An alternative theory that had by then been long since discarded as irrelvant, base don observations taken when the Terrans were still active, is that the Mustang, PT Cruiser, Edsel, F-150 WERE the dominant life forms, since so much of the environment seemed to be adapted to their welll-being. Occasionally, these life forms could be seen disgorging some sort of parasitic bipedal lower life form. It was speculated that these parasites might well have caused the long slow decline of the dominant life form by acting like a systemic virus, much like a tapeworm. Evidently, the relationship had a symbiotic vector to it, as it appears from the fossilized remains of the quadrocycles, as they were called, that the bipedal parasites went extinct near the same time as the quadrocycles did.

Some scientists speculate that a cataclysm such as a giant meteor may have been responsible for the death of the quadrocycles; but this is speculative. No-one knows exactly why they went extinct, unless the parasites were responsible. It appeared there food sources, Cornerus Shellus and Cornerus Mobilus, may have dried up for unknown reasons. The largest of the quadrocycles, Quadrocyclus Petrotankus was not among the fossil remains found around the usual hunting grounds for the Cornerus species, but from the evidence found at several sites it appears that the dying Quadrocyclus haunted the old hunting grounds in large numbers, long after there was no food to be found there.

Speculations on Terran Life Forms and their History
Wrkkmllzy Pshawbrquiz, Chief Kroicklean of Thrummix
Wrrux, Brunnxel and Phiqqulrstuv, Galactico, 5323