Читать книгу Investigating Fossils - Wilson J. Wall - Страница 8

It may seem a slightly circular argument to look at the history of an historical record like palaeontology, but this is what the history of fossils is all about. It is because fossils are so enigmatic, in both origin and wider meaning, that the way they have been interpreted is so important. Such knowledge can tell us a great deal about the social and religious changes that have taken place over the lifetime of humanity. Which, to state the obvious, in geological terms humanity is a split second on the geological time scale of our planet. It is also worth remembering that for many species the fossil record is frustratingly lacking in detail. However, we do know that living animals are a small fraction of all the species that have ever lived. Given such knowledge, it is reasonable to spend considerable time pondering the fossil record, all the progenitors of modern species. It is also reasonable to consider the development of a science that flirts with geology and yet studies ancient species, all of which are extinct.

Before any meaningful discussion could be had regarding the importance of fossils, it had to be agreed what fossils were. It was not always known that they represented organic remains, they are, after all, stone, the most immutable of material. How could a plant or animal be turned to stone without divine intervention? Whether it was to help in developing our perception of ourselves and our position in nature, or to evolution and the origins of life, the apparent anomaly of fossils had to be understood.

It may seem self‐evident to us that fossils represent remains of living organisms, but as an untestable hypothesis this is something which requires a great deal of circumstantial evidence to demonstrate as near conclusively as it is possible to get. Part of the historical conundrum which vexed the earliest of observers was that these apparently animal remains, usually bivalve molluscs, were made of stone, and yet no animal has a stone carapace or skeleton. This contradiction between living organisms and fossilised species created a number of explanations of varying plausibility to explain both origin and position. These ranged from high seas to account for high‐altitude shells, to the rocks being inadvertently seeded with the life force of the found organism that could not develop properly in its rocky environment.

Nowadays we assume that in some way a dead body can become mineralised so that it has the persistence and solidity of stone. It should be understood, though, that fossil material can originate through several different processes of mineralisation, with the final product also varying quite widely, depending on the processes that have taken place. If fossilisation is considered a method of preservation, then most fossils are not well preserved at all, only the shape is retained, a morphological ghost of a living, breeding, physiological organism. Colours are lost with the process of mineralisation as are all the intricate biochemical markers that defined the organism. As we shall see, this loss of colour has allowed for wide and sometimes bizarre interpretations, of what a living fossil species might have looked like. This is different to how the animal may have stood or moved. There is adequate information available from fossil skeletons and knowledge of living organisms to give us a clear understanding of the three‐dimensional structure of species, but not their colour. There is something else which disappears; behaviour. There is a gap in our knowledge which it is difficult to see ever being filled, and that is the intricate ecology of prehistoric times. Beyond knowing that some species were carnivores while others were herbivores, details which can be inferred from teeth and skeletons, interactions are hidden by time.

While for most the idea of a fossil is of mineralised bones, it does not necessarily have to be so. The meaning of fossil has subtly altered over time from its original Latin root of fossilis, which translates as ‘obtained by digging’ through any found material to its current usage of preserved material, or possibly more accurately, preserved organic material. Using this definition, entrapped organisms in amber also constitute fossils, in this case with much more information preserved than simply a shape; but great caution should be exercised with this idea. The ideas put forward by Michael Crichton in his novel Jurassic Park (1990) may be very appealing, but this is just an imaginative fiction. There may well be preserved organic molecules in amber‐encapsulated specimens, but within any cell upon death DNA will rapidly start to break up into smaller pieces with increasing entropy. Although there is conflicting evidence regarding DNA decay, preservation in frozen material seems to be best, while long‐term preservation in fossilised material seems less and less likely. Work on DNA decay in relatively recently extinct species, such as Moas from the southern hemisphere, has given an insight into the rate of disintegration and associated bacterial contamination (Oskam et al. 2010; Allentoft et al. 2012). All these biochemical analyses and insights are, of course, in addition to the implausibility of a blood‐sucking insect of the right type being caught in amber. A better chance of finding longer strands of DNA from ancient extinct species comes with the sometimes ignored natural preservation technique of freezing. This is the situation commonly found in permafrost.

There are some very good cases of preserved remains, most notably mammoths, in permanently frozen ground. The excitement that such discoveries produce is not confined to the past, and neither is it confined to scientific circles. In May 2013, a preserved woolly mammoth was discovered in Siberia and became widely reported, including in the UK press (Daily Mail 2013). So common are mammoth remains found that there is a well‐developed trade in the tusks, known as ‘ice ivory’ and in 2018, there were reported to have been more than 100 tonnes traded, usually for carving into small pieces in the far east. This trade has become so widespread that it has become a concern that poached ivory is being smuggled and traded within the ‘ice ivory’ trade (Cites 2016, 2019).

The mechanisms of taphonomy, which is the process which results in a mineralised fossil, have been difficult to nail down. This is at least in part because fossilisation is not a single process. A fossil can come about through many different routes, but always involves a set of unlikely conditions and complicated geochemistry. This is well shown by Thomson (2005). We would like to fully understand this process as our knowledge of evolution stands on the foundations of the fossil record. Studying the mechanism of taphonomy is in itself a recent aspect of palaeontology and one which is intimately associated with the geology of the land. It is this linking of conditions and geology which has resulted in such large and high‐yielding fossil beds as are found in China, Mongolia and the USA.

It is easy to understand that without a process of fossilisation, there would be no fossils and so we could only speculate, devoid of evidence, as to what had lived and breathed on our planet in bygone aeons. In fact, under such circumstances, we may not even consider that there had been species before those that are currently extant. Without the existence of fossils we would have no easily recognised method of aligning the age of the Earth to reality. This would render myths about God creating the planet in seven days and its associated fantasies, difficult to gainsay. However, we do have fossils and so we do recognise the age of the earth as much greater than we can easily comprehend.

It is the human scale of perception of time which made it easy to persuade people that the creation of the Earth happened only a few thousand years ago. By having a version of events which was just about on a conceivable time scale, it made the whole story plausible, which having to think in millions of years was not. Even so, this Biblical explanation involves a period of time which is almost unimaginable when compared to the lifetime of an individual or the social memory of a family. Nonetheless, it is much shorter than thousands of millions of years, which in truth is a scale that really has no meaning to the individual, or even in terms of the life cycle of a species. Species come and go, the average lifespan of a mammalian species seems to be between one and two million years (Mace 1998). This is why palaeontology is so close to geology, it extends so far back in time that only the rocks tell the story, but it is pivotal in the study of the origin and evolution of life.

Part of the modern fascination with fossils stems from the same conundrum with which they were first approached; how can an organic, living being, be converted to rock? The idea that a fossil was the imprint of a living thing made into stone did not gain broad traction within the general population until the nineteenth century, even though it had been voiced prior to this. It is also true that the essential problem of admitting fossils as being mortal remains transmuted into stone was putting science into direct conflict with the Church.

Most early naturalists, and nascent palaeontologists, had gained a classical education, many having been ordained clerics, so there was a long history of reluctance on their part to accept the idea of fossils as organic remains. Such an idea would be in direct conflict with their faith, or at least their education. There was, as a consequence, a long period of published ideas that tried very hard to roll the idea of fossils into a corner where they could be explained away as artefacts or accidental productions of nature, but certainly not the remnants of long extinct species. These arguments were used by Plot (1705) to explain many of the fossils that he found in Oxfordshire.

A change in general attitude towards the nature of fossils took place in the nineteenth century with the parting of the ways between Romanticism and science. Romanticism found its place in the self‐indulgent imagination of literature, while the educated imagination of science stood against the idea of assumptions, like those promulgated by religion. It was the broadly untestable ideas of history, which had stood as untested mythical explanations for centuries that were going to yield to the new inquisition of scientific thought. Scientific investigation of fossil material was fuelled by a need to build a consistent picture of the world, which would always be open to challenge as new information arose, but a picture which by its very nature would allow for predictions that could be tested. This was exemplified by the work of Lyell (1832).

Just as we sometimes forget that nobody has seen a living dinosaur, it is also true that nobody has seen the process of fossilisation, that extraordinary series of changes from soft organic to immutable solid. The very indestructibility of stone was part and parcel of the original problem of thinking that fossils could be plant or animal in origin. Even when they were clearly recognised as biological in origin, the questions that were raised were difficult to answer, indeed, they were in some quarters seen as heretical even to ask. The questions immediately associated with fossils were not necessarily at odds with the Biblical story of genesis. For example, if fossils were the remains of animals which were obviously akin to sea animals, how could they be found at the tops of mountains and among cliffs? Several different suggestions were made, the two extremes being that the sea level had dropped (Leonardo Da Vinci, Notebooks 1880) or that earthquakes had raised the mountains (Robert Hooke 1668). Such ideas only held for those species which were obviously marine, problems with skeletons of creatures that ostensibly walked the earth were so mired in difficulty that for the most part such skeletal remains were ignored or put down as unusual rock formations.

Besides the positioning of fossils, there was another problem that vexed both the Church and philosophers. If, as seemed likely, fossils were products of the organic world, both of plant and animal material, they were not like anything currently known. So if they did represent animals or plants, then there would have to be a concept of extinction. This flew in the face of the Bible where creation had taken place as a representation of perfection, and there were neither deletions nor additions of plants or animals possible. As a by‐product of this logic, neither were those species that were found, capable of change. If there were extinctions or additions to creation, but most notably extinctions, the implication was that God had made a mistake and had a few attempts at creation before coming up with the final version. Some of this could be partially explained away by assuming that species changed over time. This possibility of a mutable species required a certain flexibility in ecclesiastical interpretation, which was not always possible in some churches.

Even assuming some ability to change, the radical nature of some fossils was difficult to explain in this way. They were just so different, accepting that they had a biological origin would require a big step towards accepting extinction as a real possibility. So another attempt at explaining the animals found fossilised, without treading on ecclesiastical toes, was to suggest that fossils represented species which had died in that locality, but were still extant elsewhere on the planet, or perhaps they had been washed there during the Flood. It was not so difficult to entertain the idea of a species still being alive elsewhere as the planet was ostensibly a much bigger place than it is now. Travel was difficult and slow, indeed there were many areas which remained unexplored until well into the twentieth century. To the explorers of the eighteenth and nineteenth centuries, the immense scale of the Earth left the feeling that there were hiding places where these species, known only from fossils, could be found.

There is one example of this strange phenomenon of a species being known from fossilised remains and then being rediscovered later. Strictly speaking it is a descendent of the assumed extinct lineage which was rediscovered, rather than the same species. This is, of course, the Coelacanth. This astonishing story started in December 1938 when Marjorie Courtney‐Latimer was on a trip to the dockside of East London in the Eastern Cape of South Africa, to see what the trawlers had brought up by way of specimens for the East London Museum of which she was a curator. On this particular occasion what she found was a 1.5 m, 57.7 kg fish that was already a day out of water. It had been caught at the mouth of the Chaluma river, just south of East London. Through many trials and tribulations it became apparent that this was a fish representing a lineage that had been supposed extinct for 80 million years. Identification came a few days later as a member of the Coelacanthiformes, a group previously considered extinct. Even more astonishing was that this put it into the Crossopterygii, the otherwise extinct group of lobe‐finned fish. This particular species was described and appropriately named Latimeria chalumnae (Greenwood 1988). Such a find is a very rare occurrence as it was not a rediscovery of a species, or even just a new discovery of a previously unknown species, this was finding a group of fish that were well known from the fossil record and assumed to have disappeared millions of years previously. If L. chalumnae had been discovered in the eighteenth or nineteenth century, this would have been used as a demonstration by biblical literalists and supporters, that the fossil record was of species still extant, but not yet found. There are two points to be made about this, the first is that the oxymoron ‘living fossil’ is misleading and the other is that as far as we know L. chalumnae was not represented in the fossil record, it was the lineage which had survived, rather than the species. Another such surviving ancient lineage is the Tuatara, Sphenodon punctatus, from New Zealand. This has been the subject of a quite recent debate regarding the status of a living fossil and the very concept of a ‘living fossil’ as a useful idea, rather than a confusing one (Vaux et al. 2019).

The situation with the Coelacanth is a very unusual event, although really not so surprising when you consider the numbers involved. As there are generally regarded as being something between 1.5 and 4.5 million species extant on the planet (there are very good biological reasons for this wide range) while through the whole Phanerozoic aeon, which is approximately 541 million years, we have so far found fossils of only about 250 000 different species. This also demonstrates something else; we have no idea of the level of biodiversity for most of the past. We can only surmise what the range of animal and plant species were. There is certainly no reason to believe that the biodiversity was significantly less than it is now. The number and range of species in any ecology will determine the stability as well as the complexity of the population. It is for this reason we have to assume that in the past biological radiations have occurred to fill ecological niches adding to both the complexity and the stability of the system. The complexity and diversity present in the palaeontological ecosystem are reflected in the rate at which dinosaurs are being discovered. In 2019, there were more than 30 new species described and based on mathematical models, this is a small fraction of the potential, with anything up to 70% still to be discovered.

There is no reason to believe that fossilisation is a process only of the past, sedimentation is taking place all the time, with concomitant rock formation, so there should be fossil formation at the same time. Since we do not have a continuous collection of recent fossils from extinct species such as Dodo, Great Auk or Quagga, we can reasonably assume that using a fossil record as a determinant of species numbers is likely to lead us far from the true number. We can, however, make a calculated guess at the diversity from looking at modern ecosystems of the same broad type as we would have expected in any similar area in ancient geological time.

With the developing interest in palaeontology among the general population and the apparently human tendency to collect things, fossils have become ever more important. They have developed an importance, from a scientific point of view, in helping us understand the way species develop and lineages change, or like the clade of Crossopterygian fish, pass through time largely unaltered. Studying fossils can even help with developing completely new ideas and lines of reasoning, such as how birds originated. As part of this they can help immensely in understanding the biggest and most important questions in biology; evolution and the development of modern species.

At the same time, the human urge to collect and make sense of material goods, stamps, coins or fossils has meant that they have become of far greater commercial importance than would have been dreamt of 100 years ago. Wealthy collectors can pay large sums of money for rare and exotic fossils, probably far more than their scientific value merits. This can in itself generate problems, such as scientifically valuable fossils being removed from public view and scientific research. Another problem that can arise is that in the base commercial environment within which we live, it is seen as quite in order to generate chimaeric, or even just plain fraudulent, fossils for sale. Of course, this is not new or confined to fossils. Neither is it a phenomenon limited to areas where the outcome of discovery would be predominantly embarrassment, like faked paintings. When Isaac Newton joined the Royal Mint and supervised the recoinage of Britain in 1696 (there was no paper money), it was estimated that between 10 and 20% of the coins in circulation were counterfeit. Even these examples can be seen as relatively minor compared with the wholesale perversion of scientific knowledge when fraud in science takes place.

Some forms of scientific fraud can be seen as relatively harmless, motivated purely by money, this would be where a fossil has been embellished to make it more valuable, but has little intrinsic palaeontological interest. When wholesale fraud takes place, which disrupts the flow of knowledge, then the fraud becomes far more serious. Strangely, the currency of knowledge is held as of less importance than the currency of gold where this sort of fraud is concerned. Interestingly biological fraud has appeared in many different and sometimes surprising places. An example of financially motivated biological fraud is described in the broadly autobiographical book Papillon by Henri Charriere (1970). In this book he describes how, having escaped to British Guiana (now Guyana), he produced an apparently hermaphrodite butterfly by putting male wings on a female body. He further describes how he then sold the specimen to an American for $500. All this took pace in 1941 when the median annual salary for an American was just under $1000. Even then, during World War II, such productions were a profitable enterprise. It is worth considering the problem of a specimen that is genuine, but is so outlandish that it was thought it might have been a hoax. This was the situation as it occurred with the Platypus, Ornithorhynchus anatinus. When a dried specimen was looked at in detail and first described in 1799, it was thought that it might be a hoax. Such composite animals had been known to have been produced by skilful taxidermists in the far east as representations of mythical creatures (Moyal 2004).

In an era when data can be promulgated very quickly, retractions and rebuttals do not necessarily have the same weight as the original message. In these circumstances, fossil fraud can have far greater repercussions than simply questionable science or making dishonest money. Fraudulent fossils may become part of a spurious line of reasoning about creation or evolution and no amount of denial of the obvious lack of veracity of the image of, say, a fossilised giant will counter the belief systems of the ignorant.

Knowledge of fossils cannot be given a start date, as soon as man came into contact with suitable geological areas fossils would have been seen. The cognitive recognition of them being biological in origin may well have come later, certainly as soon as writing became more than simple accountancy. It seems that in the ancient world around the Mediterranean it was easy to slot some of the large bones of fossilised mammals into the mythology, labelling them as being the skeletons of ancient giants and warriors. Because fossils are not confined to one area of the planet, it has taxed the minds of all nations to find an answer to how obviously marine species come to be found so far up mountains. It was only later that people started asking questions about the process of fossilisation itself. The process of fossilisation does take a great deal of understanding and to some extent speculation, since even for short fossilisation periods, it is still far too long when compared to a human lifetime.

Understanding the biological, rather than mineralogical, origin of fossils was a first step in a practical attempt to explain the process of fossilisation. To turn biological material, which everyone knows decays, into a form of rock as solid and stable as any rock, was difficult to comprehend. Once this was understood, at least in part, to be possible, the position of fossils as pointers to the past became undeniable. That we now had a series of items which indicated that species had come and gone, that life had a history and was not brought into being fully formed, made it possible to think of species as being rather more plastic than the ideas of immutability would have had us believe. With that knowledge, species, both fossil and extant, could take their central place in describing evolution.