Macroevolution Chapter 18

Fossil Records  By the 1700s, fossils were accepted as evidence of ancient life.  Despite being accepted, the interpretation of the fossils was somewhat questionable for many years.  Fossil records were used to support cultural beliefs for a long time.

 Ex: A man found the remains of a salamander and pronounced it as evidence of a man killed in the Great Flood.  Eventually, scholars began to question the origin of fossils.

 Today fossils are being analyzed in amazing ways.  The purpose of studying a fossil record is to get an idea of lineage, or how certain animal lines developed.

 Fossils are recognizable evidence of ancient life.  Fossils include bones, teeth, shells, seeds, spores, etc…  Imprints of leaves, stems, tracks, trails, and burrows are indirect evidence of ancient life.

 In some cases, fossilized feces (coprolites) can give an indication of what species were being eaten during a time period, which in turn allows us to know what species were alive at that time.

 Fossilization starts when an organism gets buried under some type of sediment – volcanic ash, at the bottom or a body of water, etc…  As water enters the organism’s body, metal ions and inorganic compounds enter the body.

 As more sediment accumulates over the body, pressure increases.  Because of the compounds and pressure, the bones are converted to a stone-like hardness.  Fossilization is best when an organism was covered rapidly and away from oxygen.

 Sediments occur in layers due to the deposition of ash, silt, or other minerals on top of each other.  The layering is called stratification.  Deeper layers formed longer ago, while shallow layers were formed recently.  The older the layer, the older the fossils

 Currently, there are 250,000 known fossilized species.  Judging from this diversity, there were probably several million types of ancient species, now extinct.  The fossil record is, however, incomplete.

 Many soft-bodied species were not fossilized, and species with low reproduction rates were also not abundant in the record.  Certain environments are not conducive to making fossils, and much of the earth is covered in water – making it very difficult to search for fossils.

 Using the fossil record, scientists were able to study comparative morphology.  This is when the anatomical features of related species are studied and compared.

 When populations of a species get separated, they can change over time. (allopatric speciation)  The two groups will diverge genetically if enough time is allowed to pass.

 The change in body form from a common ancestor is termed morphological divergence.  When related species diverge in form, they remain common in other ways.

 When one or more body parts are similar in different species, the organs are considered homologous.  If they are similar enough, they probably had a common ancestor.

 All species have a mix of new and ancestral traits.  The kinds and numbers of traits they do or do not share determines how closely related species are.

 DNA is unique to a species.  It has the information to make proteins using RNA.  Therefore, DNA is an additional way of figuring out the evolutionary relationships among species.

 Species who have closely related DNA are probably related closely.  Studies can be conducted in two ways:

1. Protein comparison – species have the ability to make proteins. The mechanism in which the protein is made is unique to the species.  By comparing the ability to make one certain protein, scientists are able to determine how closely related species are.

2. Nucleic Acid comparison – the extent to which the strand of one species of base pairs is like the strand of another species can determine how closely related they are.