Taxonomy

Classification is the arrangement of organisms into similar or related groups. We classify living things based on evolutionary relationships and similarities in their biological structures, beginning with the most general. Once an organism is classified, it can be given a scientific name. Taxonomyis the science of identifying, classifying and naming living things. The classification tree in the video looks like there are only a few phyla. In reality, each kingdom branches into many phyla—we just didn’t have room to show all of them! The kingdom of Animalia alone contains over 30 phyla. These include Echinodermata, which means “spiny skin” and contains organisms like sea urchins and starfish; Annelida with long, segmented bodies like earthworms; and Chordata with spinal cords, like humans. Each phylum branches into many classes and each class into many orders, and so on down to species. There are 1,470,000 species in the animal kingdom in total.

• There is always an equal number of kingdoms as phyla.
• A single phylum branches out into over 30 kingdoms.
• Each of the six kingdoms has exactly 30 phyla in it.
• Many different phyla make up each kingdom.

Classification is done by asking a series of yes or no questions. This questioning method is called a dichotomous key. Each question is about physical structures and is based on whatever it is that divides members of that kingdom, phylum, class, order, family or genus. Questions might include: Does it bear its young live or lay an egg? Does it have gills or lungs? Does it have hair, fur, scales or feathers? The dichotomous key helps us to classify organisms in an organized manner."Dear King Phillip Come Over For Good Soup" is a mnemonic device that can help you remember the order and names of the different levels of classification. The first letter of each word is the same as the first letter for the different levels of classification—Domain, Kingdom, Phylum, Class, Order, Family, Species.
The dichotomous key

• helps classify organisms through yes or no questions.
  
• unlocks the names of different organisms in a family.
  
• groups animals that lay eggs with animals that have live births.
  
• asks multiple questions about how organisms behave and act.
  

Just like people have first and last names, each living organism is given a scientific name with two parts. The first part identifies the genus and the second identifies the species. Unlike people's names, scientific names do not tell the family in which the organism belongs. However, any two organisms from the same genus already belong to the same scientific family.The genus name starts with a capital letter, the species name with a lowercase letter. The genus is a grouping for several related species. Some well-known examples of these names might be Tyrannosaurus rex or the common house cat, Felis domesticus. Scientists use these names to be sure that there's no question about what each creature is and how different organisms are related. So before naming an organism, it must first be classified into a kingdom, phylum, class, order, family, and finally, genus and species.For an organism’s scientific names, the first part is the ________ and the second is the ________.

• species, genus
  
• kingdom, phylum
  
• genus, species
  
• class, order
  

Paleoanthropology is the study of ancient humans. Typically, paleoanthropologists only find little pieces of fossils from ancient humans, so they don’t have a whole lot to work with. But in 1974, 40% of the skeleton of an ancient human was discovered in Ethiopia. This was a huge breakthrough. Called “Lucy,” the skeleton was Australopithecus afarensis, which is an extinct hominid that lived between 3.9 and 2.9 million years ago. This genus eventually evolved into the genus we now know as Homo. Lucy had a small brain, but she walked upright. This proved to scientists that pre-human species walked on two feet before their brain size increased.Which of the following is the best evidence to support the theory that Lucy’s genus, australopithecus, evolved into the genus homo?

• Lucy lived millions of years ago.
• Pre-human species had brains
  
• 40% of Lucy’s skeleton survived.
  
• Lucy walked upright on two feet.
  

Let's classify one common animal: the house cat. A cat is in the kingdom of Animalia because it is a complex, multicellular organism. It has a nervous system, so it’s in the phylum Chordata. Since it nurses its young and has a backbone, its class is Mammalia, or mammals. This is the same class as humans and is different from other creatures with backbones like birds, amphibians or reptiles. With teeth that are specialized for eating meat, it is in the order Carnivora, or carnivores (as opposed to plant-eating herbivores). Unlike other carnivores like dogs or whales, a cat has special claws that it can retract and whiskers that it uses to sense its surroundings. That puts it in the family Felidae, which includes all kinds of cats or felines. Because it can't roar, but can purr, it is in the genus of Felis. That means that while it isn't one of the great cats, like a lion, tiger or jaguar, it is a kind of feline. Finally, its size, hair and temperament place it into the species domesticus, which means domesticated (living among humans). The scientific name for the common house cat is Felis domesticus.Which of the following does the house cat have in common with a human?

• order and species
  
• kingdom, phylum and class
  
• order, family and genus
  
• kingdom, phylum, class and order