Consider that sea levels have changed considerably over the past ~5 million years, over which the Aquatic Ape (Hardy/Morgan) hypothesis might have occurred, and might be anywhere from 100 metres blelow current levels (putting fossils underwater at present) to 300 metres above.

Plus all the other usual challenges to fossil preservation.

That record is quite probably far more partial than appreciated.

<https://en.wikipedia.org/wiki/Aquatic_ape_hypothesis>

<https://en.wikipedia.org/wiki/Past_sea_level>

That said, I've no particular argument for or against the Aquatic Ape theory.