For an explanation, see the main splats page
The principles of fossils
- Fossils are traces of old life forms which need to be interpreted, allowing for changes in death, and the warping caused by the compression of sediments.
- Some fossils are too important to be left in private hands, which is why many fossil sites are off limits to amateurs who are likely to do more harm than good.
- The best fossils are formed from living things when the material of a live organism is replaced by other material that is fine-grained and slow to deposit.
- When conditions are just right, dead animals and plants may be preserved in sedimentary rocks. Over time, these fossil remains are chemically changed.
- When an animal dies, the long bones and the skull contain marrow and brain, and will be worked over by scavengers, so little remains of those bones.
- When an animal dies, some parts like the mandible (jaw), finger and toe bones, and the ends of the long bones, offer little nutrition and are usually left.
- Many fossils form by chemical replacement, where the material of the living organism is replaced by other, longer-lasting material, unrelated to the organism.
- Decayed plants may leave phytoliths as traces, and these can be recovered from deposits and used as hints on previous climates and crops by archaeologists.
- Some fossils form when bones are buried, and over time, the mineral material of the bones is replaced by other chemicals, even opal, dissolved silica.
- A stromatolite is a very ancient fossil form which is still around today. They date back to at least 3.5 billion years, possibly 3.8 billion years.
- The Burgess Shale of Canada contains very unusual fossils, as does the Ediacara formation of Australia, because they represent Precambrian forms.
- In 1947, geologist R. C. Sprigg discovered a rich deposit of Precambrian fossils in the Ediacara Hills of South Australia, the 'Ediacaran fauna'.
- Sometimes, a living fossil may be found: this is an animal or plant that was previously known only from fossils, and which is now found to still exist.
- Examples of living fossils include the ginkgo tree of China, the coelacanth of Africa (and more recently, Indonesia), and the Wollemi pine of Australia.
- There are many fossil types: some are formed when something rots away, leaving a mould that can be filled by minerals in groundwater, seeping slowly in.
- Very few things that die will ever be fossilized, as the dead animal or plant must be buried in oxygen-free conditions, and quickly covered by fine sediment.
- Fossils tell us what the past was like, the types of plants and animals that lived in an area at the time when the fossil-bearing sediments were laid down.
- Similar deposits in different areas may be linked by stratigraphic correlation, by looking for marker beds, identified by unusual minerals or fossils.
- Rocks which contain fossils of the same species are usually similar in age, and for this reason, fossils are often used to correlate strata over wide areas.
- Living things may perform the same function in different ways: lungs, gills, spiracles and diffusion are all used to supply oxygen in different groups.
- Legs in different animal groups are quite different in structure, even if the same homeotic genes are involved, and even if they serve much the same function.
- Arthropod legs have an exoskeleton with internal muscles, while vertebrate legs have an endoskeleton: presumably these two forms of leg evolved independently.
- In 1695 John Woodward published his 'Essay toward a Natural History of the Earth', saying that fossils formed when Noah's flood destroyed the Earth's surface.
- 1696 William Whiston published his New Theory of the Earth, which suggests that Noah's deluge might have been caused by a comet striking the Earth.
- In 1705 Robert Hooke's posthumous 'Discourse of earthquakes', completed 1668, speculated on the geological mechanisms responsible for the fossil distributions
- In 1787, Caspar Wistar described in Philadelphia a large bone, said to be a thigh-bone of a large animal, almost certainly duck-billed hadrosaur.
- Wistar's fossil has since been lost, but given the source, and Wistar's anatomical skill, it must have been a thigh-bone, and the first dinosaur bone known.
- In 1796, Georges Cuvier attributed the succession of fossil forms to a series of simultaneous extinctions caused by natural catastrophes, one of them Noah's flood.
- Georges Cuvier argued that the whole of an organism is to a pattern that is defined by its way of life in a predictable way, that every organism forms a whole.
- Cuvier argued that if the intestines of an animal are so organized as only to digest fresh meat, then jaws, claws, teeth, even legs and senses will match this.
- In 1823, William Buckland published his Reliquiae Diluvianae, in which he argued that fossils were formed when caves filled with mud during Noah's flood.
- Mary Anning of Lyme was a self-trained palaeontologist of the early 19th century, who found and prepared many famous fossils to sell, living on the proceeds.
- Mary Anning, fossil finder, features in the nursery rhyme "She sells sea shells by the sea shore, and the shells that she sells are sea shells, I'm sure."
- In 1913, Hans Reck discovered rich deposits of early mammalian fossils at Olduvai Gorge in East Africa, which would later take the Leakeys there.
- In 1917, Ferdinand Broili discovered the fossil remains of Seymouria, an organism showing both amphibian and reptilian characteristics, a missing link.
- Fish established the first tetrapod body form for vertebrates, the four-limbed body adopted with variations by amphibians, reptiles, birds and mammals.
- In 1932, A Danish scientific expedition found ichthyostegid fossils in Greenland. These were the oldest known fossils that can be classified as amphibians.
- In 1938, a live coelacanth was found off the coast of southern Africa. In 1998, another population of live specimens was found near Indonesia.
- Reconstructing fossils, a form of forensic reconstruction and preparation which adds flesh back to bones in a plausible way, is a skilled task.
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