What Are Vertebrates?

One of the most interesting lessons I teach my high school students is on classification. It is fascinating seeing the students form an answer to the question "what is a fish?" or "what is a bird?" But before we can get down to what makes mammals, birds, reptiles, fish and amphibians different, we have to ask ourselves "what do they all have in common?"

Mammals, birds, reptiles, amphibians and fish are all members of the vertebrate phylum; but this begs the question:

"What are Vertebrates?"

Vertebrates are a group of animals that have backbones and spinal columns, that first appeared during the Cambrian Explosion around 525 million years ago. Vertebrates display the greatest difference in size of any group of organisms on Earth. Vertebrates range from frogs just a few millimetres long, to the mighty 33m blue whale! Despite the huge variety shown in this group, vertebrates comprise a mere 4% of all discovered animal species. This hub looks at the five major divisions of vertebrates, and what makes them unique.

The Vertebrate Groups

Pictures of Mammals

Mammals give birth to live young, have a covering of hair or fur, are warm-blooded, and feed their young using mammary glands.

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The Characteristics of Mammals

Mammals are possibly the most charasmatic of all of the vertebrates. Perhaps this is because we too are mammals, and feel a special affinity towards them. They are also (relatively) large, furry and cuddly - not many people call mammals creepy!. But what makes a mammal a mammal?

Mammals are named after mammary glands - a milk producing gland that all mammals use to feed their young. Additionally, mammals:

• Have a covering of hair or fur;
• Breathe air through lungs;
• Maintain a constant internal temperature (homeotherms)*;
• Undergo internal fertilisation and give birth to live young (are viviparous).

^{NB: Homeothermy is the correct scientific term for 'warm-blooded.'}

Pictures of Reptiles

Reptiles lay eggs with leathery shells, are covered in tough scales and are cold blodded

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The Characteristics of Reptiles

Dinosaurs were the greatest creatures to roam our planet, both in terms of size and many people's affection. Sadly, it doesn't seem this affection has been granted to the dinosaurs descendents! Reptiles (the group to which dinosaurs belonged) are often thought of as creepy, scary or even - quite incorrectly - slimy and disgusting. Reptiles are actually covered in dry scaly skin that prevents water loss - a problem that prevented the amphibians from severing all ties to the water.

In addition to their dry, scaly, waterproof skin, reptiles:

• Breathe air through lungs;
• Have a temperature that varies with the environment (poikilotherms)*;
• Undergo internal fertilisation;
• Lay leathery-shelled eggs (are oviparous) on land.

^{NB: Poikilothermy is the correct scientific term for 'cold-blooded.'}

Pictures of Birds

Birds have beaks and feathers, are warm-blooded, and lay hard shelled eggs.

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The Characteristics of Birds

Man has been fascinated by the flight of birds for thousands of years. In fact, the obsession with flapping flight probably set back the invention of the airplane by decades, if not centuries! Although not all birds can fly, all birds share the same set of adaptations:

All birds:

• Have a hard beak;
• Have feathers;
• Breathe air through lungs;
• Undergo internal fertilisation;
• Lay hard-shelled eggs (oviparous) in nests on land;
• Maintain a constant internal temperature (homeothermic).

Pictures of Fish

Fish absorb oxygen from the water through gills, are covered in scales and lay soft shelled eggs. They live in both marine and freshwater environments.

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The Characteristics of Fish

Fish spend their entire lives in water and are exquisitely adapted to this lifestyle.

Fish:

• Absorb oxygen from the water through gills;
• Have fins for swimming;
• Undergo external fertilisation;
• Lay soft shelled eggs (oviparous) in water;
• (Most) Have an internal temperature that varies with the environment (Poikilothermic).

There are several exceptions to these rules. Sharks, for example, give birth to live young and practice internal fertilisation. In fact, sharks lack a true backbone as their skeleton is made of cartilage and not bone.

Vertebrate Group Photos

• All species - videos, photos and facts - ARKive
  Most popular species. View videos and photos of 50 of the most popular species in nature. Learn more about their biology, threats and conservation.

Pictures of Amphibians

Amphibians have slimy skin and must return to water to breed. They lay soft shelled eggs and are cold-blooded

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The Characteristics of Amphibians

Amphibians were the first group of vertebrates to leave the water and walk on dry land. They even managed to grow to huge sizes before the dinosaurs took over the world. There are three types of extant amphibian - frogs and toads, salamanders and caecilians.

Many amphibians undergo a metamorphosis from a juvenile stage to an adult stage, with the adult stage adapted to life outside of water. One of the greatest differences between these stages is how the animal breathes. When juvenile, amphibians use gills to 'breathe' in water; when adult, amphibians lose their gills and develop lungs, although most can absorb some oxygen from water through their porous skin.

Amphibians:

• Breathe air through lungs (when adult);
• Have moist, porous skin;
• Undergo external fertilisation;
• Lay soft-shelled, gelatinous eggs in water;
• Have an internal temperature that varies with the environment (Poikilothermic).

Interviews with Animal Groups

Comments

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braden on March 15, 2018:

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jalylah on September 28, 2017:

so mammals really and only 9 on reptiles

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vibesites from United States on October 18, 2012:

Very interesting and absolutely educational, and recommended for students and little kids who are interested in biology. :)

Marcy Goodfleisch from Planet Earth on September 26, 2012:

Very nice hub, and so instructional for kids! I love the photos you included here!

Voted up!

Rhys Baker (author) from Peterborough, UK on September 19, 2012:

Yeah..I tried finding out some more and struggled. How I wish I had my uni papers access again.

I have a first class degree in Biology with a specialism in Toxicology and Cell Biology and a Teaching Certificate in Secondary Science.

I was arguing with my dept. head about the tongue map - she was adamant there were discrete regions until I showed her the changes. It actually makes sense. If you put something sour on the tip of your tongue, it tastes sour; if you put something sweet on the tip of your tongue it tastes sweet. I have no clue what unami is... :)

Lena Welch from USA on September 18, 2012:

I would agree with you on that one. I think the only reason I learned it was that my professor did a dissertation on birds. Finding the pages for you was hard. I had to look up monophyletic groups and birds and birds and cladistics.

A lot of education in the classroom is slow. A few weeks ago I learned that the taste bud maps were incorrect and they have known since 1974 - and it is still in classrooms!

What is your degree background?

Rhys Baker (author) from Peterborough, UK on September 18, 2012:

More to the point it shows how far education lags behind these discoveries - it seems the reclassification of reptilian occurred in 2004. This wasn't mentioned in my degree lectures, even as late as 2010!

It doesn't seem that this classification change is going to filter down below uni study as the change is so technical that birds and reptiles remain as two essentially separate groups only linked by a common ancestor that therefore requires both descendants to be recognised in the same Clade. It also seems to defy common sense for the traits that I previously listed. But you are right - it is fascinating...if highly technical!

Lena Welch from USA on September 18, 2012:

Aww the computer booted my edited comment with the easier to read article: http://www.ucmp.berkeley.edu/diapsids/avians.html

Lena Welch from USA on September 18, 2012:

Here is a great page explaining the phylogeny of animals. It shows the cladograms with birds as a type of reptile and explains why current thinking is placing birds with crocodiles.

http://biology.unm.edu/ccouncil/Biology_203/Summar...

Here is another one:

http://www.uwlax.edu/biology/Zoo-Lab/Lab-10/Reptil...

It is interesting to look at and really shows how much our views in science are still changing, even in areas that were once thought to be fairly absolute. Thus we get avian and non-avian reptiles.

Rhys Baker (author) from Peterborough, UK on September 18, 2012:

It would surprise me if birds were considered reptiles due to huge differences between them (birds are homeothermic, lay hard shelled eggs, have no teeth, possess a beak and are covered in feathers not scales) iamaware that research is revealing that they are much closer related to dinosaurs than we ever thought. But this doesn't make them reptiles. Scales, leathery eggs and polikilothermy would make them reptiles.

Nettlemere from Burnley, Lancashire, UK on September 18, 2012:

I can't vote for my favourite I like them all. Great hub though, ideal for biology classes and general interest.

Lena Welch from USA on September 17, 2012:

Interesting article as I just did this in Bio 175. Did you know that birds are now considered reptiles?