Fossils are the preserved remains of living things and the fossil record is all the data that scientists have collected from fossils about past life. The fossil record can show how organisms have evolved over time and can also show the relationship between different organisms. By examining fossils scientists can note patterns of development or similar body structures between organisms that show that they may have a evolved from a common ancestor. For example, even though dolphins, birds and dogs look very different they share some physical characteristics which we call homologous structures. The bones in the flipper of a dolphin, wing of a bird and leg of a dog are very similar. These similarities provide evidence that these organisms evolved from a common ancestor. The fossil record shows us that birds are ancestors of dinosaurs! By comparing fossils of different dinosaurs of the past we can see many relationships between modern day birds and ancient dinosaurs including feeding mechanisms, bone structure and feathers (or the beginnings of feathers). A cladogram or branching tree show the relationship between organisms and their ancestors based on common characteristics.
fossil of Archaeopteryx, a primitive bird