Question

2.Which group of animals were the first on land? a. How were the young of this group still like fish? b. How were the adults of this group different from fish?

Answer 1

• The first animals on land were Ichthyostega, they moved like seals. They lived 374 – 359 million years ago and it was a transitional species between fish and terrestrial animals.
• Similarities with young of this group and fish

1. Ichthyostega was long like the fishes.
2. They had a small dorsal fin along the margin of its tail, the tail was composed of a series of bony supports that are similar to the tail supports found in fishes.
3. They had a short snout region and a preopercular bone in the cheek region which is similar to the gill cover found in fishes.
4. They had small scales on the body like the fishes.

• Difference between the adult of this group and fish

1. These are transitional species between fish and land animals. They had a series of robust bones that supported the limbs, this character is similar to tetrapods but these are different from fish.
2. They had strong ribs and they were terrestrial on the other hand fishes are aquatic.
3. Their skull and limbs are similar to tetrapods and these features are absent in fishes.