: Why did some of my hatchling spiny softshells develop a curling in their posterior carapace, where the rear shell was almost cupped?
There is nothing to worry about. Some softies carapaces curl and some don't. I have a Texas Spiney with a curled carapace and a Malayan without. Doesn't seem to bother the Texas. As a matter of fact, it may flatten out as the turtle gets older. Hope this helps.