Classification of Living Things

As we look at all of the living things on earth and consider the fossil evidence of every living thing that has come before, we can start to group species by their similarities. Taxonomy is the process of classifying species. The following are the terms we use to make progressively smaller groups:

Domain - All living things fit into one of three categories: Eukarya, Eubacteria, Archaebacteria
Kingdom - similar to domains, but eukaryotes are divided up: Archaebacteria, Eubacteria, Protists, Plant, Animal, Fungi
Phylum - each kingdom has smaller divisions called phyla. Ex: Chordata - animals with spinal cords
Class - smaller divisions of phyla. Ex: Mammals are a class in the phylum chordata.
Order - smaller divisions of classes Ex: Primates are an order of mammals.
Family - smaller divisions of orders Ex: Hominids are a family of primates.
Genus - the smallest "group" name Ex: Homo
Species - a group that is capable of having fertile offspring Ex. sapiens

Each taxonomic level has certain things in common. It often helps to understand how some of these groups are defined.

Kingdoms

There is some technical stuff that separates the two prokaryotic kingdoms, but generally all living things fit into one of these groups:

Archaea - really old prokaryotes, sometimes chemosynthetic

Eubacteria - most of the prokaryotic bacteria you've ever heard of

Protists - single celled eukaryotes - with some exceptions like kelp

Algae - plant-like protists
Protozoa - animal-like protist
Fungus-like protists - fungus-like protists

Plants - multicellular autotrophs with cell walls

Fungi - multicellular heterotrophs with cell walls

Animals - multicellular heterotrophs without cell walls

Phyla

A phylum is a division of a kingdom. There are roughly 35 animal phyla, but here are a few as samples:

Porifera: Sponges - no true tissues

Cnidaria: Jellyfish - true tissues, no central nervous system, digestive system has only one opening

Arthropoda: Insects, Spiders, Crustaceans - have exoskeleton and jointed legs

Mollusca - snails, seashells, octopi - most have shells and a "muscular foot"

Chordata - fish, reptiles, mammals - have a spinal cord that runs along their back

Classes of Chordates

The phylum Chordata technically includes lancets and tunicates, but for the most part it is the group of vertebrates - animals with skeletons on the inside.

Fish - Have a 2 chambered heart, exothermic (cold blooded) and breathe through gills

Amphibians - have a 3 chambered heart, exothermic, breathe through gills as larvae, but develop lungs as adults

Reptiles - have a 3 chambered heart, exothermic, amniotic eggs (have layers for food, gas exchange and protection) and scales

Birds - have a 4 chambered heart, endothermic (warm blooded), feathers

Mammals - 4 chambered heart, endothermic, some kind of body hair, females have mammary glands that produce milk.