IKR!?That's weird. I've seen cannibalized mice in a trap but never just laying around like that.
No, chickens do not have access to that part of coop shed.Do you think the chickens got them?
Plus, they wouldn't have made such a precise excavation.
Pretty sure it must have been another mouse, more info and pics here:
https://www.backyardchickens.com/threads/what-would-eat-part-of-a-mouse.1524337/