Chondrostei facts for kids
Quick facts for kids Chondrostei |
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| Atlantic sturgeon, Acipenser oxyrinchus | |
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Chondrostei
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Acipenseriformes |
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The Chondrostei are a special group of ray-finned fish. They include amazing creatures like sturgeons and paddlefishes. Sturgeons are very large fish, famous for their caviar, which are their eggs. These fish are unique because their skeletons are mostly made of cartilage, not hard bone, especially when they are young.
There are 52 different kinds of Chondrostei. They are split into two main groups, called orders. One group is the Acipenseriformes, which includes sturgeons and paddlefishes. The other group is the Polypteriformes, which includes reedfishes and bichirs.
Chondrostei are mostly cartilaginous fish. This means their skeletons are soft and bendy, like the tip of your nose. They do have some ossification, which is the process of forming bone, but it's not as much as other bony fish.
Sometimes, people used to think Chondrostei were related to sharks. This is because they both have skeletons made mostly of cartilage. Also, their jaws are similar to sharks. Most Chondrostei, except for the Polypteriformes, do not have typical fish scales. They also have small breathing holes called spiracles. Sturgeons have a special tail shape called a heterocercal tail. This means the top part of their caudal fin is longer than the bottom part.
However, scientists have studied old fossils. These fossils show that Chondrostei are actually more closely related to other bony fish than to sharks. Their outer look can be a bit misleading!
How Chondrostei Evolved
Scientists believe that the ancestors of Chondrostei were once bony fish. But over a long time, they lost most of their bone. This made their bodies lighter. A lighter body helped them move faster and more easily in the water. Older Chondrostei do start to develop some bone in their skeletons. This suggests that bone growth is just delayed in these fish, not completely gone.
During the early Mesozoic Era, many fish were changing. They were developing ways to become lighter and faster. This helped them become better predators. Chondrostei took a very different path. They kept their skeletons mostly cartilage, which is lighter than bone. They also delayed bone growth until they were older. They even lost some bones in their upper jaw. These changes allowed them to quickly shoot their jaws forward to catch prey.
Why did Chondrostei change so much? There must have been strong reasons for them to adapt this way. One unique thing about them is that they have extra sets of chromosomes. Most animals have two sets of chromosomes, which is called diploid. But Chondrostei can have 8 or even 16 sets of chromosomes! This big genetic change might have allowed their bodies to reorganize quickly and drastically.
Understanding Fish Groups
The group "Chondrostei" is considered paraphyletic. This means the group does not include all of its descendants. It's like a family tree where some branches are missing from the main group. Because of this, scientists might reorganize how these fish are grouped in the future.
See also
In Spanish: Condrósteos para niños
