Vertebrates

“Vertebrates are animals that possess a vertebral column and/or notochord at any point in their lives.”

Vertebrates

One of the ways life is classified is through the presence or absence of the vertebrate. Vertebrates and invertebrates evolved from a common ancestor that was speculated to have lived around 600 million years ago.

Evidence of true vertebrates began to appear 525 million years ago and ever since then, vertebrates have branched off into a long lineage that includes armoured fish and giant sauropods to woolly mammoths and modern man.

Characteristics of Vertebrates

A vertebrate is an animal that has all of the following characteristic features at some point in its life:

  • A stiff rod running through the length of the animal (it could either be the vertebral column and/or notochord)
  • Humans and all other vertebrates possess a notochord as an embryo and it eventually develops into the vertebral column.
  • A bundle of nerves run above the vertebral column (spinal cord) and the alimentary canal exists below it.
  • The mouth is present at the anterior portion of the animals or right below it.
  • The alimentary canal ends in the anus, which opens to the exterior. The tail extends after the anus.

Read More: Alimentary Canal

Classification of Vertebrates

Vertebrates are classified into 7 classes based on their anatomical and physiological features. They are:

Mammals (Class Mammalia)

This class of organisms have the ability to regulate their body temperature irrespective of the surrounding ambient temperature. Therefore, mammals are called endothermic animals and it includes humans and platypuses.

Main article: Mammalia

Birds (Class Aves)

From a biological perspective, birds are dinosaurs (more aptly called avian dinosaurs). This class of organisms are characterised by feathers, toothless beaks and a high metabolic rate. Furthermore, members of class Aves lay hard-shelled eggs.

Main article: Aves

Reptiles (Class Reptilia)

Reptiles include tetrapods such as snakes, crocodiles, tuataras and turtles. The characteristic feature of reptiles is that they are ectothermic in nature. Snakes are still considered tetrapods though they have no visible limbs. This is due to the fact that snakes evolved from ancestors that had limbs.

Main article: Reptilia

Amphibians (Class Amphibia)

Amphibians include ectothermic tetrapods such as frogs toads and salamanders. The distinguishing feature that separates amphibians from reptiles is their breeding behaviour. Most amphibians need a body of water to breed as their eggs are shell-less. Furthermore, they undergo metamorphosis where the young ones transform from fully-aquatic larval form (with gills and fins) to terrestrial adult form.

Main article: Amphibia

Bony fishes (Class Osteichthyes)

This class of fishes is characterized by their skeleton which is composed primarily of bone rather than cartilage (such as sharks). Class Osteichthyes is also the largest class of vertebrates today.

Cartilaginous fishes (Class Chondrichthyes)

As the name suggests, this class is characterized by the cartilaginous skeleton. Members include sharks, rays, skates and sawfish. Some sharks such as the massive Greenland shark can live for several centuries. A specimen that was tagged in 2016 was found to be at least 273 years old.

Also Read: Pisces

Jawless fishes (Class Agnatha)

These are very primitive fishes that have not changed much from fossil records for millions of years. They have a jawless, circular mouth with rows of small sharp which aid in holding and feeding on other fishes. Most members of this class are parasites and scavengers.

Main article: Cyclostomata

Important Questions on Vertebrates

  1. Which animals are vertebrates?

Animals that possess a backbone is classified as a vertebrate. There are a large number of vertebrates currently existing on earth and they are classified into 7 classes based on their physiological and anatomical features.

  1. What does it mean to be a vertebrate?

Vertebrates and invertebrates are speculated to have evolved from a common ancestor many million years ago. But today, from an evolutionary perspective, vertebrates are considered to be the most apex forms of life on earth. Their complex anatomy and physiology provide a significant advantage over invertebrates in the natural world.

  1. What are the 7 classes of vertebrates?

Vertebrates have been classified based on their anatomical and physiological characteristics into 7 groups. They are as follows:

  • Class Aves
  • Class Reptilia
  • Class Agnatha
  • Class Amphibia
  • Class Mammalia
  • Class Osteichthyes
  • Class Chondrichthyes
  1. Which vertebrates lay amniotic eggs?

Reptiles and birds primarily lay amniotic eggs. Mammals also lay amniotic eggs though they are specialized for internal development. However, prehistoric mammals laid eggs and some modern-day mammals still do.

  1. When did vertebrates appear?

The very first vertebrates are thought to have evolved 525 million years ago. The very first vertebrate is thought to have been Myllokunmingia. But other evidence points towards Pikaia gracilens as the very first vertebrate and the ancestor to all modern vertebrates.

Pikaia gracilens

An artistic interpretation of Pikaia gracilens based on fossil evidence

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