it is odd... i guess it would have to be some sort of sickness or virus... If there were no signs leading up to it to give you an idea what it was, its hard to say if your other birds are at risk or not... Do you have a vet or anywhere near you that will test your chick for cause of death? I...
huh... I assume the flat look is just from the other chick with it walking on it or pecking it once it was dead...
were there any signs of sickness or weakness at all in days or more prior?
What are the temps in the coop? Does it fluctuate a lot from daytime to nighttime?