Part 1 - basic ideas and concepts
These pages are an introduction to several themes and subjects of my own research, written in a style and using a terminology that should be understandable to an educated non-specialist. Please note that these pages are not meant as a general course in palaeobiology or functional morphology, but rather as a presentation of my own research to a non-specialist but educated public.
The level of specialisation of these materials increases gradually throughout these pages. Concepts and term introduced in this discussion often are necessary to understand materials presented at a later stage, so you should follow the order in which these pages are linked. References to my scientific publications dealing with the same subjects, or to other relevant publications, are provided at the bottom of each page.
1 - A basic introduction to fossils and fossilisation
This section may be useful as a general introduction. In order to follow this discussion, you need a basic knowledge of scientific concepts, which is not provided here but can be acquired elsewhere on the World Wide Web, public libraries, museums, or schoolbooks. If you already master the basic concepts of Earth science, fossils and evolution, you may safely skip this section.
During the geologic history of the Earth, several phenomena gradually break down rocks. Such phenomena include rain, wind, running water, waves, changes in temperature and the activity of organisms. Rocks become physically fragmented into pieces of varying sizes (silt, sand, pebbles, boulders etc.). This process often is accompanied by chemical reactions that change the composition of the minerals contained in the rock. For instance, limestone can be dissolved by carbonic acid contained in rain water, and re-deposited elsewhere. All these processes are aspects of the the general phenomenon of erosion.
These processes, the way they interact, and the way some of the eroded material is "recycled" and forms new rock, are highly complex, and are the subject of study of several fields of Earth science. Here, it suffices to say that the products of rock breakdown are usually transported by water, wind and/or biologic activity into other environments, and deposited there. At first, these deposits (called sediments) consist of loose material like sand, mud and gravel. As time passes (on a geologic scale, i.e., across time-spans usually ranging from thousands of years to hundreds of millions of years), sediments may become consolidated and lithified (i.e., transformed into stone).
Often, the remains of dead organisms are buried together with these materials. When conditions are favourable, the remains of organisms buried in sediments are preserved, and become fossils. There is no clear-cut instant in which the remains of an organism cease being this, and start being a fossil. Depending on the type of organism and sediment, the process of fossilisation takes from thousands to millions of years. Biological remains which have not quite become fossils are called subfossils. The distinction between dead organisms, subfossils and fossils, however, remains somewhat subjective.
In general, not all parts of an organism are preserved as fossils. Most often, only skeletal, mineralised structures, like seashells and bones, are preserved. Sometimes, these mineralised parts are broken down and/or disarticulated before being buried (this is common, for instance, in vertebrate skeletons). Fossils may be preserved as original materials, or as imprints preserving the original shape but consisting of minerals of different composition and origin. Microstructures in fossils can also be different from the original ones.
Organic parts are more perishable than mineralised skeletal parts, and often they decompose before of shortly after burial. In some sediments, all biological structures are destroyed, including skeletal parts, and no fossils are found. In others, even fine organic structures are preserved in detail. In exceptionally good (but unfortunately, very rare) cases, fine microscopic detail of soft tissues, like muscle fibres, can be observed. Organic molecules sometimes are preserved, and, in rare cases, nucleic acids can be extracted and allow genetic studies. Some sedimentary beds contain abundant skeletal fossils, like shell beds and coquinas (i.e., sediments composed mostly of skeletal fossils, with little sedimentary matrix), but commonly fossils constitute only a minor portion of a sediment. Some types of microfossils and nannofossils are exceptions, and the bulk of certain sediments consist of their fossilised skeletons.
Palaeontology (spelled paleontology in North America) is the science that studies fossils, or more in general the evidence for life during the past Earth history. In the scientific literature, you are likely to encounter specific terms indicating different fields within palaeontology. For instance, palaeoecology studies past environments and their inhabiting organisms, and taphonomy the processes that take place between the death of an organism and its recovery as a fossil. The term palaeobiology (paleobiology in North America) often is used to indicate the study of fossils in a biological and evolutionary context, as opposed to "traditional" palaeontology, which may concentrate on taxonomic, stratigraphic and descriptive aspects.
Central to palaeobiology is the concept of evolution. Enormous amounts of scientific evidence have accumulated to support the idea of biologic evolution, and to explain the fundamental ways in which it works. Although numerous aspects of the evolutionary process are not fully understood, and the details of evolution within many groups still need investigation, there is a universal consensus, within the scientific community, that the basic phenomenon of biologic evolution is proved beyond any reasonable doubt, has taken place throughout the fossil record and in all groups of organisms, continues at present, and is the principal cause of biological diversity in the past and present.
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