Do you have any idea what animals developed from the armored fish? You have seen the way in which the early fish had a spine made of cartilage, and the bone plates served to protect them. They probably needed to be armored because they could not swim particularly well. As they became more mobile, however, the need for the protective armor was reduced.
The bone cells slow began to move inwards, changing the cartilage into bone. Thus, the first fish with a true backbone evolved. It is interesting to note that modern sharks still have a spinal column which is made of cartilage because the ossification, as the change to the bone, is known, has not occurred in this group.
What animals developed from the armored fish?
The first bony fish appeared during early Devonian times, that is, about 380 million years ago. At the end of Devonian times, about 350 million years ago, the bony fish began to evolve very rapidly indeed and divided into two groups. The groups are the modern bony fish, which account for about 95 percent of all modern fish, and the remaining five percent is a group known as lungfish
The modern bony fish form a group in which there is just one single line of evolution. This evolution takes place as a gradual loss of the heavily armored scales together with changes in the structure of the jaw. The change in the jaw structure is mainly concerned with the way in which the mouth opens, but it is rather complicated and it is enough to say that modern fish are able to open their mouths far wider than their early ancestors.
This ability has obvious advantages when it comes to feeding. There are still lungfish living today. They differ from more familiar fish in two main respects. Firstly, they have internal nostrils rather than gills, and equally important, the structure of the fins is different.
In the true fish, the fins are formed on rays which extend from the body they are usually referred to as ray-finned. In the case of the lungfish, however, the fin rays enter an extension of the body tissue itself they are known as lobe-finned. This means that the fins of the lungfish eventually led to their ability to move on to land because of their development into legs.
Modern lungfish are able to survive for long periods when ponds dry out. They burrow into the mud at the bottom of ponds, only to emerge when the pond fills with water once again.
During Devonian times, the widespread desert climate tended to encourage the development of animals which were able to survive on land as well as in water. These animals were the amphibians. They first appeared in Greenland, which was furthest away from the return of the sea during carboniferous times some 300 to 350 million years ago.
You may like also:
- What is Evolution?
- What are a fossil and Which fossils are you most likely to find?
- What are the geologic column and the fossil record?
- What was the first life on Earth?
- Which are the most advanced animals without backbones?
- How have animals with backbones evolved?
- After the Amphibians – What next?
- Which Animals are among the Largest that have ever Lived?
- Which were the First Animals with Warm Blood?