UNIT 2

Animals and Adaptations

Animals are the group of living organisms characterized by both their ability to move and their requirement to consume other living things (such as plants or animals) for proper nutrition. Animals are commonly divided into two major groups: vertebrates (those with a backbone or spinal column) and invertebrates (those without). Over 50,000 species of vertebrates have been described and they make up the most common animals that we think of. These are often mammals, reptiles, amphibians, fish, and birds. However, more than 95% of described animal species are invertebrates. This includes various species of insects, squids, snails, worms, corals, and many more.

Adaptation occurs in response to changes in the environment, lifestyle, or relationship to other organisms. Adaptations can be physical, physiological, or behavioral. Adaptations are categorized into three major groups based on the habitats that cause them to occur – aquatic adaptations, terrestrial adaptations, and volant (flying) adaptations.

TOPIC 2A : Classifying Categories

Living things are classified based on unifying characteristics. Scientists start at broad levels of differences (vertebrates vs. invertebrates) and refine their classification for groups in greater detail as they become more specific.

Groupings are done based on like characteristics – students do not need to follow “official” classification structures – they just need to be able to recognize that you start with broad differences and become more specific in successive groupings. For example, you may look first at all animals with backbones, then group the animals with scales by looking at both fish and reptiles, and group them again by animals with fins and animals without. This leaves you with the fish group, categorized as an animal with a backbone, scales, and fins.

The five most common classes of animals belong to the vertebrates. They are mammals, birds, reptiles, amphibians, and fish. They are categorized by the following common features:

  • Mammals – Fur or hair, warm-blooded, live birth
  • Birds – Feathers, warm-blooded, hard-shelled eggs, most fly
  • Reptiles – Scales, cold-blooded, leathery-shelled eggs
  • Amphibians – Slimy skin, cold-blooded, jelly eggs, metamorphosis
  • Fish – Slimy scales, cold-blooded, jelly eggs, fins, gills

It is important to keep in mind that there are always exceptions to a rule, which is why these are very general descriptions of these classes of animals. For example, the platypus is an egg-laying mammal, penguins and ostriches are birds that do not fly, and some sharks, which are fish, have live birth.

Invertebrates are also grouped into classes, though because there are so many of them, there are also a lot of classes. Some common ones to remember are:

  • Arthropods – Exoskeleton, jointed legs, and a segmented body. Grouped further into Insects, Arachnids, Crustaceans, and Centipedes/Millipedes.
  • Cnidaria (neye-dare-ia) – Members include jellyfish, corals, anemones.
  • Mollusks – Members include snails/slugs, clams/mussels, squid/octopus
  • Annelids – Worm species including earthworms

TOPIC 2B: Amazing Adaptations

An adaptation is an internal or external feature or behavior that allows an organism to survive in its habitat. Some animals, such as birds, can have both physical and behavioral adaptations, i.e. having wings allows them to fly and many birds migrate due to seasonal changes in their environment. Birds also have specialized beaks and feet that allow them to survive in their habitats. A pelican has webbed feet for swimming and a beak with a pouch so it can car-ry its food and move to a safer place to eat it. Other birds like raptors can car-ry their food in their sharp talons, and have a large hooked beak to shred their food into smaller pieces for easier digestion. Most animals have a combination of adaptations that help them survive in their habitats.

Adaptations are also a way to classify animals. Adaptations are grouped according to the habitats that cause them to occur – aquatic adaptations, terrestrial adaptations, and volant (flying) adaptations. These adaptation categories could be subcategorized further. Consider terrestrial adaptations, for example, which can be grouped more specifically into desert adaptations, arboreal (tree) adaptations, arctic adaptations, subterranean (underground) adaptations, and so on. Just like classifying animals based on their characteristics alone, classifying adaptations based on the habitat is a way to show similarities and differences between animals that look different but still need to survive in the same way.