Bird skeletons are very delicate, and therefore, difficult to be preserved. The bones of the birds are soft. The small animals are very prone to physicochemical as well as biological decay. This is why the fossil record of bird is incomplete and well-preserved fossils of birds are rare to find, except at a few unusual sites.
The answer to your question is bacteria
Answer:
2)They have similarities in their embryonic stages that don’t exist in their adult forms
4)They all contain a backbone, or spinal column
Explanation:
In the embryonic development of vertebrates during the early stages of development there are great similarities. Vertebrates in the early stages as shown in the image are very similar and subsequently develop the structures of their own species that differentiate them.
The presence of notocorde is a characteristic characteristic of vertebrates and birds, fish, reptile amphibians and mammals have it since they are embryos to adults
Solidified, solidifying. 1. to make solid; make into a hard or compact mass; change from a liquid or gaseous to a solid form. 2. to unite firmly or consolidate.
