The image of the modern laboratory is one of humming machines counting atoms of oxygen isotopes while a scientific technician in a white coat wearing thick glasses and thin gloves stares at a computer console. In my experience this image is almost entirely correct. Hence I am grateful for the existence of the laboratory, or, as I now have to call it, the Conservation Unit, in the Palaeontology Department. It still has fossil bones and microscopes and interesting things on benches. People still get their hands dirty with ordinary dirt. Much of its business these days is preparing casts—including some famous hominid specimens—which can be made with an accuracy and stained to resemble the original in a way that Charles Dawson would surely have admired. Here the “BM Archaeopteryx” is copied for other museums around the world, prepared in a light resin that imitates the original in a way far more delicate than the old plaster-of-Paris casts. The laboratory is in the basement of the building, so that large lumps of rock can be admitted directly through the double doors at the back. From time to time something so important is discovered that everybody drops everything to get it in through those doors. The discovery of the dinosaur Baryonyx was one such occasion. Mr. Walker found the claw of Baryonyx in 1983 in a quarry in Cretaceous rocks at Otley in the English Weald. From a subsequent visit to the site by Museum scientists, it became clear that much of the skeleton was preserved in sandstone blocks in the quarry; furthermore, it seemed to be an altogether new kind of dinosaur. This kind of excitement is rare. All the available staff took off to Otley to collect as much as possible, carefully recording the relative position of bones and making plaster cradles for more fragile specimens. When the dinosaur was eventually brought in through the back doors, it was the job of master preparator Ron Croucher to extract it from the rock. This was a task somewhat similar in magnitude to carving the faces of those presidents of the United States of America on Mount Rushmore, except that close-up details matter rather more, and it was a question of extracting reality from the rock rather than sculpting the rock to a known design.
Ron Croucher is a most self-effacing kind of man, but I believe he has little doubt that Baryonyx walkeri is his masterpiece. His apprenticeship as a preparator went back to the early days of the Palaeontology Department. In the old Museum the “lab” was housed in dreadful conditions at the north side of the building. It was so cold in winter that a series of electric fires were propped all over the place to keep the staff warm, and the lighting was so poor that it was sometimes necessary to wait for the sun to creep into the room before a particularly delicate task could be undertaken. Nonetheless, innovative work was carried out there. The staff pioneered the use of resins in casting fossils, which is now routine. On one occasion in the old hierarchical days, a very senior scientist and mollusc specialist, Dr. L. R. Cox, appeared in the laboratory at teatime in search of milk; apparently, his tea club of senior chaps had run out of it. A beaker of the latest resin lay on the bench, opaque and white. Without a by-your-leave, Dr. Cox appropriated the liquor and swept out. The subsequent reaction in the senior tea club is not recorded. Ron Croucher’s predecessor, Arthur Rixon, pioneered the extraction of fishes from limestone by acid solution. A fish—like us—has bones of calcium phosphate, whereas limestone is calcium carbonate; the latter dissolves in certain acids, acetic acid perhaps being most commonly employed, leaving the bones untouched. The result can be the most exquisite preparations of fossils, as precise as a dissection, with no tool brought to bear on the fragile skeleton.
No such short cuts were possible in the case of Baryonyx. Ron had to cut off the sandstone surrounding the bones grain by grain using a vibrating air pen with a hardened tip. It is painstaking work: a moment’s lapse in concentration can polish off the work of days. In the case of Baryonyx, extraction was even more difficult, because the bones were softer than the surrounding rock. Certainly much more than a year of Ron’s life went into the work; he says that he lost all sense of time after a while. The final result is a reconstruction of the dinosaur as a specialized fish eater, a predator with an almost crocodile-like skull and huge claws; it is related to Spinosaurus, but tells a new story about the adaptability of the ruling reptiles to different life habits. Ron’s contribution was acknowledged in the scientific description of Baryonyx by Alan Charig and Angela Milner—a formal nod towards his hours and hours of patient toil. When dinosaurs appear in books and films as realistic as if they had been plucked from the Cretaceous by a time machine, it is easy to forget that everything we know is the result of the labours of unsung masters like Ron Croucher. Reality is extracted out of sight of the public in back rooms full of half-exposed bones.
Preparing a mounted skeleton of the dinosaur Baryonyx in the “laboratory”
Some people think of huge dinosaurs as more or less synonymous with fossils. At the other extreme are the molecules making up the genes that have controlled the course of evolution from microbe to mankind. It might be thought that fossils and genes would never meet, but recent research has made it happen. Palaeobotanists study the fossils of plants. More primitive plants have survived to the present day than animals, so you can find flourishing examples of Ginkgo trees, cycads or monkey puzzle trees that would not have been out of place when Baryonyx walked abroad in the Weald. There have been a number of palaeobotanists associated with the Natural History Museum, not all of them happy appointments, although the collections are as vast as you might expect. K. I. M. Chesters, who was palaeobotanist when I joined the Museum, seemed rather uninterested in fossil plants, which is not a good qualification for the job, although she had produced some publications in the 1950s: she had a large loom in her office, and I believe she was weaving when she should have been working. When she married another member of the department, the “alga man” Graham Elliott, wags suggested he had been bribed by the Keeper to do the right thing for the department. She left shortly afterwards.
The present incumbent, Paul Kenrick, is a humorous and dynamic man in his forties who is concerned particularly with the early history of land plants, and knows a lot about those ancient groups, like ferns and horsetails, that have survived from what is often referred to as “deep time.” Fossils provide a direct way of learning about early plants and their relationships. Another route is to study the genomes of the survivors from former times. Similarities and differences in their gene sequence patterns reveal their degrees of relatedness—at least, if the right “designer gene” can be identified, as I described in the last chapter. This method has led to the recognition of evolutionary branching events that happened tens or even hundreds of millions of years ago. It may also suggest in turn where a particular fossil may fit on the evolutionary tree, thus allowing cross-fertilization between palaeontology and molecular biology. As a high point of this method, a remarkable, sequence-based evolutionary tree for all the flowering plants was produced in 1993, something that botanists had desired, but failed, to do since Darwin’s time. Since the early seed-bearing plants were contemporaries of the dinosaurs, this was like being provided with a telescope capable of looking back a hundred million years.
Paul Kenrick and his colleague have been looking at a group of survivors called lycopsids. In the coal swamps of the Carboniferous three hundred million years ago lycopsids grew into huge trees—their bark and roots are common fossils found in association with coal seams. Museum drawers are stacked with examples. Compared with the flowering plants, lycopsids are Methuselahs. Three surviving families are all that remain of this once great group, but these had already diverged from one another back in the Carboniferous. One of these families is the Lycopodiacea, of which only herbs survive today, belonging to three genera. One genus, Huperzia, is an epiphyte that lives its life attached to the branches of tropical trees. The other two, Lycopodium and Lycopodiella, are the club mosses, familiar low herbs on damp heaths and moors. It would clearly be interesting to know whether species of these genera are all ancient survivors, or whether they evolved more recently, perhaps alongside the flowering plants
. The living species were investigated using sequences from the gene rbcL, which had previously proved so useful for the flowering plants. Then the sequence differences between lineages were used as a kind of clock to estimate the time of divergence—that is, when they separated into distinct evolutionary lines. It was discovered that Huperzia clearly divided into two groups of species: one Neotropical in South America, the other Palaeotropical on the opposite side of the Atlantic Ocean. Furthermore, the diversification of the two groups happened in the Cretaceous, more than seventy million years ago. This is consistent with the widening of the Atlantic Ocean following the break-up of the ancient continent of Gondwana, which was the southern part of the still greater supercontinent, Pangaea. Many other plants have a similar tale to tell—evolution took on distinct trajectories once the old and new worlds had separated. By contrast, much of the evolution of Lycopodium and Lycopodiella species happened in much more recent times in the late Tertiary, different species being found in different and separate localities. So it seems that, despite their antiquity as a family, lycopsid evolution did not simply sit still. New species groups arose in response to events in geology. On the other hand, the separation into different genera probably happened as far back as the Permian 260 million years ago, and so all the lycopsids are, in another sense, living fossils. It remains true that, when one looks at these plants, one is looking back hundreds of millions of years into the geological past. The differences between species are relatively small—a matter for the expert—and the living species evidently arose as a result of geographical separation. This example shows how study of humble herbs can marry geology, fossils and molecules in a most stimulating and satisfying way. I can’t help wondering what the Great Men like Spath would have thought of it all.
Living lycopsids in New Zealand, showing a succession of vertical sporophytes, looking like little “brushes”
There is no danger of running out of new discoveries of fossils. I have been amazed by what has been prised from the rocks in China. As well as feathered dinosaurs and fossil flowers more ancient than any known previously, tiny fossilized embryos have been discovered in rocks still older than the Cambrian, the first direct evidence for animals in strata of this age. Seek hard enough, and finds shall be made; the book of the history of life must be continually rewritten. It could be argued that the recognition and naming of fossil species are less urgent than those of living animals and plants. They are not going anywhere from their sedimentary tombs—and, after all, most fossils belong to species already long extinct. This is to miss the point, for we are what history has made us. There are lessons to be drawn from the past extinctions and climatic crises that life has weathered—histories that may well equip us to cope better with the climate changes that are happening now. For example, the climatic warming of today marks a return to conditions on the “greenhouse earth” of mid-Tertiary times: suddenly the expertise of a palaeontologist who knows about this period will seem less arcane. Equally, the impoverished world that followed upon the great mass extinction at the end of the Permian period 248 million years ago provides a chilling prospect for humankind if we continue to degrade our planet in the way that we have been. This provides a pragmatic, sensible, utilitarian reason for studying the past, but one that is anthropocentric at root. I don’t want to reduce the fossil record to “lessons from history.” The real joy of discovery is to see the exuberance of life, those trilobites with tridents, or those great flying reptiles as big as gliders—organisms almost as exotic as the confabulations of Hieronymus Bosch, but thriving here on Earth long ago. To know about the wonderful excursions that life has taken is to be enriched, to be made aware of the fecundity of our small planet. This is what motivates palaeontologists to tap away for weeks on end at ungrateful rocks. This is the point of securing the booty recovered as testimony for generations of scientists to come in the drawers of the hidden museum.
4
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Animalia
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Zoology embraces all animals, not just the appealing furry or feathered varieties, so I will start with snails. Slugs and snails are regarded by some people as the least appealing of nature’s productions. As the nursery rhyme tells us, little boys are made of them, with added puppy dogs’ tails, to contrast with all that sugar and spice and all things nice that little girls are made of. But the Class Gastropoda is also one of the most diverse outside the insects and includes many miraculously beautiful coiled shells. One of the least spectacular, if most familiar, among the seashells are the little turreted winkles that one finds clustered on rocky shores. Sometimes they are found in such profusion as to make walking over the rocks a difficult business. Winkles are edible, although hard work. They are sold cooked in small tubs, and a traditional seaside delight was to “winkle” out the tough little morsels with a pin—hence the name of the pointy winklepicker shoes that enjoyed a brief heyday in the 1950s. A slightly more refined name for the little mollusc is periwinkle, but that is also the moniker of a plant, so I prefer the shorter version. David Reid in the Natural History Museum is devoted to winkles, and knows more about them than anyone. He is tall and thin, in early middle age, with a short, well-cared-for beard and glittering, intense eyes. David becomes extraordinarily animated when he talks about his favourite snails. He is to be found in the basement of the old building not far from the site of my first office. Almost all the other zoologists have moved to the new Darwin Centre, but the molluscs are still where they have always been. Such permanence is rather comforting, so when I visited David I could briefly imagine that I was still the young tyro strolling down the wide corridor with my life ahead of me. Winkles used to be placed in the single genus Littorina, the common (peri)winkle being Littorina littorea, which tells you all you need to know about its littoral—that is, shoreline—habitat. Nowadays, the winkles are divided into a number of different genera. “The great thing about them,” David enthuses, “is that you can collect them all over the world so easily. There is probably no better group to use to examine the relationship between geography and species.” Winkles do not run away when the scientist tries to catch them, they do not fall to pieces, nor do they have Threatened or Vulnerable status on conservation lists. Their flesh can be used to extract DNA readily enough. They are ideal subjects to winkle out the truth about evolution.
David Reid gathered together everything that was then known about Littorina in a huge monograph published by the Ray Society*7 in 1996, all 463 pages of it. The book is monumental. David tells me with characteristic self-deprecation that when it was published a Scandinavian colleague with less than perfect English wrote to him congratulating him on producing “a major millstone.” There must be hundreds of photographs of shells, and nearly as many of the radulae—the rasp-like “teeth” of molluscs—taken with the electron microscope, to say nothing of dozens of drawings of the penis, which is a critical character in winkles. There are details of the sculpture on the shells to help the reader identify a species in hand. It turns out that not only do winkles vary between species, but they also offer excellent examples of variation within species according to differences in habitat; winkles nestled among the barnacles will have different shells from those on more exposed rocks. In some localities there are a number of separate species on a single shore adapted to different heights above sea level. There are knobbly ones, ridged ones and nearly smooth ones. Some winkles have planktonic larvae, while others do not. In some species there is a good reason for a particular feature. For example, winkles living at high latitudes have the outer shell layer made of the form of calcium carbonate known as calcite, whereas the tropical ones tend to have the same layer made of its other form, aragonite. Calcite is less soluble in cold water than aragonite, so it makes sense to use this material in more arctic climates. Some species of winkle have to live on seaweeds; others refuse to do so. As more is learned it becomes clearer just why there are so many species of this lowly snail, and how they manage to coexist.
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Dry Storeroom No. 1 Page 12
