Nomenclature & The Tree of Life

Systematics Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time.

Why Classify? In binomial nomenclature, each species is assigned a two-part scientific name. The goal of systematics is to organize living things into groups that have biological meaning.

Why Binomial Nomenclature? By using a scientific name, biologists can be sure that they are discussing the same organism. Common names can be confusing because they vary among languages and from place to place. For example, the names cougar, puma, panther, and mountain lion can all be used to indicate the same animal— Felis Concolor.

Binomial Nomenclature The first part of the name— Ursus—is the genus to which the organism belongs. A genus is a group of similar species. The genus Ursus contains five other species of bears, including Ursus arctos, the brown bear or grizzly bear.

Binomial Nomenclature The second part of a scientific name—maritimus for polar bears—is unique to each species and is often a description of the organism’s habitat or of an important trait. The Latin word maritimus refers to the sea: polar bears often live on pack ice that floats in the sea.

Linnaean Classification Linnaeus also developed a classification system that organized species into a hierarchy, or ranking. Kingdom, Phylum, Class, Order, Family, Genus, Species

Our Classification

Kingdoms The six-kingdom system of classification includes the kingdoms Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia

Three Domains A domain is a larger, more inclusive category than a kingdom. Under this classification there are three domains – Bacteria Archaea Eukarya

Three Domains

Tree of All Life

Domain Bacteria Members of the domain Bacteria are unicellular and prokaryotic. This domain corresponds to the kingdom Eubacteria. Their cells have thick, rigid walls that surround a cell membrane and contain a substance known as peptidoglycan.

Domain Archaea Members of the domain Archaea are unicellular and prokaryotic, and they live in some extreme environments. Many of these bacteria can survive only in the absence of oxygen. Their cell walls lack peptidoglycan, and their cell membranes contain unusual lipids that are not found in any other organism.

Domain Eukarya The domain Eukarya consists of all organisms that have a nucleus. It comprises the four remaining kingdoms of the six-kingdom system: “Protista,” Fungi, Plantae, and Animalia.

“Protists” – Unicellular Eukaryotes Recent molecular studies and cladistic analyses have shown that “the eukaryotes formerly known as “Protista” do not form a single clade. Current cladistic analysis divides these organisms into at least five clades. Since these organisms cannot be properly placed into a single taxon, we refer to them as “protists.”

“Protists” Most “protists” are unicellular, but one group, the brown algae, is multicellular. Some “protists” are photosynthetic, while others are heterotrophic. Some display characters that resemble those of fungi, plants, or animals.

Fungi Members of the kingdom Fungi are heterotrophs with cell walls containing chitin. Mushrooms and other recognizable fungi are multicellular, like the ghost fungus shown. Some fungi—yeasts, for example—are unicellular.

Fungi Most fungi feed on dead or decaying organic matter. They secrete digestive enzymes into their food source, which break the food down into smaller molecules. The fungi then absorb these smaller molecules into their bodies.

Plantae Members of the kingdom Plantae: are multicellular, have cell walls that contain cellulose, are autotrophic (can make their own food).

Animalia Members of the kingdom Animalia are: Multicellular Heterotrophic (get their food from external sources). Animal cells do not have cell walls.

Evolutionary Classification The goal of phylogenetic systematics, or evolutionary classification, is to group species into larger categories that reflect lines of evolutionary descent, rather than overall similarities and differences.

Cladograms A cladogram links groups of organisms by showing how evolutionary lines, or lineages, branched off from common ancestors.

Building Cladograms A speciation event, in which an ancestral lineage branches into two new lineages, is the basis for each branch point, or node. Each node represents the last point at which the new lineages shared a common ancestor. A speciation event, in which an ancestral lineage branches into two new lineages, is the basis for each branch point, or node. Each node represents the last point at which the new lineages shared a common ancestor. The bottom, or “root,” of the tree represents the common ancestor shared by all organisms on the cladogram. The bottom, or “root,” of the tree represents the common ancestor shared by all organisms on the cladogram.

Building Cladograms A cladogram’s branching patterns indicate degrees of relatedness among organisms. A cladogram’s branching patterns indicate degrees of relatedness among organisms. Because lineages 3 and 4 share a common ancestor more recently with each other than they do with lineage 2, you know that lineages 3 and 4 are more closely related to each other than they are with lineage 2. Because lineages 3 and 4 share a common ancestor more recently with each other than they do with lineage 2, you know that lineages 3 and 4 are more closely related to each other than they are with lineage 2.

Building Cladograms This cladogram represents current hypotheses about evolutionary relationships among vertebrates. This cladogram represents current hypotheses about evolutionary relationships among vertebrates. Note that in terms of ancestry, amphibians are more closely related to mammals than they are to ray-finned fish! Note that in terms of ancestry, amphibians are more closely related to mammals than they are to ray-finned fish!

Reading Cladograms This cladogram shows a simplified phylogeny of the cat family. This cladogram shows a simplified phylogeny of the cat family.

Derived Characters A derived character is a trait that arose in the most recent common ancestor of a particular lineage and was passed along to its descendants. A derived character is a trait that arose in the most recent common ancestor of a particular lineage and was passed along to its descendants. The positions of the derived characters on the cladogram reflect the order in which those characteristics arose in a lineage. The positions of the derived characters on the cladogram reflect the order in which those characteristics arose in a lineage.

Reading Cladograms The trait of four limbs, for example, appeared before the trait of hair in the history of the cat’s lineage. The trait of four limbs, for example, appeared before the trait of hair in the history of the cat’s lineage.

Reading Cladograms Each derived character defines a clade. Hair, for example, is a defining character for the clade Mammalia. Each derived character defines a clade. Hair, for example, is a defining character for the clade Mammalia.

Reading Cladograms Retractable claws is a derived character shared only by members of the clade Felidae. Retractable claws is a derived character shared only by members of the clade Felidae.