Vertebrates Explained: Animals With Backbones
Vertebrates are animals with a backbone — fish, amphibians, reptiles, birds, and mammals. Definition, characteristics, classification, and how they differ from invertebrates.
Global Animal Guide · July 10, 2026
Quick answer
Vertebrates are animals with a vertebral column (backbone) made of bone or cartilage. They include fish, amphibians, reptiles, birds, and mammals — fewer than 5% of animal species, but most of the large animals people recognise. All vertebrates are chordates with a dorsal nerve cord; most have a closed circulatory system, paired sense organs, and organ-level body organisation.
Last updated: July 2026 — figures reflect widely cited zoological estimates.
What is a vertebrate?
The word comes from Latin vertebratus — “joint of the spine.” A vertebrate belongs to the subphylum Vertebrata (within phylum Chordata). Defining features include:
- A vertebral column (or, in a few lineages, a persistent notochord) protecting a hollow dorsal nerve cord
- A cranium (skull) housing a brain in most groups
- Organ-system body organisation
- Usually a closed circulatory system with a heart
Embryos of chordates share a notochord, pharyngeal slits, and a post-anal tail — vertebrates elaborate that plan into backboned animals.
The five living vertebrate groups
| Group | Skeleton / covering | Breathing | Examples |
|---|---|---|---|
| Fish | Bone or cartilage; scales common | Gills (most) | Shark, tuna, seahorse |
| Amphibians | Bone; moist skin | Lungs + skin | Frog, salamander, caecilian |
| Reptiles | Bone; scales / scutes | Lungs | Snake, crocodile, turtle |
| Birds | Bone; feathers | Lungs + air sacs | Eagle, penguin, hummingbird |
| Mammals | Bone; hair / fur | Lungs | Lion, whale, human, bat |
Birds evolved from theropod dinosaurs and are nested within reptiles in modern phylogeny — school textbooks still list them separately for clarity.
Vertebrates vs invertebrates
| Trait | Vertebrates | Invertebrates |
|---|---|---|
| Backbone | Present | Absent |
| Share of species | ~3–5% | ~95–97% |
| Circulatory system | Closed | Often open |
| Nervous system | Centralised brain + spinal cord | Variable (nets to ganglia) |
| Size extremes | Blue whale to tiny frogs | Giant squid to microscopic animals |
See our full guide: invertebrates explained.
Why vertebrates matter
Vertebrates dominate many food webs as apex predators, large herbivores, and pollinators (bats, some birds). They are also the focus of most conservation campaigns — partly because people relate to them, and partly because many are threatened by habitat loss, overfishing, and climate change.
Understanding vertebrate biology helps answer everyday questions: why sharks need to keep swimming, how frogs breathe through skin, why birds migrate, and how mammals regulate body heat.
Related reading
Frequently asked questions
What are vertebrates?
Vertebrates are animals with a backbone (vertebral column). Living groups are fish, amphibians, reptiles, birds, and mammals.
How many vertebrate species are there?
Roughly 70,000 described vertebrate species — a small fraction of all animals, most of which are invertebrates.
Are humans vertebrates?
Yes. Humans are mammals, and all mammals are vertebrates.
What is the largest vertebrate?
The blue whale — up to about 30 m (100 ft) long and over 150 tonnes.
Do all vertebrates have bones?
No. Sharks and rays have cartilaginous skeletons; hagfish retain a notochord without true vertebrae as adults.