Vertebrates

Think of an animal !

What animal did you pictured?

Did you know that when we say "animal", most people will think of a vertebrate?

I can be even more specific: most people will think of a mammal.

There are more than 57000 living species of vertebrates that inhabit nearly every part of the Earth.

But how do we define what is a vertebrate?

A vertebrate is an animal that possess a backbone or spinal column.

That includes mammals, birds, reptiles, amphibians and fishes.

The term vertebrate is derived from the vertebrae that are serially arranged to make up the spinal column, or backbone. The vertebrae form around the notochord during development and also encircle the nerve cord. The bony vertebral column replaces the original notochord after the embryonic period.

All vertebrates have the uniquely derived feature of a cranium, or skull, which is a bony, cartilaginous or fibrous structure surrounding the brain.

All vertebrates are built along the basic chordate body plan: a bilateral symmetry in their bodies, a stiff rod running through the length of the animal (vertebral column and/or notochord), with a hollow tube of nervous tissue (the spinal cord) above it and the gastrointestinal tract below.

Vertebrates are deuterostomes, whiwh means that the mouth is found at the anterior end of the animal, while the anus opens to the exterior before the end of the body. The remaining part of the body continuing after the anus forms a tail with vertebrae and spinal cord, but no gut.

There are aproximately 70.000 living species of vertebrates that inhabit nearly every part of the Earth. The diversity of living vertebrates is enormous, but the species now living are only a small proportion of the species of vertebrates that have existed.

Did you know that we estimate that for every species there are more than a 100 extinct species?

And their diversity is so extraordinary! Not only they vary in size (from 0,1 grams to 100.000 kilos ; from 7,7 millimeters to 33 meters), but in diet, reproduction and behavior!

The animals from the subphyllum Vertebrata are members of the phylum Chordata.

Vertebrates originated about 525 million years ago during the Cambrian explosion, which saw rise in organism diversity. The earliest know vertebrates had a fish-like apperance. The first jawed vertebrates, the "bony fishes", probably appeared in the late Ordovician and became common in the Devonian, also known as the "Age of Fishes". The Devonian also saw the appearence of the first Labyrinthodonts, a transitional form between fishes and amphibians. From there, Amniote animals evolved during the Carboniferous period: Birds evolved in the Jurassic while Mammals only managed to diverse and expand ath the end of the Triassic. The Cenozoic world whitnessed a huge diversification of bony fishes, amphibians, reptiles, birds and mammals.

All vertebrates share basic characteristics that are the product of their common ancestry, and the process of evolution can be analyzed by tracing the modifications of these characters. The processes and events of evolution are deeply related to the changes that occured on Earth during the history of vertebrates

There are two major groups of vertebrates: Amniotes and Non-Amniotes. They are distinguished on the basis of an innovation in embryonic development: the appearance of 3 membranes formed by tissues that come from the embryo itself. The membrane that interest us for this division is called Amnion, and animals that posess this membrane are called Amniotes (mainly terrestrial animals). These animals are divided into two main evolutionary lineages: the sauropsids (reptiles, birds) and the synapsids (mammals). Fishes and amphibians are Non-Amniotes animals.