As this site notes, for a tiny, light-boned forest animal to have a spotty record of preservation is no shock.
If you are willing to admit the possibility that an Intelligent Designer directly-created the First Living Cell... then why not all of them?
Because of all the evidence for common descent. And, no "common design" does not cover all of it equally well. I call your attention especially to the sections on redundant pseudogenes and endogenous retroviruses under Part 4. Of course, reading and absorbing that might interfere with the 20-second response latency preferred by Holy Warriors on these threads.
What if the Designer is using a genetic algorithm and a great deal of time? :))
Your 'evidence' for common descent is startlingly similar to the 'evidence' for the hazards of second hand smoke; it consists entirely of opinion, and 'study' to gloss over the thousands of chasms that cannot be bridged by anything but assumption, such as Punctuated Equilibrium.