Vertebrate Animals: Characteristics and Classification

Vertebrate animals belong to the Animal Kingdom and have the following characteristics:

• They have an internal skeleton that allows movement, protects the organs, and gives support to their body.
• They have blood to carry the nutrients and waste products throughout the body.
• They have articulated limbs (fins, wings, or legs).

We are going to study the vertebrates' groups:

1. Fish

• Aquatic (they have a fusiform body, thinner in the tips, and fins). They breathe through gills.
• Poikilothermic (they cannot maintain constant body temperature).
• They have a lateral line (a line that crosses their body that is able to detect vibrations in the water).
• They have external fertilization: gametes join in the environment, outside of the female's body.
• They can be oviparous (the embryo develops inside an egg outside the mother's body) or ovoviviparous (the embryo develops inside an egg inside the mother's body. Some sharks).
• There are two groups:

• Bony fish. Bony skeleton. Gills protected by an operculum. Examples: trout, salmon.
• Cartilaginous fish. Cartilaginous skeleton. Visible gills. Examples: sharks, rays.

2. Birds

• Terrestrial or aquatic, but all of them breathe through lungs.
• Homeothermic (they can maintain constant body temperature).
• Internal fertilization, oviparous.
• Body covered with feathers. Upper limbs are wings. The beaks' shape depends on the type of feeding. The shape of their legs depends on their habitat.
• Light body: they have air sacs between the organs and inside the bones.
• Two types:

• Flying birds. They can fly. Examples: eagles, parrots.
• Flightless birds. They cannot fly. Examples: ostrich, kiwi, penguins.

3. Mammals

• Terrestrial or aquatic, but all of them breathe through lungs.
• Homeothermic.
• Internal fertilization, oviparous or viviparous.
• Body covered with fur or hair. They are the only group of vertebrates that have ears (except for whales, dolphins, manatees, and seals).
• They have mammary glands that produce milk, from which the newborns feed.
• There are three groups:

• Monotremes. Oviparous. Examples: platypus, echidnas.
• Marsupials. Viviparous, but their babies finish their development inside an external pouch (marsupium). Examples: koala, kangaroo.
• Placentals. Viviparous with a placenta. Examples: tigers, elephants.