Opponents of evolution are always talking about gaps in the fossil record. What are they referring to?
When we have a group of living organisms that is differentiated from its nearest relatives by a whole suite of traits, evolution predicts that there were formally ancestral organisms that had some but not all of these traits. These are called “transitional fossils.” In some cases we lack fossils that document all the steps in the evolution of the suite to traits found in a living group. Such missing steps are “gaps.” Over time the number of such gaps has been reduced greatly. For example, many intermediates have been discovered, such as vertebrates with some but not all the features of the land-dwelling tetrapods, dinosaurs with some but not all the features of birds, land plants with some but not all the features of vascular plants. Nonetheless, there are still some cases where we would very much like to find additional transitional fossils: for example in the origin of bilaterally symmetrical animals and the origin of flowering plants.
