Phylum chordates: subphylum vertebrates

Vertebrate animals are a very diverse subphylum of chordates, and are the animals that have backbones. It is a very diverse group that includes almost 62 extant species and many other fossilized ones.

Chordates are a group of animals characterized by having, at some point in their life or embryonic development, chorda or notochord, a skeletal axis that in the most evolved, vertebrates, gives rise to the vertebral column.

Within the chordate phylum , there are three major subphyla:

Urochordates or tunicates. They are marine, most of sessile life.
Cephalochordates, acraniums or amphioxus. Marine, they keep the notochord all their life.
Vertebrates. They replace the notochord with the spinal column during embryonic development.

Evolution of vertebrate animals

All vertebrates come from a common ancestor, so they have common characteristics. The first vertebrates to appear were the fish, from which the amphibians arose, which were still dependent on water but were able to live on dry land. Later, reptiles colonized almost all terrestrial environments, and later, birds and mammals appeared .

Ostracoderms

About 400 million years ago

Jawless fish with thick bony plates on their heads

Placoderms

About 380 million years ago

Jawed fish. They were armored fish, ancestors of sharks.

Amphibians

About 350 million years ago

Reptiles

About 300 million years ago

They managed to become independent of the water because their eggs are amniotic, with a hard shell that protects them from drying out and the amnion, which protects and feeds the embryo.

Mammals

240 million years ago

They arose from the therapsids, a group of reptiles .

Birds

225 million years ago

They arose from a group of reptiles.

Characteristics of vertebrate animals

The main characteristics of vertebrates are:

They have an internal bone or cartilaginous skeleton (rays, sharks,...) made up of:
- The skull, which protects the brain . Most of the sense organs are grouped in the head.
- The spine, its most characteristic feature.
- The limbs, which they use to move, such as fins, legs or wings. Tetrapods have four limbs.
They have a highly developed nervous system, made up of:
- Brain, protected by the skull.
- Spinal cord, protected by the vertebral column.
- Nerves.
Its symmetry is bilateral.
Your digestive system is made up of a tube with glands that are involved in digestion.
Your circulatory system is closed. The blood is pumped by the heart , which pushes it through blood vessels.
They capture oxygen through the respiratory system that has:
- Gills: The Aquatic Vertebrates.
- Lungs: The Terrestrial Vertebrates.
Your excretory system has kidneys with which they eliminate waste carried by the blood.
Their reproduction is sexual, with gonads (ovaries and testicles) producing gametes (ova and sperm).

Vertebrate Classification

Vertebrates are classified into the following groups:

Fish Superclass: Their bodies are covered in scales. They move by moving their fins. They are aquatic, both freshwater and saltwater. They breathe through gills. Included in this group are bony fishes and cartilaginous fishes.
Superclass Tetrapods: Has four legs or limbs.
- The amphibians. When they are born, they are tadpoles and, when they are adults, some can move to the terrestrial environment, although they always need to live near water. Their bodies are covered with moist skin. There are amphibians with tails but there are also others without tails.
- Reptiles are vertebrates that have adapted to the terrestrial environment, with their body covered with horny scales. Some reptiles have shells. Their legs are short, but some lack them.
- Birds are highly evolved animals that have managed to move by flight, although some swim, walk or run. Their bodies are covered in feathers. They have pulmonary respiration. They have two legs and two wings.
- Mammals are the most complex animals. They usually have the body covered with hair. The breasts of the females with which they produce milk to suckle their young are characteristic.