Because you're dealing with an ASSUMPTION made about the fossil record, both that the the fossil record is complete enough to make that determination accurately and that the conclusions about what allegedly evolved from what is correct, since no one was there to see it.
The evidence merely shows what was alive at one time and died and happened to be preserved. It can show what other creatures existed in the same vicinity and at the same time, especially if they were fossilized together, but beyond that, is speculation, not fact.
You can't say Scripture is wrong, when you don't even know what *right* is and a guess, aka hypothesis, is not a hard fact.
Genesis also makes no mention of primitive bacteria and slime molds, early life-forms which ARE in the fossil record and predate the first multi-cellular organisms (”sea creatures”) by hundreds of millions, if not billions, of years.