Recently, I was perusing a second hand bookshop near Ely and discovered the book Antares Dawn by Michael McCollum, published in 1989 (copyrighted 1986). It is an interesting book that uses wormhole-like "foldpoints" for passage between the stars and has ships that use spinning sections for on-board gravity.
Imagine my surprise when I came across an alien species called the Ryall that were described as green-grey-scaled semi-reptilian centauroids who upon encountering Humanity, started out with a genocidal assault that effectively wiped out several planets before they could be beaten back...
Now, I'm not saying that our wizardly celery-chaser stole the Ryall, filed the serial numbers off and put them up against a battle-moon, but I would not be surprised if RFC read the book when he was much younger and the Ryall took up residence in the deepest part of his subconscious, popping back up when he needed an evil alien race for Earth to unite against...
