Vertebrate Animals: Fish, Amphibians, Reptiles, Birds, Mammals
Vertebrates
Vertebrates share these characteristics:
- Internal skeleton with a backbone.
- The body is usually divided into head, trunk, and tail.
- Four limbs.
- Bilateral symmetry.
- Complete digestive tube (mouth, anus) with digestive glands.
- Closed circulatory system.
- Nervous system.
- Sexual reproduction.
Fish
Habitat: Aquatic; can live in freshwater or marine environments.
Characteristics:
- Head, trunk, and tail.
- Limbs modified into fins.
- Scales.
- Swim bladder.
Vital Functions:
- Nutrition: Complete digestive system (mouth with teeth, stomach, intestine, anus). Diverse feeding habits. Breathe through gills.
- Interaction: Well-developed brain and sense organs. Lateral line is an exclusive sense organ (detects water vibrations). Poikilotherms.
- Reproduction: Most are oviparous with external fertilization.
Classification:
- Bony Fish: Skeleton made up of bone. Skin covered by scales. Have an air bladder to stabilize and float. Sexual reproduction with external fertilization (e.g., goldfish).
- Cartilaginous Fish: Skeleton is made up of cartilage. Skin covered by dermal denticles. Don’t have a swim bladder. Are mainly predators. Sexual reproduction with internal fertilization (e.g., shark).
Amphibians
Characteristics:
- Four limbs.
- Head, trunk, and tail.
- Skin is very thin and doesn’t have any protective structure.
- Have glands that produce mucus and keep the skin moist.
Vital Functions:
- Nutrition: Digestive system (mouth without teeth, stomach, intestine, anus). Young are usually herbivorous, adults carnivorous. Young breathe through gills, adults by lungs and skin.
- Interaction: Well-developed brain and sense organs. Most of them have poisonous glands. Poikilotherms.
- Reproduction: Fertilization can be internal or external. Oviparous, except salamanders are ovoviviparous. Young (tadpoles) have to change to become adults. They undergo metamorphosis.
Reptiles
Habitat: Terrestrial tetrapods. Most live in dry environments, although some spend a lot of time in water (e.g., crocodiles) and some are marine (e.g., marine tortoises).
Characteristics:
- Four limbs, except snakes.
- Head, trunk, and tail.
- Skin is thick and is covered by hard scales and doesn’t have glands; it protects them from water loss.
- Lizards and snakes shed their skin; tortoises have a hard shell carapace.
Vital Functions:
- Nutrition: Digestive system (mouth, intestine, stomach, anus). Most are carnivorous and have teeth to capture prey; turtles don’t have teeth but have a beak. Many snakes have poisonous glands connected to fangs. Breathe through lungs.
- Interaction: Well-developed brain and sense organs. Poikilotherms.
- Reproduction: Fertilization can be internal or external. Most are oviparous; some snakes are ovoviviparous.
Birds
Habitat: Terrestrial tetrapods; some are adapted to spend a lot of time in the water (e.g., penguins). Usually, they are flying animals, but some have lost that capacity (e.g., ostriches).
Characteristics:
- Have a fusiform, aerodynamic body that facilitates movement in the air.
- Body covered by feathers, legs by scales. Feathers are excellent insulation, protecting birds from water and cold.
- The upper legs are wings.
- Have some hollow bones to make the animal lighter and facilitate flight.
- Lungs have air sacs.
- Eyes and ears are highly developed; eyes are in a lateral position.
Vital Functions:
- Nutrition: Digestive system. Feeding habits are very varied; have a beak. The shape of the beak depends on what they eat. Breathe through lungs.
- Interaction: Well-developed brain and sense organs. Homeotherms.
- Reproduction: Internal fertilization. Oviparous.
Mammals
Habitat: Terrestrial tetrapods; some are aquatic (e.g., dolphins); only bats can fly.
Characteristics:
- Four limbs.
- Head, trunk, and tail.
- Head joined to the trunk by the neck.
- Skin is covered by hair, which protects against heat loss.
- Have glands, including mammary glands.
Vital Functions:
- Nutrition: Digestive system (mouth with teeth, lips). The shape of the teeth depends on what they eat. Breathe through lungs.
- Interaction: Well-developed brain and sense organs. Homeotherms.
- Reproduction: Internal fertilization. Viviparous. Young grow in the mother’s womb (uterus). Mammals are young, and females feed them with milk produced in their mammary glands.
Classification:
- Monotremes: Oviparous; have a beak without teeth (e.g., platypuses).
- Marsupials: Viviparous, but offspring are born very immature and have to complete their development inside the mother’s marsupium (e.g., kangaroos).
- Placentals: Young develop completely inside the mother’s uterus. The embryo is connected to the female by the placenta (e.g., monkeys).