Palaeontology is the study of fossils, the remains of past life preserved in old sediments. Throughout geological time, there have been marked changes in the dominant animal and plant groups, while the total range of physical environments has changed very little.

In some instances, the changes in the fauna and flora are the result of progressive evolutionary changes in particular fossil lineages, but much more commonly the fossil record shows that many organisms become widespread soon after they first appear; they may then flourish for a while before they become extinct and are replaced by another form. This changing pattern of forms of life in similar habitats is the basis for this book.

In a small village in western Newfoundland, I used to play cards with the schoolmaster's father in the evenings. I am sure he was the most intelligent man in the village. After I had been there for some time, he plucked up enough courage to ask me why I was not looking at the rocks up on the ridge where the old gold mines were. I told him I was not looking for gold, but (reaching into my bag and pulling out a slab of rock containing brachio-pods) "I was looking for these". He studied the slab carefully and said, "Are these sea shells?" He had never seen a fossil before, nor even heard of fossils. This question reminded me of the best of the early eighteenth century palaeontologists. But my friend went on: '"Does that mean the sea was once up here?" When I had replied "Yes", he then asked: "How long ago would that be then?" He clearly had all the makings of a first-class scientist. I replied, with a perfectly straight face, "About 450 million years ago", but I was not at all prepared for his final remark, "You'll be an atheist then".

This conversation demonstrates the type of questions asked by contemporary palaeontologists: Are these fossils marine? When and how did these animals live? What factors controlled where they lived?, and, though not really within the scope of this book, Why do they each have characteristic structures and shapes?

Plenty of books have been written on fossils, but in this book fossil assemblages, rather than individual genera or species, are the units of study. Only a selection of these is illustrated. Many fossils are not mentioned, for this book is not a treatise. Its main purpose is to educate and stimulate, rather than to describe every known fossil. We hope it will make the reader think about fossils in new ways, and lead to a better understanding of past life. Nowadays, most major fossil groups have been described (see, for example, the Treatise on Invertebrate Paleontology, (Ed.) R.C. Moore and C. Teichert, and Vertebrate Paleontology by A. S. Romer) and the most exciting and significant advances in palaeontology are being made by considering fossils as animals, and not just as formed stones. The study of Palaeoecology includes attempts at reconstructing the relationships between organisms and sediments and the interactions between organisms, including those with no close relatives now living. This has direct implications for palaeogeography, stratigraphy, and certain aspects of structural geology (like the development and evolution of sedimentary basins, and the recognition of old oceans). In addition, the knowledge of past environments and their inhabitants has important contributions to make to evolutionary biology and to the whole history of the Earth.

The selection of communities illustrated in this book has been largely based on those found in the British Isles, but the range is such that most marine fossil communities throughout the world have some close parallel with a community illustrated here.

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