AMNIOTE EVOLUTION A cladogram shows the evolutionary relationships between groups of organisms. The diagram shows how scientists believe the major groups of amniotes (reptiles and the organisms that evolved from them) are related. Time is shown on the Y-axis of the diagram. When geologists search through rock layers for fossils, they find the oldest rocks on the bottom and the newest rocks on the top. In the cladogram, the earliest organisms to evolve appear at the bottom and the most recent to evolve appear nearer the top. If the line representing a group of organisms continues all the way to the top of the diagram, which represents the present time, there are still animals in that group alive today. If the line stops before the present time, all the members of that group are now extinct. When a line branches, this shows that I group of animals, called a common ancestor, is splitting into 2 groups. The more recently two groups have had a common ancestor, the more closely related they are. Examine the cladogram and answer the questions. 1. 2. 3. 4. 5. 6. 7. 8. Which group is the common ancestor of all the other groups on the chart? What groups became extinct without leaving any descendants? Which groups have survived until the present day? Which groups that have survived until the present day are most closely related? Why? Are crocodiles more closely related to lizards and snakes or are they more closely related to turtles? Which group is least closely related to the other groups? (Which group branched off from the common ancestor of all the others first?) Which group is the common ancestor of birds and crocodiles? All the groups on the diagram except the mammals and birds are classified as reptiles. Which group of reptiles is least closely related to the other reptiles? 13
Evolution
The history and science of origin and evolution comprise two events, the beginning of life and expansion of life. Our earth originated about 4.5 billion years ago. The term evolution is derived from two Latin words and means the act of unfolding or unrolling. English philosopher Herbert Spencer first used it. Evolution is defined as the change in heritable traits of biological populations over successive generations. These traits are the manifestations of genes that are passed down from parent to offspring during reproduction.
Cladistics
Cladistics is a technique in the classification of organisms, where they are grouped into different clades. The proof for the relationships that are hypothesized is based on the shared derived characteristics known as synapomorphies. These characteristics do not exist in many of the distant ancestors and groups. The common ancestor along with its descendants is considered to be a part of the clade. The rate of closeness is directly proportional to the cladistic grouping and is useful in analyzing the evolutionary mechanism.
Outgroups
Outgroups are significant in studying cladistics or phylogenetics (that describe the evolutionary relationship between different organisms). Further, it is also important to understand the differences and similarities between different organisms.
Taxonomy
It is the branch of biology that works with the identification of organisms at first, then naming, and classification of them into phenetic or phylogenetic groups (a classification system). In other words, it is the scientific study of biological diversity and a part of systematic biology.
Phylogenetics
Phylogenetics is the scientific study of how various groups of organisms are related at the evolutionary level. It finds the relationship between various organisms based on their evolutionary similarities and differences. It is a part of the taxonomy. Although the taxonomic study is not only concerned about phylogeny but taxonomic studies are also concerned about the classification and nomenclature of the different individuals from different taxon.
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