Other ways of categorising vertebrates

Apart from skin covering, vertebrates can also be placed into one of the main sub-groups by looking closely at other features.

Three main features used for this purpose are:

1. Breathing system (whether the animal has lungs or gills, or can absorb oxygen through its skin)

Mnemonic depicting a breathing system in animals whether that be lungs or gills to absorb oxygen

With a vertical brace inserted, it might be difficult to breathe (breathing system).

Example

Image showing the differences of breathing systems in amphibians reptiles mammals and birds

Vertebrates that breathe using lungs will be classified as either mammals, birds, reptiles, or amphibians (adults).

Image showing mammals, amphibians, reptiles and birds use lungs to breathe

Vertebrates that breathe using gills will be classified as either amphibians (larva) or fish.

Image showing fish and amphibians_larva use gills to breathe

2. Thermoregulation – whether the animal can regulate its body temperature (warm-blooded) or changes temperature with the environment (cold-blooded).

Mnemonic showing thermoregulation in cold and warm blooded animals

A vertical brace would be cold, and a thermometer could show how much regulation was needed to maintain body temperature (thermoregulation).

Example

Vertebrates that are cold-blooded would fall into one of the following classes: fish, reptiles and amphibians.

Image of reptiles amphibians and fish as cold blooded categories of vertebrates

Vertebrates that are warm-blooded would fall into one of the following classes: birds or mammals.

Image of mammals and birds as warm blooded categories of vertebrates

3. Reproduction methods (internal or external fertilisation; live birth or lay eggs)

Mnemonic showing the reproductive methods of vertebrates either internal or external fertilization

Imagine a couple who have no children because their ability to reproduce is affected by their vertical braces restricting their movements (reproduction methods).

The reproductive methods of a vertebrate are a less accurate way of separating them into classes than using thermoregulation or breathing system, as there are exceptions within each class to the general rules. Because of this reproductive methods have to be used in conjunction with other methods in order to place a vertebrate into its appropriate class, and often can not be used as a dichotomous key.