What makes a vertebrate
Animals that bear a backbone are called vertebrates.
They show a few characteristics in common at some stage of the life cycle — which is to say the grown animal may show none of them while the embryo does.
Figure to be added
| Shared characteristic | What it is |
|---|---|
| Notochord | A supporting rod running the length of the body; it later becomes the backbone. |
| Nerve cord | A hollow nerve tube lying above the notochord. |
| Gill slits | Slits in the neck region; in fishes they become the gills. |
| Post-anal tail | A tail extending beyond the anus. |
The five vertebrate classes
- Pisces
- Amphibia
- Reptilia
- Aves
- Mammalia
The order is not an accident
The five classes read as a route from water to land: fishes wholly in water, amphibians on both sides, reptiles on land, birds in the air. The number of heart chambers rises in the same order — from two to four.