Classification of Kingdom Animalia
Senior 2 · Biology
Classification of Kingdom Animalia
Lesson 3 of 5
20 min
Let's begin
On a morning drive through Akagera National Park you may see a Nile crocodile basking beside Lake Ihema, grey crowned cranes stepping through the wetland grass, and a pride of lions resting in the shade. These are a reptile, a bird and a mammal.
All three belong to vertebrate classes that fully conquered dry land. The key was an egg that does not dry out, and, in birds and mammals, a body that keeps itself warm.
Reptiles, birds and mammals are called amniotes. Their embryo grows inside a membrane called the amnion, which holds it in its own pool of fluid. In reptiles and birds this egg also has a shell, leathery in reptiles and hard in birds, so it can be laid on dry land. Fertilisation happens inside the female's body before the shell forms. This freed these animals from returning to water to breed, as amphibians must.
Question: A crocodile lies in the sun on the bank in the early morning, but by midday it has slid into the water. Explain this behaviour.
Solution: A crocodile is an ectotherm: it cannot make enough of its own body heat. In the cool morning it basks to absorb heat, so that its muscles and enzymes work well and it can move and hunt. At midday the sun would make it too hot, so it moves into cooler water. It controls its temperature by behaviour, not by its metabolism.
A beak's shape tells you what a bird eats. The African fish eagle over Lake Kivu has a hooked beak for tearing flesh. The shoebill in Akagera's swamps has a huge, broad beak for seizing fish. The grey crowned crane (umusambi) of the Rugezi and Akagera wetlands has a short, pointed beak for picking up seeds, insects and small animals.
Rwanda's mammals include the mountain gorillas of the Volcanoes National Park; the chimpanzees and L'Hoest's monkeys of Nyungwe; the lions, giraffes, zebras and hippos of Akagera; long-horned Inyambo cattle; and bats, the only mammals that truly fly.
| Class | Body covering | Temperature | Breathing | Eggs or young |
|---|---|---|---|---|
| Fish | wet scales | ectotherm | gills | eggs in water |
| Amphibians | moist skin | ectotherm | gills, then lungs and skin | jelly-coated eggs in water |
| Reptiles | dry scales | ectotherm | lungs | leathery eggs on land |
| Birds | feathers | endotherm | lungs with air sacs | hard-shelled eggs |
| Mammals | hair or fur | endotherm | lungs and diaphragm | mostly live young fed on milk |
Tip
Memory hook: feathers mean bird, and hair plus milk mean mammal. No other animals have them.
Watch out: scales alone do not identify a class. Fish, reptiles and even birds' legs have scales, and both birds and mammals have a four-chambered heart.
A bat flies, so a student calls it a bird. Give two features that show it is a mammal.
Solution: Any two: it has fur, not feathers; females feed their young on milk from mammary glands; it gives birth to live young; it has teeth, not a beak; it has external ears.
Explain two reasons why reptiles can live in dry places where amphibians cannot.
Solution: Reptiles have dry, scaly skin that cuts down water loss, while amphibian skin must stay moist. Reptiles also fertilise internally and lay shelled eggs on land, whereas amphibian eggs have no shell and must be laid in water.
Classify these animals as reptiles, birds or mammals: shoebill, python, chimpanzee, chameleon, hippopotamus.
Solution: Birds: shoebill. Reptiles: python, chameleon. Mammals: chimpanzee, hippopotamus.
A lizard and a rat of the same body mass are kept at 20 °C. Which needs more food each day? Explain.
Solution: The rat. It is an endotherm, so it must keep releasing energy by respiration to hold its body near 37 °C, well above the 20 °C air. The lizard is an ectotherm and lets its body cool to the air temperature, so it uses far less energy.
Summary
Sources and credits
The Rwandan examples, worked examples and practice questions are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
