Ecology and grouping organisms
The animal kingdom can be divided into two major phyla. Animals without backbones are invertebrates, such as spiders and insects. Animals with backbones are vertebrates. The vertebrates can be further divided into classes, such as mammals and birds.
|amphibians||moist permeable skin||frog, newt, salamander|
|fish||gills, wet scales||goldfish, shark, cod|
|reptiles||dry scales||crocodile, lizard, snake|
|birds||feathers,beaks||budgerigar, sparrow, ostrich|
|mammals||fur, produce, milk||rabbit, kangaroo, human, dolphin|
Some fossil vertebrates and newly discovered species can be difficult to classify. For example, Archaeopteryx is an extinct vertebrate known only by its fossil remains. It has characteristics of birds and reptiles.
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