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The animal kingdom is divided into invertebrates and vertebrates. Vertebrates are animals with backbone or vertebrae. They represent the majority of the phylum Chordata.

They are found in land, oceans, rivers, forests, mountains and deserts.

This course covers the following:

  • Characteristics of vertebrates and classify them.
  • Characteristics, classification, and life cycles of
  • Parental care in amphibians.
  • Flight adaptation and patterns of bird migration.

Vertebrates first appeared during the Cambrian, more than 500 million years ago. These early vertebrates lacked jaws and hence were called Agnatha.

Jawed vertebrates, called Gnathostomata, did not appear for another 100 million years. Gnathostomata are classified as pisces, amphibians, reptiles, aves, and mammals. 

All vertebrates are eukaryotic, multicellular, heterotrophic, and bilaterally symmetrical. They have two pairs of jointed locomotor appendages, which include fins and limbs.

In these animals, skeletal, muscular and nervous system are well-developed and metamerically segmented.

Characteristics of Vertebrates

  • Vertebrates are characterized by the following:
  • Highly-developed, skull-enclosed brain
  • Ventral heart with 2-4 chambers and closed circulatory system
  • Digestive system with well developed coelom,  large digestive glands, and organs like liver, and pancreas
  • Replacement of notocord (found in invetebrates) by vertebral column. Nerve cord enclosed by vertebrae. Bony or cartilaginous endoskeleton consisting of cranium, visceral arches, limb girdles, and 2 pairs of appendages.
  • Presence of well developed sense organs
  • Most vertebrates have separate sexes, each with paired gonads (except birds have only one ovary in left)

Vertebrates are classified into two different super classes, which are further classified into different classes shown in Figure 1:

Classification of Vertebrates
Figure: 1 Classification of Vertebrates

Agnatha (lamprey, hagfish) are jawless fish (Figure 2) that contain have a cyclostomic (circular) toothed mouth with which they bore into the side of a fish and suck the blood of their prey.

An Alaskan lamprey (Agnatha)
Figure 2: An Alaskan lamprey (Agnatha)

 Pisces ( salmon, trout) are cold blooded vertebrate animals that live in fresh and salt water and use gills to obtain oxygen and are distributed all over the world (Figure 3).

Arowana in an aquarium
Figure 3: Arowana (Pisces) in an aquarium

Amphibians (frog, toads) are cold blooded animals (Figure 4) that can live in both land as well as water.

Frog, an amphibian
Figure 4: Frog (Rana esculenta), an amphibian

Reptiles (snakes, lizards, salamanders) are air-breathing vertebrates with body covered with scales, bony plates, or a combination of both.

King Snake (Vertebrate)
Figure 5: King Snake (Lampropeltis getula californiae)

Aves (humming bird, peacock,  ostrich ) commonly known as birds are feathered (Figure 6), winged, bipedal, warm-blooded, egg-laying, vertebrate animals.

Peacock (Vertebrate), a large colorful pheasant known for its beautiful feathers
Figure 6: Peacock (Pavo cristatus), a large colorful pheasant known for its beautiful feathers

Mammals (monkeys, sloth, monotremes, humans) are warm blooded vertebrates characterized by the presence of mammary glands and body covered with hair.

Two-toed Sloth (Vertebrate), an arboreal mammal
Figure 7: Two-toed Sloth (Choloepus didactylus), an arboreal mammal