent hump—a wonderful fact that we can only know because human artists painted these giant deer on cave walls. A hump, as fatty tissue, does not fossilize.
Megaloceros giganteus, the so-called Irish Elk, surely heads the hit parade of extinct deer. In a famous quip, Voltaire remarked that the Holy Roman Empire had been misnamed in all attributes—for this amalgam of largely Germanic lands in central Europe was neither holy, Roman, nor an empire. Similarly, the Irish Elk was neither exclusively Irish nor an elk. This species lived in temperate climates throughout Europe and western Asia (with close relatives in Siberia and China), from about 400,000 years ago to a last record in Ireland at 10,600 years B.P. (before the present). The Irish epithet derives from the superb preservation and frequent occurrence of Irish specimens, buried (and hermetically sealed) in sediments beneath layers of peat in the island’s numerous bogs. A cottage industry developed in the nineteenth century for excavating and selling specimens to museums and collectors throughout the world—hence the identification with Ireland. (A 1994 article by Adrian M. Lister provides a summary of virtually all science and lore about Irish Elks. I have also studied this species extensively, and have published both technical accounts—see my 1974 article cited in the bibliography—and general articles, including the very first essay that I ever wrote in this series, now spanning eight volumes and more than 250 essays.)
The “elk” misnomer has a more complex history. Early scientists thought that the Irish fossils might represent the same species as the American moose, then poorly known. Moose, in Europe, are called elk—hence the confusion. In any case, since Megaloceros is not a moose, the common name makes no sense. In this essay, I shall follow the practice of all current experts on these fossils, and refer to Megaloceros as the “giant deer.”
Giant deer had large bodies, about equal in size to those of modern moose, although slightly exceeded by a fossil deer species or two. But the antlers of Megaloceros—the source of celebrity for the genus—hold all records for size and weight. Growing outward from the head, essentially at right angles to the body axis, these large palmated antlers (platelike rather than sticklike) could reach a span of up to thirteen feet from tip to tip, and a weight of one hundred pounds. When we recognize that male giant deer shed and regrew these structures annually (females grew no antlers), our wonder at the energetic drain can only increase.
In the light of this essay’s focus on earliest human interactions with giant deer, I note that the history of scientific discussion about Megaloceros has always centered on questions of potential human contact with such a bizarre and fascinating creature. Two issues dominated the early literature.
1. IS THE GIANT DEER, OR ANY SPECIES, FOR THAT MATTER, TRULY EXTINCT? In the eighteenth century, as the Linnaean approach to classification became codified, and as the nascent science of geology began to reveal the earth’s great age, a major debate arose among European naturalists: Could an entire species become extinct? Many leading naturalists rejected the possibility, either on traditional creationist grounds (for a hole would then be left in a system of relationships ordained as permanent and complete by an omniscient God), or by arguments derived from early forms of evolutionary thought (in Lamarck’s system, for example, species maintained too much adaptive flexibility to die, though they could transform to higher states).
But if species couldn’t die, where was the animal that, in ages past, left such magnificent antlers under the Irish peat bogs? Some scientists believed that the uncharted forests of Canada might still house the giant deer, perhaps in the degenerated form of the smaller-antlered American moose. (As mentioned previously, this conjecture led to the false name of “Irish Elk” for the giant deer.)
This debate ramified into a set of interesting byways. On the political front, a full-time statesman and sometime paleontologist named Thomas Jefferson blasted the great French naturalist Georges Buffon for his claim that all American species must be smaller and degenerated versions of European forms (including the American moose as a demoted giant deer). As his touché, Jefferson wrote a paper on the fossil claw of a giant lion, surely larger than any Old World counterpart. Unfortunately, the claw actually belonged to a large ground sloth—showing once again that neither patriotism nor morality should be staked upon the uncertain facts of nature.
On the artistic front, Britain’s finest painter of animals, George Stubbs, did a portrait of the Duke of Richmond’s yearling bull moose, the first to enter Britain. This work, executed in 1770, depicts the young moose on a mountain ledge, with storm clouds gathering in the background, and a pair of adult antlers lying in the foreground. The painting has long been celebrated, but the circumstances of composition have only recently come to light. The work was commissioned by the great Scottish medical anatomist William Hunter as part of a project (never published) to determine whether or not the American moose might represent the same species as the fossil Irish giant deer—hence Stubbs’s depiction of adult antlers in the foreground! (See W. D. Ian Rolfe’s 1983 article, cited in the bibliography.)
Proponents for extinction slowly gained the upper hand as further exploration, including the expedition of Lewis and Clark, encountered no living Megaloceros—while moose dropped from the running as their differences from giant deer become more apparent. Georges Cuvier, Europe’s premier anatomist and founder of modern vertebrate paleontology, provided a final resolution in 1812, when he published his four volume Recherches sur les ossemens fossiles (Researches on Fossil Bones) and proved both the fact of extinction in general, and the death of the giant deer in particular. Speaking with customary force, Cuvier wrote of the giant deer:
Here is the most famous of all fossil ruminants, the one that naturalists regard, with greatest unanimity, as lost from the earth . . . It is certain that the Irish antlers could not belong either to the moose or the reindeer . . . This [fossil] species could not possibly be confused with any large [modern] deer on any continent.
2. DID HUMANS EVER INTERACT WITH GIANT DEER? Once the fact of extinction had been settled, scientists turned their attention to the timing and manner of dying. Proponents of human interaction with giant deer suffered a major setback in the key Irish localities, for humans did not reach the Emerald Isle (or at least did not leave any known bones or artifacts to indicate their presence) until well, after the demise of Megaloceros. What, then, of the giant deer’s large European range? Our Neanderthal cousins and, later, our Cro-Magnon ancestors certainly overlapped the giant deer in time, but did humans ever interact with Megaloceros, or did we share territory in mutual ignorance, like Longfellow’s ships passing in the night?
Giant deer a
re never common in continental European fossil beds. From this and other evidence, paleontologists infer that the species always lived at low population density, and would probably have been noted by humans only as a minor element in any local fauna. Some giant deer bones had been found in apparent conjunction with human artifacts, but evidence remained inconclusive because the most undeniable criterion—representation of the species in Paleolithic art—had long yielded nothing positive. In a key article published in 1949, G. F. Mitchell and H. M. Parkes wrote: “It may perhaps be pointed out again that there are no representations of the Giant Deer in Paleolithic cave art.”
Science tends to be difficult, subtle, ambiguous, and biased by all manner of social and psychic prejudice—though surely directed in a general way toward increasingly better understanding of a real world “out there.” But every once in a while, we do achieve the reward of a simple, pristine, and undeniable fact—and then we can simply rejoice. In 1952, the first clear Megaloceros appeared on a newly discovered cave wall—a gift from our ancestors, and a positive solution to the question of whether humans ever interacted with giant deer. The cave of Cougnac, in south-central France, yielded three paintings of Megaloceros, two males and a female. Deer can be difficult to distinguish in cave art, for the paintings are partly symbolic and not entirely representational, and some species of deer differ only subtly. But the antlers of Megaloceros are so distinctive, and the second male of Cougnac so clearly painted, that the attribution could scarcely be doubted. Few deer have palmated, or platelike, antlers. The fallow deer, Dama dama, presents the only real possibility of confusion with Megaloceros—but the tines (points) of fallow deer spring from the posterior border of the palm, while giant deer tines project from the front edge. The Cougnac painting clearly depicts a large palmated antler, with tines springing from the anterior border.
One is a great discovery, but generalities require at least two. Forty-five years after the opening of Cougnac, giant deer remain rare in cave art—thus supporting my earlier inference that Megaloceros remained an uncommon animal in ice-age Europe. Only four sites have been identified, and only one other locality satisfactorily affirms the Cougnac discovery. The cave of Peche Merle, known before Cougnac, contains a schematic figure of a probable giant deer—really little more than a rough finger sketch in clay. The antler does emit a strong whiff of Megaloceros, but I wouldn’t put much money on this figure—and no one did before Cougnac confirmed the presence of giant deer in cave art. The recently discovered cave of Cosquer also contains two probable giant deer, but the identification requires comparison with Cougnac—and the Cosquer images alone could not have made a convincing case for Megaloceros in Paleolithic painting.
Thus, only one other find truly ranks as an independent affirmation of Cougnac, and as proof that our ancestors interacted with giant deer. The recently discovered cave of Chauvet (see the previous essay) contains two beautifully rendered giant deer. Neither painting includes the distinctive antlers, but all other defining features, as known from fossil bones and the Cougnac paintings, have been faithfully depicted, and the identification seems firm. (Both deer have been interpreted as females, and probably correctly so, but I wonder if one or both might not be males with shed antlers, for a small projection next to the ears could represent pedicels—the projecting bases of shed antlers, found only in males. In any case, the depiction of one sex alone makes sense in natural history, though such a decision may, of course, only reflect the symbolic purposes of the artists. In two excellent articles in the 1980s, paleontologist Anthony Barnosky proved from Irish localities that males and females lived in separate herds for part of the year—as many species of deer do today.)
For paleontologists, cave art provides precious evidence far beyond a mere proof of interaction with ancient humans. Consider the chief frustration of the conventional fossil record: that we must rely upon the evidence of bones and other preservable hard parts. So much that is so vital for any understanding—shapes of soft parts, colors, sounds, behaviors—simply do not fossilize. Our science depends crucially on modes of inference (often dubious or even fanciful) from a paltry preserved record to the richness of nature’s totality. Sometimes we can draw a reasonable conclusion: When we find a shark’s tooth embedded in an ammonite’s shell, we know something about the diet of ancient fishes. But often we just can’t tell: I cannot, for example, even imagine how we might learn crucial details about the emergence of human language, since so many millennia passed between original invention and the codification of any written system that might be preserved in the geological record. (In this context, I confess to wry amusement, bordering on annoyance, at the success of “dinomation” exhibits in museums—robotic dinosaurs that gyrate and howl. Public fascination for these models centers upon the very features—colors, sounds, and soft body flaps and frills—that must remain entirely conjectural.)
Paleontologists therefore treasure the rare geological circumstances that permit an occasional preservation of soft parts. Much of our most crucial knowledge about life’s history requires these precious “windows” upon the complete anatomy of ancient creatures. We would never have known the full range of the Cambrian explosion if the Burgess Shale had not preserved soft parts as well as shells—for many of these earliest animals grew no hard parts at all. We would never have identified Archaeopteryx as the first bird if the lithographic limestone of Solnhofen did not preserve feathers as well as bones.
All these “windows” exist as a result of rare geological conditions, usually involving rapid burial in fine-grained sediments lacking both oxygen and a bacterial biota poised to decompose anything soft and organic. (Entombment in amber produces the same effect.) Only one new mode has been added by life’s own complexity—unfortunately rather late in time, and quite limited in range. Human artists rendered the soft parts (and sometimes even the colors) of the fauna of ice-age Europe—and we, their descendants, are forever in their debt for this unique style of window into the past.
Even without a boost from cave art, we can learn more about ice-age mammals than about most other creatures of a more distant past—for complete and well-preserved skeletons can often be found, and the animals tend to be familiar as a consequence of their close affinity with living species. But many important features must still remain obscure when bones provide our only evidence. For example, we can infer the existence of an elephant’s or tapir’s trunk from the distinctive form of nasal bones, but we cannot learn much about size, color, or function. Similarly, fossil camels are almost always drawn without humps—not because we have any reason to assert their absence, but because we cannot infer their probable presence from bones alone.
Consider the most pressing question that bones alone cannot resolve about the form of giant deer. Our interest in this species has always focused—quite understandably, given their outlandish size—upon the antlers. How could an animal with a five-pound skull grow up to one hundred pounds of antlers year after year? Any structure of such size and exaggeration must require a substantial set of compensatory adaptations in other bodily parts—and much of the scientific discussion about giant deer has centered upon the redesign of the rest of the body to support the gigantic antlers. Adrian Lister argues, for example, that the remarkably thickened lower jaw bones may act as a source of recruitable storage—as they do to a lesser extent in some modern species of deer—for calcium that can be transferred to the antlers. Valerius Geist has shown that such enormous antlers impose severe constraints upon forage, for only a few plant species can supply enough minerals in the time required. Geist inferred that only willows could suffice, and he then discovered willow remains stuck in the teeth of giant deer fossils!
But most compensatory adaptations perform the more basic function of supporting the antlers in a biomechanical sense. For example, the top of the skull is unusually thick, and the first few vertebrae of the neck remarkably powerful and especially wide (as needed for the insertion of large muscles and ligaments that suppo
rt the head). Most remarkably, as shown in the figure drawn by the great British anatomist Richard Owen (see page 191), the spines of the first few dorsal vertebrae (in the shoulder region) project far up from the backbone. In his History of British Fossil Mammals and Birds, published in 1846, Owen first noted the existence and significance of these projections as compensatory adaptations for the enormous antlers:
The dorsal vertebrae are thirteen in number, and the anterior ones are remarkable for the length of the spinous processes which give attachment to the elastic ligaments supporting the head: those of the third, fourth, and fifth dorsals rise to a foot in height.
Modern studies have affirmed Owen’s insight about the crucial status of spines on the dorsal vertebrae. A key structure, appropriately named the ligamentum nuchae (or neck ligament), supports the neck in modern deer (and other mammals) by attaching both to the occiput (back) of the skull and the first few cervical (neck) vertebrae in the head region, and then extending back to an insertion on the spines of the dorsal vertebrae in the shoulder region. The stronger the neck vertebrae, and the longer the spines of the dorsal vertebrae, the more powerful the ligament—all the better to hold up the massive head. All these structures, unsurprisingly, grow especially large in giant deer! (On the form and function of the ligamentum nuchae, see the 1985 article, listed in the bibliography, by N. J. Dimery, R. McN. Alexander, and K. A. Deyst.)
The long dorsal spines of giant deer imply some expression in the shape of the body—but of what form, and to what significance for the animal’s function and behavior? Other large deer and related animals also possess elongated dorsal spines, and a broadly raised area around the shoulder region as a consequence—as in modern moose or bison.