Palaeontology is the study of fossils. It is a very important branch of biology, because evolutionary ancestors all died long ago and fossils provide us with our only direct evidence of the animals and plants of the distant past. If we want to know what our evolutionary ancestors looked like, fossils are our main hope. As soon as people realised what fossils really were - previous schools of thought had held that they were creations of the devil, or that they were the bones of poor sinners drowned in the flood - it became clear that any theory of evolution must have certain expectations about the fossil record.
We are lucky to have fossils at all. It is a remarkably fortunate fact of geology that bones, shells and other hard parts of animals, before they decay, can occasionally leave an imprint which later acts as a mould, which shapes hardening rock into a permanent memory of the animal. We don't know what proportion of animals are fossilised after their death - I personally would consider it an honour to be fossilised - but it is certainly very small indeed.
