Taxonomy (biology)

Taxonomy is a practice and science of classification, often with 2 parts: an underlying scheme of classes (a taxonomy)'s development and allocation of things to the classes (classification).

In biology, taxonomy is the scientific study to name, define, and classify groups of organisms based on characteristics, grouped as as taxa (s. taxon). Such groups are given a taxonomic rank; a higher ranked group is aggregated to form more inclusive guorp of higher rank thus making a taxonomic hierarchy. The principle rank in mdoern use are domain, kingdom, phylum. Swedish botanist Carl Lnnaeus is said to be the founder of the current taxonomy system, as he made the Linnaean taxonomy to categorize organisms.

Taxonomy (biology)

Phylogenetic Tree

Clades

In Traditional Classification

In Modern Classification

Dichotomous Keys

Phylogeny

Traditional Taxonomic

Linnaean System

Carl Linnaeus

The Nature of Classification

Great Chain of Being

References

Phylogenetic Tree

Phylogenetic Trees/Cladograms are the relationships, which are similar to family trees, but this instead tracks the entire species, rather than between members.

Cladistics is what guides the production of cladograms.

Clades

Species are grouped into clades, a taxonomic group with one ancestor species and all its descendants.

The tip of a branch is an entire species. Moving back on a branch on a phylogenetic tree is like moving back in time.

Each shaded area in the phylogenetic tree below highlights one clade, Which two clades are not shaded in?

In Traditional Classification

hierarchical classification system by Linnaeus

groups species primarily by observed morphological (physical) characteristics then arranges them into ranks
- pros: simple and convenient
- cons: no evidence of relatedness

Crocodiles are grouped with turtles, snakes and lizards based on their morphology

In Modern Classification

Organisms are grouped based on evolutionary relatedness /pathways (not limited to taxonomic ranks)
- pros: tells us about evolutionary relatedness
- cons: difficult to discover relatedness of fossils that date back millions of years

Crocodiles are grouped with birds because they share a more recent ancestor

Dichotomous Keys

Dichotomous keys are a series of branching used to identify organisms or objects.

Experts use this to identify organisms, which leads to the smallest classification units.

An animal with needle-like teeth and no ears belongs to the Order Insectivora, comprised of moles and shrews.

In each step, one must choose between two defining statements. Each alternative leads to a different choice. Eventually, it ends with the classification of the organism to a taxonomic level.

As illustrated below, a dichotomous key identifies an organism based on the presence or absence of care.

The dichotomous key above gives an easy way to identify five bird species.

But in reality, most of these diagrams used by experts are more complex to create and use.

To distinguish between thousands of bird species—herons have more than 60 types—the keys must use more detailed criteria. Before experts create the key, features must be agreed upon to tell apart all species, as well as learn the terminology for the names and describe the features.

A challenge for taxonomists is deciding what criteria to use for all taxons, with often disagreements occuring.

60,000 different species of parasitic wasps have been placed in a single family, the Ichneumoniadae. 9000 bird species are traditionally grouped into some 160 different families.

The names of some animals do not even indicate that they belong to that specific species, like the horseshoe crab, which are more related to spiders than true crabs.

Charles Darwin published in 1859, on the On the Origin of Species, where he depicted his theory of evolution, which states that all organisms are descended from a common ancestor in the same way family members are related to each other through a common ancestor, depending on the species.

Phylogeny

Phylogeny is the science of evolutionary relationships between an entire species.

Traditional Taxonomic

As the Linnaean System is the foundation of taxonomy, Traditional Taxonomy is the subsequent development of biological classification with similar features.

Linnaeus further grouped species into taxonomic levels/ranks based on shared appearances, each called a taxon (plural: taxa). His original system had five taxa and later added seven major levels: species, genus, family, order, class phylum, and kingdom.

taxon: a category used to classify

To improve the system, taxonomists have created many intermediate taxonomic levels, like subfamilies and superorders.

Although his grouping system was often criticized, his simple binomial naming system was a mjaor improvement. Species in the same genera could be expected to have similar appearances, thus the names of two species of the Ursus family, Ursus americanus (black bear) and Ursus maritimus (polar bear), must share many similarities.

Linnaean System

Carl's system, the Linnaean System is where most of the taxa used in taxonomy come from - the framework of the Taxonomy System.

It's still widely used today.

framework: base structure

Carl Linnaeus

Swedish naturalist Carl Linnaeus (1707 - 1778) is deemed the creator of taxonomy. He introduced a consistent way of grouping species according to their morphological/physical similarities, a system still use today. He believed species to be clear living types that can be grouped into categories called genera.

Linnaeus thought that species should have unique names and developed a binomial nomenclature system that's now the official system used to name species.

genera (singular genus): a taxonomic level of a group of similar species
binomial nomenclature: the formal system of naming species whereby each species is assigned a genus name with a specific name, forming the species' name

Salmon at different stages of their life look two different species.

Some members of the same species look very different due to being males or females, young or mature colouration.

Two birds are of the same species. Left: male, right: female

Scavenger

Carnivore

Producer

Herbivore

The Nature of Classification

Similarly to elements in Chemistry, organisms are classified in several ways. The grouping of organisms into categories of criteria is called biological classification.

biological classification: the grouping of organisms into biological categories based on physical and evolutionary relationships.

Organisms can be classified according to their role like:

The Taxonomy or the Science of Systematics, is the science of identifying and classifying all organisms on Earth, a very challenging science.

What makes this hard, is that those of the same species are variable, they change as they grow, and evolve.

As biologists use advanced technology in taxonomy, it helps them to look for the genetic data in their DNAs.

The first struggle was to create a scientific name per species. The common names for species aren't always helpful, like "robin", which is used for two different bird species.

Note: the name is italicized and only the genera is capitalized

In the Linnaean system, each taxonomic rank consists of species that have similar features.

E.g. all species in the phylum Chordata have a backbone and all members of the class Mammalia are warm-blooded.

The name of a phylum, class, order, and family or genus is capitalized, the name of the species is not capitalized.

Great Chain of Being

The Great Chain of Being or scala naturae is one of the many early grouping systems based on the philosophical assumption that each type of organism held a fixed rank on a scale from the lowest to highest, with humans at the top, mammals and birds above frogs and fish, and that everyone was above plants.

Many were hesitant to abandon this belief until Linnaeus was among the first biologists to doubt this system and believed that new species might arise by hybridization and that plants might change as they acclimatized to new environments.

acclimatized: adapt

In the first edition of his book Systema Naturae (1735), Linnaeus grouped species and genera into orders, classes, and kingdoms.

References

[1] Wikipedia
- [1.1] Taxonomic rank
- [1.2] Taxonomy (original)

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Taxonomy (biology)

Phylogenetic Tree

Clades

In Traditional Classification

In Modern Classification

Dichotomous Keys

Phylogeny

Traditional Taxonomic

Linnaean System

Carl Linnaeus

The Nature of Classification

Great Chain of Being

References

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