As I explained before, common ancestry is considered linked to the concept of gradualism, and gradualism is intrinsically linked to natural selection via random mutations in regards to the development of life. It requires a substantial time of separation between major species that branch off to create wholly different species to construct a tree of life from a universal common ancestor that came from mainly one origin of life event:
“But many biologists claim they know for sure that random mutation (purposeless chance) is the source of inherited variation that generates new species of life and that life evolved in a single-common-trunk, dichotomously branching-phylogenetic-tree pattern!”
The Phylogenetic Tree Topples | American Scientist
I also made it clear that to say that the Adam and Eve story did not happen at all would be to directly challenge the divinity of Christ. Since the evidence identifies the designer to be Jesus and the common design model is consistent with the Genesis account, this is another reason why both models are mutually exclusive.
Lastly, in regards to your claim about the fossil record, a researcher examined the fossil record’s over/under representation of certain species or groups of organisms, and completeness for a species over the entire history of its existence. He ended up concluding that the fossil record is indeed complete, with about 10% of all species that have ever lived being represented (Baumiller 1999). Even though he suggested there are still some biases and stratigraphic gaps in the fossil record, these problems can be mathematically estimated from the available data.
Baumiller, T.K. 1999. Enough remains to work with. Science 283: 1271.
However, I was unable to find the study and read it myself. So I had to rely on secondary sources again, unfortunately.