Forerunner Halo effect

The Didact requested scans of the planet’s present biota along with lists of the flora and fauna that had survived the battles nine thousand years before. In the records of the survey conducted by the Lifeworkers, likely after the end of hostilities, I saw hundreds of species of larger animals ranging in size from a meter to a hundred meters—some clearly aquatic, others huge land carnivores or sedate prairie-grazers. This list was compared with what the sensors could now locate.
One by one, the larger species dropped out.
“No animals larger than a meter,” the ship’s ancilla reported in a precise, clipped voice.
Next came a range of historic species less than a meter in size—tree-hoppers, burrowers, small carnivores, seed-eaters, flying creatures, arthropods, clonal sibling societies … the Pheru.

One by one, they dropped off the current list. None to be found.
Next came flora, including dense arboreal forests. Many of the original trees had acquired a kind of long-term intelligence, communicating with each other over centuries using insects, viruses, bacteria, and fungi as carriers of genetic and hormonal signals, analogous to neurons.… That list also quickly emptied. There were remnants—dead forests and jungles covered with a false green carpet of primitive plants and symbiotic species.
All that remained, apparently, were mosses, fungi, algae, and their combined forms.
“Nothing with a central nervous system or even a notochord,” the ship’s ancilla reported. “No fauna above a millimeter in scale.”
(Halo:Cryptum; Ch.12)