Dry Storeroom No. 1 (16 page)

The AHOB project is revealing Britain as one of the best places to study human history in northern Europe. Wherever new discoveries in the field are made, the materials recovered are still what they always were: fossils, artefacts and sediments. It is still necessary to get the hands dirty and to muddy the seats of trousers. Nowadays, much more attention is paid to tiny fossils of pollen grains and vole teeth than was once the case, but the importance of taxonomic expertise remains the same—you need people who know their stuff: Adrian Lister for the elephants and their relatives, Andy Currant for the voles, Russell Coope for the beetles. What is thoroughly new is the variety of techniques that can be applied to the material collected. No tomfoolery with specimens is possible now that they can be chemically analysed down to their very atoms, and their geochronology investigated using Radiocarbon dates (if they are not too old), Mass Spectrometric Uranium series, Electron Spin Resonance and Optically Stimulated Luminescence. This is white-coated laboratory science: “real” science, doubtless, to devotees of gadgets and gizmos. One of the intentions is to use oxygen isotope measurements from fossils to link the sporadic fossil record in Europe with the standard climatic cycles recognized from sampling continuously deposited oceanic sediments; ratios of these isotopes fluctuate in harmony with the ambient temperature. This provides crucial information, because early human history coincides with the climatic fluctuations of the Pleistocene, a period which began 1.8 million years ago and lasted until twelve thousand years before the present. This is a large part of the “ice age”—in fact, it comprises a whole series of advances and subsequent retreats of the northerly ice sheet.
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As a species, we always have been in thrall to climate change, as we may well be again over the next century if global warming predictions are fulfilled. What AHOB has proved beyond doubt is that mankind’s history in Britain is one of repopulation with long intervening periods when apparently no people were able to cope with the frigid conditions. They retreated southwards into continental Europe. The longest of these periods was from 180,000 to 60,000 years ago, after which humans, including Neanderthals, recolonized when the climate ameliorated. Another, younger frigid period between 22,000 and 16,000 years ago has also so far failed to yield any evidence of human occupation of Britain. Since this period included the Last Glacial Maximum, when ice extended south almost to the Home Counties, this fact may not be altogether surprising. Only after this time were our own distant ancestors, belonging to
Homo sapiens,
able to move in. If we had a notion that inhabitants of these islands were invaded by Vikings and Normans but otherwise inviolate, then it is clearly wrong. Repeated invasion has been the very stuff of our history.

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.