Why should anyone care about such apparently esoteric information? After all, most people can happily pass their lives without seeing a truffle of any kind, and who but an outstanding eccentric would spend hours carefully digging around in the litter under trees to find false truffles of the inedible kind? But then, who would guess that truffle evolution was crucial to the survival of several charming Australian marsupials? For the Australian group of truffles, including some placed in the genus Hydnangium, were also independently evolved in close association with Eucalyptus trees. These false truffles provide a prime foodstuff for bettongs and potoroos, which are delightful, nocturnal cat-sized animals that are now the focus of intensive conservation efforts. The more that is known of their requirements, the more likely they are to survive in the twenty-first century. False truffles are as important to their continued existence as keeping them from the depredations of feral cats. So what might at first seem extraordinarily specialized information has links to those “pretty furry things” after all; nature is seamless, its connections multifarious.
The truffle example also links back to where we started—the questions of taxonomy. Every time a truffle under examination turns out to be related to an entirely different mushroom, we can imagine a curator cursing quietly under his breath and moving the relevant preserved specimens to a different drawer. This is an extreme case of “revision”—revisiting taxonomy. The point is that we expect classification systems, genera, families and so on in ascending order, to reflect fundamental resemblances between the species included in them. The species themselves are the units of this classification—at least they are if we have recognized them correctly—and they are the real things that get shifted around from one drawer to another. The genus or family whose name might be written on the drawer or cupboard is a theoretical concept, subject to change as science advances. As with the truffles, species may be added or taken away or moved around. The up-to-date taxonomist wants his classification concepts to square with modern views. For most such scientists this means that the species included in a genus, for example, should have descended from a common ancestor—that is, constitute what is known as a clade. The characters shared by the species in a genus—and nowadays these can be molecular characters as much as the traditional “hairs on legs”—are what define it, make it a natural entity. Discover new characters and the concept of the genus may well change, and so will the species included within it. This results in changes in generic names for a given species that irritate many people, and particularly knowledgeable amateur scientists. “Why do they have to keep changing the names?” is a common complaint. However, the contemporary investigator is obliged to seek out genera, or families, that are clades; the scientific method used in recognizing these groups is known as cladistics; and the whole business of examining relationships between organisms in this way is usually termed phylogenetic analysis, or simply phylogenetics. If names have to change as a result of careful reconsideration of species, well, that’s the price of progress. Much modern taxonomy is based upon computer analysis of relationships, where all the characters possessed by a group of organisms under study are allowed to fight it out until the “best” arrangement of species is discovered, resulting in a diagram—a cladogram—showing how species relate to one another. The eventual classification is then drawn up directly from the cladogram. For example, several clades of species clustering together might be recognized as separate genera, and if these genera then cluster together in a more inclusive group this larger group might be the basis of a family.
This sounds technical, and so it is. Quite a few famous taxonomists are computer experts first, and lovers of organisms second. They think in algorithms rather than algae. They are mostly interested in animals and plants as experimental material for their classificatory computer programs. Their conversation tends to revolve around the statistical criteria for the support of one piece of the cladogram or another; an outsider hearing these people chatting might think she was overhearing an unknown Amazonian language. However, arcane though it might sound, the cladistic approach has made taxonomy much more of a science, and less dependent on the word of an authority alone. It provides a unifying method across the spectrum of organisms, from virus to vicuña, and can embrace all kinds of evidence, from the molecular to the anatomy of a blue whale. But it will be clear by now that it also makes problems for that Linnaean system of naming animals and plants. Linnaeus himself designed his “system of nature” before the notion of evolution had gained currency. Some might have considered that the order of nature might be an expression of the mind of God alone: “he made them high and lowly, he ordered their estate,” as the hymn puts it. The idea that classification might involve notions of descent from a common ancestor was a subsequent introduction. The species as the unit of currency of classification was the only thing in common between these pre-and post-Darwinian worlds. And with the arrival of cladistics and molecular analysis the old Linnaean system might be seen to creak and groan under the stress of frequent changes in nomenclature—so much so that some scientists have tried to persuade their colleagues that the time has come to abandon the Linnaean binomial altogether. They want to replace it, or at least augment it, with something called the PhyloCode.
As this is written, the PhyloCode is still undergoing its own evolution, and it might be premature to anticipate the outcome. Many critiques of the Linnaean system are surely correct. There is no consistency in the use of the ranks of the system between different kinds of organism; some parts of the natural world have small genera, other parts have large ones, and a family can be a very different concept from one worker to another. We already have an intuitive feel for this. Birds are finely divided into genera separated by tiny anatomical differences; on the other hand, some genera of plants and fungi might include several hundred species. The attractive sea snail genus Conus includes at least six hundred species. The recognition of what makes a genus or family is partly a matter of tradition and taste. It is also undoubtedly true that there are not enough categories to recognize all the different levels of relatedness that a modern cladistic “phylogenetic tree” can recognize, and nobody wants extra formal ranks with names like supersubfamilies or subsuperfamilies. There are quite enough names already.
PhyloCode is based entirely on cladistic phylogenies, and provides a system for naming clades—all of them. The old formal Linnaean categories above species level are abandoned. This is a rather revolutionary suggestion, to say the least, and it is not surprising that it has excited some strong opposition. To my mind the strict logic of the PhyloCode is beside the point. The most important thing about the current system of naming organisms is the common language it provides, not just to other systematists, but to the rest of the world—people like gardeners, or bird watchers, or fungus forayers. Very few members of this larger community know about the details of cladistic phylogenetic analysis, and I suspect that most of them want a meaningful label that they understand rather than reassurance that every category is quite the latest collection of good clades. The 250-year tradition since the great Swedish systematist does count for something. Many of the common categories that a naturalist will comfortably recognize are old Linnaean families. Think of lilies (Family Lilaceae) or daisies (Family Asteraceae) or crows (Family Corvidae). These turn out to be pretty good clades as well, meaning that the resemblance between the species in the families does indeed reflect descent from a common ancestor. In my experience more “difficult” groups of organisms are often reanalysed time and again using the latest cladistic bells and whistles or new molecular evidence, and each new analysis is rather different from the last one. Nor is there any guarantee that the latest version is always the best. Potentially all these different analyses could be named under PhyloCode. In my view this would allow for just too many valid names, as each successive analyst sought to put his imprimatur on his briefly dominant hierarchy. But most important of all is a feeling that offends my democratic instincts, in that t
he systematization of nature would be even more in the hands of a coterie of specialists sitting in front of their computers than it is now. The binomial system has faults, but I suspect any new system would develop as many. The naming process would be taken away from the naturalists, nature lovers and intelligent laymen, at a time when there has never been so much pressure on the survival of species, or, indeed, on the survival of the taxonomists who know about fleas and carabids, trilobites and ammonites, grasses and orchids, or deep-sea worms. It is the survival of the biological world and of the basis of expertise that studies it that is the real concern of the twenty-first century. Names are the least of it.
3
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Old Worlds
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It might seem an odd ambition to try to get everyone to pronounce a word correctly. But mine has always been to get the world to say “trilobite” without fudging, and with a certain measure of understanding. My own mother was wont to say “troglodyte,” which at least has a certain prehistoric dimension, even if it refers to human cave dwellers rather than extinct arthropods several hundred million years older than humans. “Did you have a nice week with the troglodytes, dear?” was one of her regular enquiries. A rather more common mispronunciation is “tribolites”—an anagram of the correct word for sure, but probably an unconscious hommage to one of the humanoid tribes on Star Trek. “The tribolites have made it through the air lock, Captain. Permission to use phasers!” I have no particular gripe against those who pronounce the word with a first syllable to rhyme with “thrill,” although I have always said “try-low-bites” myself. The tri-part, of course, refers to the threefold division into which the calcareous carapaces of these animals are usually obviously divided lengthways—“three lobes.” On their underside, but rarely preserved, were many jointed legs of typical creepy-crawly kind, which reveal the trilobites to have been distant cousins of the crabs, butterflies, spiders and millipedes, with which they should be classified—in Linnaean terms, Phylum Arthropoda, Class Trilobita. For getting on for three hundred million years trilobites swarmed in the oceans, moulting and mating, and left behind their hard carapaces in the rocks as testimony to their former importance. At the moment we know something like five thousand genera of trilobites, and new species are being discovered entombed in ancient sediments such as limestones and shales. It is not surprising that they have been described as the “beetles of the Palaeozoic.” In fact, they still have a long way to go before they approach the beetles in biodiversity, but they are wonderfully varied creatures despite their simple ground plan, some with carapaces as smooth as beans, others like arthropodan porcupines, many as large as lobsters, yet others as tiny as water fleas. They evolved fast and are not uncommon fossils, so that they are useful in dating rocks—somebody who “knows his bugs” should be able to say within a few minutes whether he is looking at Cambrian or Devonian examples; with more study the time zone can be narrowed further. Trilobites can tell about ancient climates, because different species lived in tropical as opposed to cool seas. They can tell us about vanished continents in distant eras, since different trilobites characterized different parts of the world. Study of apparently esoteric extinct animals can help us reconstruct the history of our planet.
A few years ago I wrote an account of recent discoveries of remarkable trilobites in the Devonian rocks of Morocco, dating from more than four hundred million years ago. I included an illustration of a bizarre creature that carried a trident on its head, as far as I know a unique structure in the whole animal kingdom. In 2000 this trilobite had no scientific name, although it was already possible to buy specimens of it over the internet. My colleague Pierre Morzadec named the trident-bearing genus Walliserops in 2001, commemorating a well-known Devonian specialist, Professor Otto Walliser of the University of Göttingen. In 2005 I went to Morocco to see the localities where these trilobites had been discovered. Brian Chatterton of the University of Alberta in Edmonton, Canada, has been making a study of the trilobite sites in the Anti-Atlas for several years, and he invited me to join his field party that spring. Trilobites have become a major industry in the area around the small town of Erfoud, which had previously subsisted on a little bit of tourism to add to the small rewards provided by dates and agriculture. Mr. Hammi was our guide and mentor; he is a helpful local Berber with no scientific training but a hugely intelligent “eye” for a good trilobite. Since these trilobites have to be laboriously prepared out of the rock by hand, Hammi has made a successful family business with his brother supplying splendid specimens that have finished up in collections around the world. He has partly been equipped with microscopes and tools by an English fossil dealer from Cambridge, Brian Eberhardie, who also sold on some of the best examples. I might add that there are several other successful businesses producing cheap fakes. The localities in question are dotted over one of the most barren desert regions in which I have ever worked. It seems that the High Atlas Mountains steal all the water, leaving but a trickle for the Sahara side. But the barren hillsides of the Anti-Atlas provide perfect exposure of the rock formations. This is what geologists call “layer cake” stratigraphy, where each stratum is horizontal, or gently tilted, so that climbing up a hillside from stratum to stratum is equivalent to climbing a staircase upwards through geological time. A productive layer can be traced over a long distance, or at least until a stretch of stony desert interrupts the outcrop. We went to an isolated hill called Zguilma, where trident trilobites had been collected over several years. There was actually a tree or two at the foot of the hill, tapped deep into some tiny source of water. Even in the cooler part of the year their shade was difficult to resist at three in the afternoon; in the summer it must have been impossible to work in the open.
The extraordinary sight that greeted us at Zguilma was a trilobite mine. The productive layer had been traced all along the bottom of the hillside and dug out in a series of trenches and pits, flanked by piles of debris. When Hammi arrived, muffled shouts in Arabic sounded from a hole, and out climbed a cadaverous old man with one or two yellow teeth displayed in a broad grin. He had been ten feet down in the hole in the full heat for several hours breaking hard limestone rocks. It was like being employed in Hades, with added hard labour. Mysteriously, the old man seemed cheerful enough. He was the beginning of the chain of discovery, for if he broke across one of the precious trilobites he would put both “halves” on one side, and Hammi would pay him modestly for the find. Then it would be taken on to the laboratory for preparation, and if a good trilobite were extracted, might eventually fetch up at the Houston Fossil Show or some similar event carrying a price tag of several thousand dollars. The wizened old man seemed untroubled by the chain that led to Houston, and was doubtless unaware of the profit differential; he was glad of a break to share the sweet mint tea that is the social lubricant in the desert (“Berber Whisky” is a joke for the infidel). Every evening, in the incomparably still dusk that comes in the desert, we would all share tajine made from tough old bits of meat that had spent the day hanging on string between the branches of the token tree, mopped up with Moroccan bread cooked in warm embers. We had the same bread for breakfast spread with “La vache qui rit” processed cheese. After a couple of weeks the diet began to pall. I have been allergic to laughing cows ever since.
Trilobite “mines” in the Devonian strata of the desert in the Moroccan Anti-Atlas
Several years earlier I had persuaded the Natural History Museum to purchase from Brian Eberhardie another extraordinary trilobite from Zguilma. Now I had the chance to examine where it had come from for myself: evidently, it had emerged from some hellhole. The eyes on this animal were like those of no other trilobite, because they were elevated into a pair of near vertical towers, the outer side of which were lined with very conspicuous files of lenses. Sight was obviously at a premium for this particular species. The challenge was to work out how such flamboyant “peepers” worked. One thing could not be disputed: this heavily armoured
trilobite bearing its massive eyes must have lived on the sea floor. I then noticed something curious about the eyes: they had eyeshades overhanging them. Most trilobite eyes are rather strongly curved from top to bottom, with numerous tiny lenses and no eyeshade, but this trilobite had relatively few lenses in a vertical array, so that they looked like ranks of windows in the tower. This is an appropriate simile because trilobite lenses do indeed work as a kind of window made of the mineral calcite. Because of the optical properties of this particular mineral, light passes through the lenses normal to their surface, or, to put it another way, it is possible to tell in which direction a given lens could see by imagining a ray of light impinging at right angles to its surface. So it was obvious that this remarkable trilobite could look all around over the sediment surface on which it dwelt, for the lenses were arced in a semicircle in each eye affording a “view” of the surrounding area. It obviously could not look upwards, not least because the eyeshade would inhibit the view in that direction. Then again the vertical arrangement of the lenses meant that the trilobite could see distant objects. The curved nature of most trilobite eyes means that each lens subtends a cone of sensitivity that naturally widens the farther away from the eye you are; the sight was good close by and poorer at distance. By contrast, the big-eyed trilobite with its straight-sided eye would have been able to detect small movements in prey even at some distance. But there is a problem here, for distant light is also weaker, and interference from stray rays becomes more of a problem. This is where the eyeshade comes in. For it rather neatly cuts out the light from above which affords the greatest distraction for shallow marine organisms (at moderate water depth light is refracted to come vertically from above). It is rather like a hunter on the African plains contemplating a distant impala by shading his eyes. The trilobite anticipated the baseball cap by four hundred million years.
Dry Storeroom No. 1 Page 8